Transport- og Boligudvalget 2018-19 (2. samling)
TRU Alm.del Bilag 45
Offentligt
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Limfjord tunnel
Assessment and retrofitting
Technical Summary Report, Version 1.0
Date
25. juni 2019
 TRU, Alm.del - 2018-19 (2. samling) - Bilag 45: Orientering om rapport om vedligeholdelsesstrategi for Limfjordstunnelen, fra transportministeren
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List of contents
1
 
2
 
Executive Summary .................................................................................................................. 6
 
Background and objectives ................................................................................................... 10
 
 
Introduction ...................................................................................................................... 10
 
 
Methodology .................................................................................................................... 12
 
References............................................................................................................................... 14
 
 
Normative references ...................................................................................................... 14
 
 
Background documents ................................................................................................... 14
 
Description of tunnel .............................................................................................................. 16
 
 
Structural layout ............................................................................................................... 16
 
 
Soil conditions .................................................................................................................. 18
 
 
Construction method ........................................................................................................ 19
 
4.3.1
 
Earth works ................................................................................................................... 19
 
4.3.2
 
Concrete works ............................................................................................................. 21
 
4.3.3
 
Installation of elements ................................................................................................. 22
 
4.3.4
 
Joints............................................................................................................................. 24
 
4.3.5
 
Waterproofing membrane ............................................................................................. 25
 
 
Early defects .................................................................................................................... 26
 
4.4.1
 
Leakage ........................................................................................................................ 26
 
4.4.2
 
Settlement and deformation monitoring ........................................................................ 27
 
 
Repair and strengthening works ...................................................................................... 27
 
4.5.1
 
Background ................................................................................................................... 27
 
4.5.2
 
Activities (1990 – 2018) ................................................................................................ 28
 
4.5.3
 
Current activities ........................................................................................................... 30
 
 
Crack injection campaigns ......................................................................................... 30
 
 
Other activities ........................................................................................................... 31
 
 
Recorded settlements ...................................................................................................... 31
 
Geotechnical assessment ...................................................................................................... 32
 
 
Summary of results, geotechnical expert group .............................................................. 32
 
 
Input to structural assessment ......................................................................................... 34
 
Condition assessment ........................................................................................................... 35
 
 
Introduction ...................................................................................................................... 35
 
 
Compressive strength ...................................................................................................... 36
 
 
Top slab ........................................................................................................................... 37
 
6.3.1
 
Outer part ...................................................................................................................... 37
 
6.3.2
 
Inner part....................................................................................................................... 38
 
 
Interface/cohesion assessment ................................................................................. 39
 
 
Chloride content ......................................................................................................... 39
 
3
 
4
 
5
 
6
 
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7
 
 
Water content............................................................................................................. 40
 
 
Corrosion (current level/risk of future corrosion) ....................................................... 40
 
6.3.3
 
Fire protection ............................................................................................................... 41
 
 
Outer walls ....................................................................................................................... 42
 
6.4.1
 
HCP measurements and break outs ............................................................................ 42
 
6.4.2
 
Chloride content ............................................................................................................ 42
 
6.4.3
 
Water content................................................................................................................ 42
 
 
Mid wall ............................................................................................................................ 43
 
6.5.1
 
HCP measurements and break outs ............................................................................ 43
 
6.5.2
 
General condition .......................................................................................................... 43
 
 
Bottom slab ...................................................................................................................... 43
 
6.6.1
 
Post tensioning cables .................................................................................................. 43
 
6.6.2
 
Chloride content ............................................................................................................ 44
 
 
Immersion joints and closure joint ................................................................................... 44
 
 
Conclusions ..................................................................................................................... 46
 
Structural assessment ........................................................................................................... 48
 
 
Introduction ...................................................................................................................... 48
 
 
Purpose............................................................................................................................ 48
 
 
Safety, loads combinations, loads and material strengths .............................................. 48
 
7.3.1
 
Accidental actions ......................................................................................................... 49
 
 
Fire ............................................................................................................................. 49
 
 
Ship impact scenarios................................................................................................ 49
 
 
Flooded tunnel ........................................................................................................... 50
 
 
Longitudinal analyses ...................................................................................................... 50
 
7.4.1
 
Introduction ................................................................................................................... 50
 
7.4.2
 
Structural system .......................................................................................................... 50
 
7.4.3
 
FE-models..................................................................................................................... 50
 
 
Geometry ................................................................................................................... 51
 
 
Sectional properties ................................................................................................... 51
 
 
Support conditions ..................................................................................................... 51
 
 
Loads ......................................................................................................................... 51
 
7.4.4
 
Results, sectional forces and stresses ......................................................................... 52
 
 
Model 1, 2-D shell model ........................................................................................... 52
 
 
Model 2, 3-D model ................................................................................................... 54
 
 
Model 3, 2-D beam model ......................................................................................... 54
 
7.4.5
 
Sensitivity analyses ...................................................................................................... 54
 
7.4.6
 
Capacity verifications .................................................................................................... 54
 
 
Bending moment capacity ......................................................................................... 55
 
 
Shear capacity, global shear ..................................................................................... 56
 
 
Shear in construction joints........................................................................................ 56
 
 
Bearings ..................................................................................................................... 57
 
 
Piles ........................................................................................................................... 58
 
7.4.7
 
Flooded tunnel .............................................................................................................. 58
 
7.4.8
 
Summary of utilization ratios, longitudinal direction...................................................... 58
 
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8
 
9
 
10
 
 
Transverse analyses ........................................................................................................ 59
 
7.5.1
 
Introduction ................................................................................................................... 59
 
7.5.2
 
Analyses of transverse Properties ................................................................................ 59
 
 
Geometry and sectional properties ............................................................................ 60
 
 
Support conditions ..................................................................................................... 60
 
 
Results ....................................................................................................................... 61
 
7.5.3
 
Capacity verification ...................................................................................................... 62
 
 
Properties................................................................................................................... 62
 
 
Results ....................................................................................................................... 62
 
7.5.4
 
Non-linear analyses by FEM software .......................................................................... 63
 
 
Assumptions .............................................................................................................. 64
 
 
Results ....................................................................................................................... 64
 
7.5.5
 
Assessment of interface between original and repair concrete of the roof .................. 66
 
 
Shear capacity according to section 6.2.5 in DS/EN 1992-1-1 including DK NA ...... 66
 
 
Shear capacity according to section 6.3.4 in FIB Model Code 2010 ......................... 68
 
 
Interface/cohesion assessment ................................................................................. 68
 
 
Condition assessment ............................................................................................... 68
 
 
Conclusions ..................................................................................................................... 69
 
7.6.1
 
Longitudinal direction .................................................................................................... 69
 
7.6.2
 
Transverse direction ..................................................................................................... 69
 
Basic Maintenance and Repair Strategy ............................................................................. 70
 
 
Introduction ...................................................................................................................... 70
 
 
Actions recommended ..................................................................................................... 70
 
 
Inspection and monitoring................................................................................................ 71
 
 
Preventive maintenance and repair ................................................................................. 73
 
 
Trigger values .................................................................................................................. 73
 
8.5.1
 
Total settlements .......................................................................................................... 73
 
8.5.2
 
Differential settlements ................................................................................................. 74
 
8.5.3
 
Condition monitoring ..................................................................................................... 75
 
8.5.4
 
Key parameters and trigger values - Overview ............................................................ 75
 
 
Expected repair activities until 2069 ................................................................................ 77
 
 
Conclusions ..................................................................................................................... 78
 
Retrofitting strategies ............................................................................................................ 79
 
 
Methodology .................................................................................................................... 79
 
 
Geotechnical strategies ................................................................................................... 79
 
9.2.1
 
Purpose......................................................................................................................... 79
 
9.2.2
 
Optioneering process.................................................................................................... 79
 
9.2.3
 
Preferred Geotechnical Option: Active horizontal compensation grouting ................... 80
 
 
Structural strategies ......................................................................................................... 83
 
9.3.1
 
Purpose......................................................................................................................... 83
 
9.3.2
 
Additional prestressing ................................................................................................. 83
 
9.3.3
 
Replace bearing blocks ................................................................................................ 86
 
Costs ........................................................................................................................................ 88
 
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Introduction .................................................................................................................... 88
 
 
Retrofitting Budgets ....................................................................................................... 90
 
 
50 years budget ............................................................................................................. 90
 
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1 Executive Summary
Objective
The objective of the work carried out by the Structural Expert Group and summarized in this report has
been to provide the Danish Road Directorate with suitable and practical guidance to maintain, repair
and correct (where relevant) the structures of the Limfjord Tunnel for the remaining lifetime of the tun-
nel until the year 2069.
Background
The Limfjord Tunnel was completed in 1969 and it was soon realised that the water-proofing mem-
brane of the tunnel was not functioning properly, as seawater was observed to be leaking through
cracks in the tunnel roof and outer walls.
During the first 25 years of service, recorded settlements of the tunnel up to approximately 95 mm
have significantly exceeded the originally predicted design settlements of 30 mm. During the same ini-
tial 25 year period the length of the tunnel has increased by up to 1 mm per year, this is due to the
seasonal temperature variation experienced in the tunnel (resulting in cracks remaining permanently
open).
Continued leaking of water into the tunnel in combination with the internal walls being exposed to de-
icing salts has resulted in corrosion of the reinforcement at the internal face of the walls and roof slab.
Post-tensioning cables were installed below the pavement in the tunnel in 1993-94 with the purpose of
closing the cracks and stopping water leakage. It has been found that the gradual increase of the tun-
nel length has stopped as a consequence of installing these cables. However, the post-tensioning ca-
bles were not able to eliminate water leakage and crack injections have been undertaken yearly to re-
duce the water leakage.
A major repair, where corroded reinforcement and concrete was removed up to a depth of 200mm and
replaced with new reinforcement and concrete, was carried out in the tunnel ceiling in the late 1990's.
This repair was subsequently strengthened with anchors in 2010 as delamination between the repair
and original concrete took place sometime after the initial reinforcement/concrete replacement.
General Basis of Assessment
The structural safety of the tunnel in the ultimate limit state (ULS) has been assessed in the two main
load bearing directions, the longitudinal and transverse direction in accordance with the Eurocodes.
The governing loads include self-weight of the tunnel, back fill, erosion protection, sedimentation, set-
tlement, water pressure, pre-stressing and temperature.
It has been previously assessed that the large settlements of the tunnel are mainly due to creep settle-
ment within the sand fill below the tunnel.
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Structural Assessment – Longitudinal Direction
The behaviour of the tunnel in the serviceability limit state (SLS) has been assessed to verify stresses
and crack widths and to check if an explanation can be given to why leakage is still observed in the
tunnel after the 1993-94 installation of the post-tensioning cables.
The analyses for the SLS case have indicated that there are tensile stresses in the longitudinal direc-
tion in the top and bottom slab resulting from the settlement recorded in the year 2017. The 1993-04
post-tensioning project has therefore not been successfully in fully closing the existing cracks and
keeping the tunnel structure in compression. For the load case with the predicted future increase in
settlement in the year 2069, the tensile stresses will increase further. It is therefore expected that wa-
ter leakage and the requirement for the injection of leaking cracks will continue if no other measures
are taken.
The global bending moment and shear capacity for the ULS case in the longitudinal direction have
been evaluated together with ULS shear capacity at the vertical construction joints in the tunnel. In ad-
dition, the ULS capacity of the bearings and piles at the northern end of the tunnel has been evalu-
ated. The evaluation analyses have been carried out for both the predicted future settlement during
the next 50 years and for an additional 50%. The capacity evaluation has in general shown that the
tunnel has adequate structural capacity in the longitudinal direction with satisfactory margins to carry
the increased stresses induced by the predicted future settlements.
The structural capacity of the tunnel has also been preliminary checked for the accidental load with a
water filled tunnel. The tunnel is expected to survive this accidental load with some damage, which will
need to be assessed and repaired after removal of the water.
Structural Assessment – Transverse Direction
It has been verified through a simple a 2D frame model that the tunnel has adequate ULS bending
moment capacity and that crack widths in general are below the maximum allowable crack width for
loads carried in the transverse direction.
A more advanced method has been used to analyse the overall combined ULS shear and bending
moment capacity in the transverse direction as it was not possible to verify ULS shear capacity with
the simple 2D frame model. This approach follows explicitly the crack development until a total col-
lapse of the tunnel is found at a given load. The results of the analysis have concluded that for the
ULS case the structural capacity is satisfactory for the tunnel structure in the transverse direction.
The structural capacity of the interface shear between the repair and the original concrete has been
reassessed as being satisfactory. This was used as the basis to the structural assessment of the tun-
nel cross section in the transverse direction.
Structural Assessment – Overall Conclusion
Structural analyses have revealed that the ULS capacity of the tunnel complies with existing standards
for the settlements experienced up to 2017, for the predicted settlements to 2069 and even for a sce-
nario with an additional settlement allowance. It is therefore considered very unlikely that the tunnel
will exceed the ULS case in the next 50 years.
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Accidental loads related to shipping traffic that may affect the tunnel have been considered at a pre-
liminary/conceptual level. A preliminary risk assessment has been carried out considering possible
loads related to ships (i.e. sunken ship resting on the tunnel roof, grounding ship impact, dragged an-
chor engaging the tunnel sides and a dropped anchor on the tunnel roof). This assessment has veri-
fied that the annual frequency of accidental actions that may cause damage severe enough to
threaten life safety is in accordance with the applicable standards with the exception of a grounding
ship impact at the northern end of the tunnel. It is recommended that a more detailed investigation of
the grounding ship impact load scenario is carried out to assess if protective measures will be re-
quired.
Condition Assessment
Structural Assessment – Accidental ship Loads
A comprehensive physical condition assessment of the tunnel structure has also been carried out. The
main conclusions are summarised below:
The characteristic compressive strength of the concrete has been determined to be a mini-
mum of 40 MPa compared to the original requirement of 25 MPa.
The outer waterproofing membrane is found to have limited function and is unable to prevent
water ingress into the concrete structures.
Numerous cases of leaking water have been observed in core holes and break outs indicating
that the tunnel structures are heavily exposed to water ingress.
High chloride contents have been found in several samples. In other samples very low chlo-
ride contents have been determined.
No signs of significant corrosion of reinforcement have been observed during inspections.
Hence, it is considered that the reinforcement is generally in good condition.
The quality of the interface between the repair and the original concrete in the roof is as-
sessed to be adequate to effectively transfer the shear forces although delamination is seen in
some areas.
It is strongly recommended to keep the tunnel under increased observation by comprehensive
monitoring and inspection activities due to the high exposure to water ingress and significant
chloride contents seen in some areas of the tunnel.
Basic Maintenance and Repair Strategy
Major repairs of the tunnel are not considered to be necessary within the next 10-15 years if the moni-
toring and maintenance plan, which has been established is followed. The suggested monitoring plan
includes the logging of key parameters to ensure that adequate information will be provided of the tun-
nel behaviour in advance of it possibly exceeding the limits identified in the report without warning. Re-
medial actions have been identified which could be implemented if the tunnel behaviour exceeds the
specified limits.
Retrofitting Projects
The remedial actions include one geotechnical and two structural retrofitting projects.
The geotechnical retrofitting strategy comprises horizontal compensation grouting under the tunnel
structure. By adopting this method, it will be possible to provide controlled uplift of the tunnel and
thereby counteract future settlements. The compensation grouting operations will be undertaken from
cofferdams located outside the tunnel structure in the Limfjord and it can be undertaken without im-
pacting the operation of the tunnel.
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The preferred structural retrofitting project includes additional pre-stressing with the purpose to close
cracks and limit water leakage through the tunnel structure. The pre-stressing will be placed within the
structural clearance profile and outside the traffic clearance profile along the upper parts of the walls.
The alternative structural retrofitting project comprises replacing and lowering of the bearing blocks at
the northern end of the tunnel. This could potentially reduce the future settlements and reduce tensile
stresses / water leakage in the tunnel.
Costs
A 50-year budget has been developed which includes an allowance for the three identified retrofitting
projects
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2 Background and objectives
The existing tunnel link between Aalborg and Nørresundby, shown on
Figure 2.1-1,
is a highway tun-
nel crossing below Limfjorden with water depths ranging from 1 to 12 m along the tunnel line. The im-
mersed tunnel is a monolithic reinforced concrete structure that was constructed during the 1960’s and
it was opened for traffic by May the 6
th
, 1969. A more detailed description of the tunnel is included in
Section 4.
Introduction
Figure 2.1-1 Aerial view and location plan considering the tunnel between Aalborg and Nørresundby.
From the very beginning the tunnel was suffering leakages, especially in the middle section of the tun-
nel. The most probable reasons have been studied in earlier assessments and identified as primarily
due to the malfunctioning of the waterproofing membrane, observed from the very beginning. The con-
crete structure has not been designed / detailed to be watertight and crack width requirements may
not be met for watertight structures. Additionally, restrained axial deformations (in longitudinal direc-
tion), as well as settlements have resulted in tensile stresses leading to cracks in the concrete that fur-
ther contributed to the leakages. Some repair campaigns have been undertaken (Section 4.5) but
these did not provide the ultimate solution of stopping the leakages. Annual injection campaigns are
an ongoing requirement to manage the leakage issue. From a durability and operational point of view
this has becoming an increasing concern for the Danish Road Directorate.
Additionally, continued settlements of the tunnel have been observed since 1969, in the northern sec-
tion of the immersed tunnel reaching as much as 130 mm, which can be considered as substantial
(Section 4.6). This has given another reason for concern for the Danish Road Directorate.
To clarify the expected remaining lifetime of the tunnel, the Danish Road Directorate established a Ge-
otechnical Expert Group and a Structural Expert Group, to further analyse the issues described above.
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The Geotechnical Expert Group acted in the period of May 2017 to April 2018 under the mandate of
identifying the reasons for the observed settlements and predicting additional settlements until 2069
corresponding to 100 years after tunnel opening. Creep of the uncompacted sand fill below tunnel ele-
ments IV and V was found to be the main contributor to the continued settlements and additional set-
tlements of up to 60 mm from 2017 to 2069 was predicted. The Structural Expert Group worked under
the mandate of:
Describe a long-term maintenance plan and outline one or more retrofitting project(s).
The retrofitting project(s) shall be described both technically and economically, and the influ-
ence on traffic flow/capacity during the implementation of the project(s) shall be evaluated.
The objective of the work of the Structural Expert Group, summarized in the underlying report, is to
provide the Danish Road Directorate with suitable and practical guidance as to maintain and repair
(where relevant) the structures of the Limfjord Tunnel for the remaining lifetime of the tunnel to year
2069. The Structural Expert Group has therefore provided:
A maintenance plan that identifies suggested surveys of the tunnel (when to measure what).
Trigger values that link the measurements from the maintenance plan to possible actions that
should be initiated to mitigate if the measurements reveal an unexpected behaviour.
An unexpected behaviour may cause repair / retrofitting projects to be considered.
The summary report and the background documents will allow the Danish Road Directorate to select a
cost-efficient strategy depending on the future development of the various scenarios.
The assumptions and conclusions from the underlying summary report and the background reports
are supported by all members of the Structural Expert Group.
The Structural Expert Group comprises:
Michael Gavins (Atkins)
Michael Tonnesen (COWI)
Carsten Schjørring (Christensen & Essenbæk)
Nhut Nguyen (Delta Marine Consultant)
Niels Mortensen (nmGeo)
Hans Henrik Ebsen Christensen (Rambøll)
Lars Knud Lundberg (Rambøll)
Hans de Wit (TEC)
The group was supported by:
Dorthe Lund Ravn (COWI)
Finn Raun Gottfredsen (COWI)
Peter Møller (Rambøll)
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The Structural Expert Group started their work in May 2018 with a meeting in which the Danish Road
Directorate explained the group's tasks and objectives and the Geotechnical Expert Group explained
the main findings of their work.
A brainstorm meeting on how to organize the work of the Structural Expert Group was carried after a
visit to the Limfjord Tunnel in June 2018. The work was organized into two subgroups, 1) A geotech-
nical sub group with focus on the geotechnical assessment and geotechnical input to the structural as-
sessment and 2) A structural subgroup with focus on the structural assessment and the condition as-
sessment. This is illustrated in a work organization flow chart in
Figure 2.2-1.
Methodology
Figure 2.2-1 Work organization flow chart
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The interaction between the geotechnical, structural and condition assessment is shown in the deci-
sion flow chart in
Figure 2.2-2.
The work started with review of relevant project information including as built documents and various
previous condition assessments and data reports. Indicative structural analyses were initiated with the
purpose to get an overview and to identify potential critical areas, which will serve as one of the focus
areas of the condition assessment.
The identified critical areas were analysed in detail with input from the condition assessment. The out-
come of the detailed analysis and further detailing of the indicative analysis plus results from the con-
dition assessment provided the basis for the Basic Maintenance and Repair Strategy and for the iden-
tification of geotechnical and structural retrofitting options.
Figure 2.2-2 Decision flow chart
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3 References
Normative references
[1]
[2]
[3]
Eurocodes including Danish national annexes (DK NA)
Handbook, Design Guide for load and calculation basis for bridges (includes supplemen-
tary rules for existing structures), April 2015
FIB Model Code for Concrete Structures, 2010
Background documents from The Structural Expert Group and Geotechnical Expert Group, which are
used as basis for the Technical Summary Report are listed below.
Geotechnical Expert Group Reports:
[4]
Geotechnical aspects considering settlements of the Limfjord tunnel. The Danish Road Di-
rectorate, May 2018
Background documents
Structural Expert Group Reports:
[5]
[6]
[7]
[8]
[9]
[10]
[11]
[12]
[13]
[14]
[15]
[16]
[17]
[18]
[19]
Geotechnical Summary Note, nmGeo-2019-07-Rev 2.1, 25-06-2019 (nmGeo)
Geotechnical Retrofitting Options – Final, TN02-Rev C, 25-06-2019 (Atkins)
Geotechnical Retrofitting – Compensation grouting solution, TN03, 25-06-2019 (Atkins)
Design Basis, Rev 2, 25-06-2019 (Rambøll)
Longitudinal indicative analyses including appendices, Ver 2, 25-06-2019 (Rambøll)
Structural Retrofitting Strategies – Pre-screening of Options, Description of selected Ret-
rofitting Options, 25-06-2019 (Rambøll)
Longitudinal indicative analyses – Beam model, A110235-SAN-02-002-Ver 2, 25-06-2019
(COWI)
Limfjord tunnel transversal section forces, Analyses of Transverse Properties, BIC-10-R-
00001-R.T.-Rev B, 25-06-2019 (BAM/TEC)
Assessment of transverse design of the Limfjord tunnel, EF1097/SvA/JV/R190024-Ver B,
18-06-2019 (TEC/BAM)
Non-Linear FEM analysis, EF1097/HDW/JV/R190034-Ver-2.1, 21-06-2019 (TEC)
Shear Capacity of Casting Joints in top slab, Calculation Report, A110235-SAN-01-010-
Ver 2, 25-06-2019 (COWI)
Shear Capacity of Casting Joints in top slab, Summary Report, A110235-SAN-01-011-Ver
2, 25-06-2019 (COWI)
Ship Accidents Risk Analysis, A110235-SAN-05-002-Ver 2, 25-06-2019 (COWI)
Basic Maintenance and Repair Strategy, A110235-REP-02-002-Ver 1, 25-06-2019 (COWI)
Condition Assessment, A110235-REP-01-001-Ver 1, 25-06-2019 (COWI)
Other Reports:
[20] Risikoanalyse – Limfjordstunnel, 16/02058-26, 03-06-2019, (Danish Road Directorate)
[21] Limfjordstunnelen – Trafikale Konsekvenser, 16/02058-25, 15-05-2019, (Danish Road Di-
rectorate)
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[22] Vurdering af effect af brandbekæmpelse – Cost-benefit analyser FTUN/GTUN/LTUN – Rev
1, 31-12-2014 (Rambøll)
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4 Description of tunnel
The tunnel was constructed in the late 1960´s and opened to traffic in 1969. It has two tubes each 12
m wide and each with three lanes for vehicles.
The tunnel structures are in total 945 m and are divided in three main groups:
The southern approach ramp (156 m), southern portal building (14 m) and cast-in-situ tunnel
(43 m).
The immersed tunnel consisting of five tunnel elements, I, II, III, IV and V each 102 m (total
length 510 m).
The northern approach ramp (207 m) and northern portal building (15 m).
The tunnel alignment is placed at a depth that allows a 139 m wide and 10 m deep navigation channel
over a part of the immersed section of the tunnel. The southern portal building is located on land ap-
proximately 220 m behind the oil harbour quay wall, whereas the northern portal building is located in
the fjord in a distance of approximately 150 m from the original coastline. The immersed tunnel is ex-
tending approximately 160 m under the harbour area behind the quay wall on the southern shore.
Structural layout
Figure 4.1-1 Areal photo of the Limfjord crossing.
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Figure 4.1-2 Longitudinal section of ramps, portal buildings, cast-in-situ tunnel and the five immersed tunnel elements.
The five tunnel elements are in the longitudinal direction straight as the curves of the vertical align-
ment of the road are formed in the ballast concrete placed after immersion.
The immersed tunnel and the cast-in-situ tunnel is one 553 m long monolithic reinforced concrete
structure separated from the portal buildings by expansion joints. The tunnel is furnished with a 1 – 2
mm thick butyl membrane on the outside, which on top and bottom of the tunnel is protected by a layer
of reinforced concrete.
Figure 4.1-3 Elastomeric bearing at the northern portal building.
The northern ramp and portal building are supported by piles, whereas all the other structures are di-
rectly founded on limestone, clay or sand fill. The northern end of the immersed tunnel is resting on
elastomeric bearings carried by the northern portal building.
The safety against uplift for the immersed tunnel is minimum 1,05 considering the most unfavourable
circumstances and without taking friction in the sand into account.
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Figure 4.1-4 Typical cross section of tunnel under the fjord.
The soil conditions in the area are characterised by limestone down to a significant depth. Above the
limestone layer is a layer of clay till of varying thicknesses. To the south, the clay till layer is close to
the terrain while to the north it is at a considerably lower level. The clay till layer in the area around the
oil harbour quay wall is covered by a layer of late glacial Yoldia clay. On the remaining sections, the
clay till layer is covered by meltwater sand above which is a layer of gyttja.
The southern ramp, southern portal building and cast-in-situ tunnel are constructed on a layer of
gravel placed directly on the limestone.
The elements of the immersed tunnel are resting on an approximately 1 m thick layer of sand installed
after immersion by use of the C&N sand jetting method. This sand layer is in the southern end resting
on limestone or clay till and in the northern end on a sand filling with a thickness of up to 20 m in-
stalled after dredging and removal of the gyttja.
Tunnel element I and the southern half of element -II have their foundations directly on the limestone.
From around the middle of element II near the oil harbour quay wall line and towards the north there is
a sandy clay till layer above the limestone upon which the northern half of element II is placed. The
thickness of this clay till layer is approximately 7 m.
At element III, a layer of Yoldia clay is situated above the clay till layer upon which the southern end of
element III is placed. From the northern half of element III and all of the elements IV and V, the gyttja
has been replaced with sand filling. The gyttja replacement has been continued to just north of the
northern portal structure. The thickness of the sand filling layer increases from south to north from ap-
proximately 2 m to approximately 20 m.
The replacement of gyttja has been performed with a width equal to a slope a = 0,5 from the edges of
the underside of the tunnel. The dredging of the gyttja has been performed as a trench with slopes
equal to a = 1,0 – 1,5. This is shown on
Figure 4.3-2.
Soil conditions
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4.3.1 Earth works
The dry dock with space for casting the five tunnel elements was constructed approximately 10 km
from the tunnel alignment. The bottom of the dock was at level -9,5 m and the groundwater level was
lowered to execute a dry excavation.
The southern ramp, southern portal building and the cast-in-situ tunnel were constructed in a dry pit
excavated behind the oil quay wall. The ground water level was temporarily lowered, but only until the
execution of the wet dredging of the tunnel trench were taking place. On the northern shore the con-
struction of ramp and portal building were executed in a dry pit created by construction of a dam and
cut-off wall and groundwater lowering.
Construction method
Figure 4.3-1 Dry pit at northern shore for casting of in-situ tunnel, portal building and ramp.
The wet excavation of the tunnel trench was executed with a bucket dredger. The slopes of the trench
were approximately 1:1,3 and the maximum depth approximately level - 31 m. The gyttja under the
northern section of the tunnel was dredged and replaced by an uncompacted sand filling executed by
pumping the sand from a dredger through a pipe with an outlet under water. A pre-loading of the sand
filling was created by placing a temporary approximately 2 m thick extra layer of sand above the actual
filling. The thickness of 2 m refers to sand surface next to the tunnel.
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Figure 4.3-2 Cross section in tunnel trench where gyttja was replaced by a sand filling.
After installation of the tunnel elements the trench was backfilled with sand. In the fjord the sand on
the sides of the tunnel was protected by a 1 m thick layer of stones.
Figure 4.3-3 Cross section in tunnel trench, southern end (under quay area).
Figure 4.3-4 Cross section in tunnel trench under the fjord.
Figure 4.3-5 Cross section in tunnel trench at the northern portal building.
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4.3.2 Concrete works
The ramps, portal buildings and the cast-in-situ tunnel were constructed as traditional reinforced con-
crete structures; the ramps in sections with expansion joints at every approximately 14 m.
The five tunnel elements were cast in the dry dock in special casting sections arranged to attempt to
compensate for the effects of shrinkage. The elements were cast in 12,8 m long sections; first the bot-
tom slab, then the walls and finally the top slab. The period between castings was maximum 3 weeks.
The sections were separated by 1,8 m long openings, which were cast as late as possible to achieve
maximum shrinkage of the 12,8 m long sections.
Figure 4.3-6 Casting of tunnel elements in the dry dock. The casting sections and openings can be seen on top picture.
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Ten different types of concrete mixes were used in the various tunnel structures including concrete
piles. The concrete mix for tunnel elements had a minimum average cylinder strength of more than
300 kg/cm
2
and the binder was standard Portland cement. The fine aggregates were natural sand and
coarse aggregates were either crushed granites or sea materials.
Reinforcement was in general weldable rebars with a minimum yield strength of 4200 kg/cm
2
. The
maximum crack width was not allowed to exceed 0,25 mm.
4.3.3 Installation of elements
Each tunnel element had at both ends a steel end frame extending along the entire outer perimeter.
On the steel end frame at the south end a Gina type rubber gasket was attached.
After outfitting of the elements in the dry dock with water ballasting tanks and pump systems, bulk-
heads, bollards, access shaft and the rubber gasket, the dock was flooded. The tunnel elements were
ballasted to remain on the bottom of the dock during and after the flooding.
At the same time as the last section of the tunnel trench was excavated, a channel into the dry dock
was dredged. The tunnel elements were then one by one floated and transported by use of tug boats
the approximately 10 km distance from dry dock to the tunnel alignment. At the tunnel site they were
prepared and equipped for the immersion operation. Two catamaran immersion pontoons were used
for the immersion. The elements were installed one by one from south towards north.
After immersion the tunnel elements were temporarily supported in three points. One support was cre-
ated by a console extending from the middle wall resting on the adjacent element/structure to the
south. The two other supports were arranged on temporary gravel pad foundations at the northern end
of the element. The correct vertical alignment was secured by use of jacks installed at all the tempo-
rary supports.
Watertight immersion joints were initially established by the rubber gasket attached to the south end of
each tunnel element. As soon as the space between the two bulkheads of the elements to be con-
nected was drained the rubber gasket was compressed between the end frames of the two adjacent
elements.
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Figure 4.3-7 Immersion of tunnel element onto temporary supports.
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4.3.4 Joints
A secondary watertight seal was installed on the inside of the primary Gina type gasket. This seal was
a flat rubber seal bolted to the end frames of the elements.
On the inside of gasket and seal recesses were made to allow the casting together of the elements.
The rebars were connected by installation of additional pieces of rebars butt welded to the rebars ex-
tending from both elements.
Figure 4.3-8 Immersion joint. The joint shown is between elements III and IV where additional reinforcement was in-
stalled due to the not perfect alignment.
This type of joint was used to connect the cast-in-situ tunnel with element I and to connect elements I,
II, III, IV and V. Between the element V and the south end section of the northern portal building a clo-
sure joint was cast inside a temporary watertight enclosure.
The joints created a monolithic tunnel structure from the cast-in-situ tunnel to the northern portal build-
ing. Available information indicate that the immersion joints have all been successful as in general no
water leakages have been reported in connection to the joints.
Figure 4.3-9 Closure joint. Located between Element V and south end section of the northern portal building
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4.3.5 Waterproofing membrane
The 1 – 2 mm thick butyl membrane was installed on the outer surface of the tunnel structures to en-
sure the watertightness of the tunnel.
On the bottom and top of the tunnel elements the membrane was protected by a layer of reinforced
concrete.
In the fjord the protection on the top is approximately 200 mm thick and in the quay area to the south
approximately 50 mm thick. In the entire area the protection with reinforced concrete at the bottom is
approximately 60 mm thick. Before installation of the reinforcement for the tunnel bottom slab a 30 mm
thick layer of unreinforced concrete was placed on top of the membrane as a protection from the rebar
works.
Figure 4.3-10 Protection of membrane at the bottom of tunnel elements (Dimensions are shown in cm).
On the sides of the tunnel elements there was no protection and available information indicates that
already during transport and immersion some damages occurred on the unprotected membranes on
tunnel sides. Further is has been indicated that the adhesion of the membrane to the structures was
not perfect.
It is a fact that the membrane failed to create the watertight structure as was intended.
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Figure 4.3-11 Protection of membrane at the top side including the top corner of tunnel elements (Dimensions are
shown in cm).
Early defects
4.4.1 Leakage
Leakages were observed already immediately after installation of elements. The leakages continued
to occur also during the start of operation.
As the damages on the membrane during transport and immersion were assumed to be the main rea-
son for the leakages, attempts were made to repair these damages before the backfill made such re-
pairs impossible. Available information indicates that the repairs executed by divers and under water
were not successful.
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The leakages occurred mainly in or around the 1,8 m wide openings cast after the 12,8 m wide main
sections. They were also concentrated in the top slab sections of elements II, III and IV.
Figure 4.4-1 Water Leakage at the short sections (Dimensions are shown in mm)
The leakage was observed through already existing early-age and shrinkage cracks in the tunnel roof
and outer walls.
The situation that the tunnel was not watertight had an impact on the operation, as the leakage water
was apparent to the users, creating some (not relevant) anxiety regarding the safety of the tunnel and
some practical problems due to the sometimes, heavy inflow of water.
Further the comprehensive occurrence of leakages caused the concern that they would influence the
durability of the tunnel, i.e. shorten the operational lifetime of the structure.
4.4.2
Settlement and deformation monitoring
The settlements of the tunnel elements were measured and recorded on a regular basis and these
settlements were considerably bigger than the maximum few cm foreseen in the original design.
Further the yearly movements at the expansion joints of both ends of the monolithic tunnel due to the
seasonal temperature variations have been monitored and recorded. The movements have not been
completely cyclic as the structure has increased its lengths with small increments over time.
4.5.1 Background
The high rate of the settlements not foreseen in the design continued over the years and showed al-
most no signs of decreasing.
The many and continuing leakages of salt water from the fjord through the outer walls and top slab of
the tunnel and the significant exposure of the inside surfaces of the tunnel to salt water sprays from
de-icing salts on the roads, caused reinforcement corrosion and resulted in a need for comprehensive
Repair and strengthening works
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concrete repair works after a period of 25 – 30 years. Example of reinforcement corrosion as recorded
from an inspection in 1988 is shown on
Figure 4.5-1.
Figure 4.5-1 Reinforcement corrosion from inspection in 1988.
Already at that time – with a traffic intensity much lower than today – it created a difficult traffic situa-
tion when the necessary concrete repair works closed a tunnel tube during a year and all traffic had to
be ducted through the one remaining tube.
It was concluded that the problems were caused by the combination of a defect membrane, tempera-
ture variations in the monolithic structure, the unexpected big settlement rates and other circum-
stances regarding support conditions. Investigations were made, and proposals developed regarding
how to compensate or eliminate the negative circumstances.
As result of these investigations it was decided to strengthen the tunnel structure to reduce or elimi-
nate the cracking – and thereby reduce or stop the leakages and at the same time improve the carry-
ing capacity in the longitudinal direction.
4.5.2 Activities (1990 – 2018)
The following major repair and strengthening projects were executed:
Tensioning of the tunnel cross section with cables installed in the ballast concrete: 1993 –
1994.
Repairs of sections of ceiling and walls and installation of tiles on walls: 1995 – 1998.
Fire protection of structures: 1998 – 1999.
Fixing of delaminated concrete with adhesive anchors: 2010 – 2011.
Replacement of parts of ballast concrete and wearing course: 2012.
Crack injections: Continuously (detailed records from the period 2008 – 2018).
Repairs in northern joint chamber: 2007 and later.
In addition to above activities mainly covering the immersed section of tunnel there have been exe-
cuted repairs on remaining structures such as the ramps.
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The tensioning of the tunnel with post tensioning cables installed in the ballast concrete in 1993-94
was carried out with the purpose to reduce the longitudinal tensile stresses and close through going
cracks and thereby limit/stop water leakage. The Ultimate Limit State (ULS) structural capacity in the
longitudinal direction was increased due to the additional post tensioning cables and thereby increas-
ing the robustness of the tunnel. The location of the post tensioning cables is shown on
Figure 4.5-2.
The deformations of the tunnel due to the seasonal temperature variations resulted, before the ten-
sioning of the tunnel cross section, in a slow increase of the tunnel length corresponding to approxi-
mately 1 mm per year. After the installation of the cables in 1993 – 1994 the yearly increase in length
has in general been stopped.
Figure 4.5-2 Typical cross section with post tensioning cables installed in ballast concrete in 1993 – 1994.
A large part of the 1998 repaired concrete in the tunnel ceiling was retrofitted in 2010 - 2011 with ad-
hesive anchors between the repair and original concrete as delamination was observed between the
repair and original concrete. This retrofitting inclusive a reassessment of the structural capacity of the
repaired section is described in Section 7.5.5.
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Figure 4.5-3 Installation of adhesive anchors in tunnel ceiling to make a structural connection between repair concrete
and original concrete
4.5.3 Current activities
Since the above listed repair and strengthening activities the monitoring and maintenance of the tun-
nel has been less intensive.
Crack injection campaigns
Cracks and leakages occur every year when the temperature drops and the tunnel structure contracts.
Crack injection campaigns are therefore executed every winter on almost regular basis. The crack in-
jections are possible during late evenings and nights when one tunnel tube can be closed for traffic
without creating serious restrictions for the traffic. The impact on the flow of traffic is minimal as the
tunnel can be kept completely open during daytime and rush hours.
Figure 4.5-4 Injection of leaking cracks
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Other activities
As in case of the crack injections other maintenance works – e.g. on E & M equipment - are at present
executed during evenings and nights.
An exchange of Omega seal in the northern joint chamber is at present planned/ongoing, but this work
can be executed without restrictions for the traffic in the tunnel.
The investigations of the condition of the tunnel structures, reported in the following Section 6 of this
document, have in general been possible during evenings and nights and during the periods where a
tunnel tube already has been closed due to maintenance works.
As explained above the leakages occurred already immediately after the construction of the tunnel,
but at the same time some not expected big settlements started, and they have continued and show
no signs of decreasing.
Recorded settlements
Figure 4.6-1 Recorded settlements during the period 1969 – 2017.
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5 Geotechnical assessment
The overall conclusions from the geotechnical expert group have been described in the background
document and are summarised below.
Figure 5.1-1
illustrates:
The location of tunnel elements along the alignment. The elevation of the tunnel elements re-
fers to the right y-axis.
The excavation level to which Gyttja was removed and replaced by sand fill.
Observed settlements per December 2017 are also included for both tubes. The measure-
ments refer to the left y-axis.
Summary of results, geotechnical expert group
Figure 5.1-1 Tunnel elements along the alignment together with lower boundary for infilled sand.
Figure 5.1-2
is based on
Figure 5.1-1.
The blue curve represents the thickness of sand fill below the
tunnel base (right y-axis), while the normalised settlements (red curve, left y-axis) represents the
measured settlements from
Figure 5.1-1
divided by the thickness of the sand fill.
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Figure 5.1-2: Thickness of sand fill below tunnel base and normalised settlement of tunnel as per December 2017.
Figure 5.1-2
shows that the normalised settlements are almost constant along the part of the tunnel
being placed on sand fill, and this observation served as the working thesis for the geotechnical expert
group during the project period.
The submerged weight of sand fill is approximately twice that of the replaced Gyttja, so pumping in
sand has caused an increased weight on the excavated base. The almost constant value of the nor-
malised settlements along the sand fill part of the alignment implies two possible mechanisms:
Settlements are caused by the increased weight from sand fill on the excavated base, and set-
tlements will therefore originate from strata deeper than elevation -31 m, or
Settlements are caused by settlements within the sand fill itself, i.e. above elevation -31 m.
Information from previous site investigations was combined with data from a series of boreholes and
CPTs (Cone Penetration Testing) conducted in 2017 and assessed, the overall findings were:
Placing sand fill within the excavated trench may have given rise to settlements within the in-
tact deposits on
Figure 5.1-1
of the order of 10-20 mm, but these settlements must have been
fully developed before the tunnel was placed. Settlements within the tunnel can therefore not
originate from the deeper strata.
Samples of sand fill from the 2017 borehole campaign were tested within the geotechnical la-
boratory using oedometer testing with a 100 mm diameter oedometer ring. The sand fill was
placed within the oedometer ring by under-water pouring to recreate the depositing history.
The testing revealed that the stiffness of the sand fill was significantly lower than originally as-
sumed during design in the 1960s.
Full scale observations from sand fillings abroad revealed that loose and uncompacted sand
fill will creep meaning that the material will keep settling for a considerable time.
The creep behaviour will likely be amplified as the Gyttja below the sand fill adjacent to the
tunnel, cf.
Figure 5.1-3
, will continue to consolidate in in the long term (50 years or more)
causing the sand around the tunnel to continue to settle.
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Figure 5.1-3 Cross-section of back-filled tunnel.
The tunnel was placed in an excavated trench and sand was subsequently back-filled around the tun-
nel. Loading on the walls and on the base / top of the tunnel will therefore be influenced by soil and
water pressures. Soil reactions have been summarised in the background document
Geotechnical
summary note
[5] comprising:
Soil springs simulating the effect of normal and shear stresses acting on the concrete faces of
the tunnel. The spring stiffness has been estimated together with the maximum force within
the spring following a linear elastic, ideal plastic approach. Recommendations are given con-
sidering the direction of the frictional force between the soil and the concrete faces.
Pile capacities and axial pile stiffness for the driven concrete piles placed below the northern
portal structure.
An estimate of the extent of a possible void where the northern part of element V may have
lost contact to the sand fill below the element.
Various aspects considering different retrofitting scenarios.
Input to structural assessment
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6 Condition assessment
This section contains a summary of the comprehensive condition assessment of the Limfjord Tunnel
carried out in 2018 and 2019 as described in [19].
In order to carry out the structural calculations on the best possible basis it was decided to determine
the actual strength of the original concrete based on cores from the tunnel. The testing was designed
so that it could take into account possible differences in concrete quality between the different tunnel
elements (as these have been constructed at different times) and between the different structural parts
of the individual elements.
Coring has only been conducted on tunnel elements II, III and V as most of the challenges associated
with the tunnel are linked to these three tunnel elements.
Further to compressive testing, condition assessment has been carried out on different parts of the
Limfjord Tunnel as summarized in
Table 6.1-1.
Compressive
tests
HCP measure-
ments
Cores (Macro
and micro
analyses)
X
X
X
X
X
X
X
X
X
X
X
X
Chloride
content
X
X
X
X
X
X
X
Water
content
Introduction
Structural element
Break outs
Top slab - outside
Top slab - inside
Outer walls
Inner wall
Bottom slab
Table 6.1-1 Overview of tests included in the condition assessment.
From
Table 6.1-1
it is clear that the condition assessment is quite comprehensive. The condition as-
sessment has focused on the following subjects:
level of corrosion of the reinforcement (based on chloride content, water/moisture content,
HCP measurements, break outs and cores),
risk of delaminations (from cores),
quality of structural concrete and repair concrete (based compressive tests, macro and micro
analyses),
signs of problems with overload and corrosion of welded rebars at immersion joints and clo-
sure joint (from visual inspection and break outs),
condition of fire protection (from cores and visual inspection).
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Figure 6.1-1 A concrete core from the roof has been cut in half in order to prepare for extraction of two thin sections
(T).
Figure 6.1-2 Cores extracted from wall (cores without fire protection) and roof (cores with fire proofing).
The cores have been grouped in nine different groups. Firstly, by tunnel element (II/III/V), secondly by
type of casting section (long/short)
1
and thirdly by structural part (wall/top slab). For each of these
groups the characteristic in-situ compressive strength was determined.
The grouping of cores as well as the number of cores in each group can be found in
Table 6.2-1
,
showing a total of 43 tested cores.
Compressive strength
1
The meaning of long and short (casting) section is described in section 4.3.2.
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The determined compressive strengths are also given in
Table 6.2-1
. It should be noted that the mini-
mum average compressive strength of 300 kg/cm
2
originally required with nowadays terms corre-
sponds to a characteristic strength of C25/30.
Table 6.2-1
shows that the compressive strength deter-
mined in this project is significantly higher than the originally required strength.
Group
No. of
cores
4
5
4
6
5
4
6
5
4
43
Characteristic in-situ
compressive strength
[MPa]
47,9
39,9
45,6
50,0
49,5
53,5
50,8
45,4
47,8
48,6
Indicative Compressive
strength class
C45/55
C35/45
C45/55
C50/60
C45/55
C50/60
C50/60
C45/55
C45/55
C45/55
Element II - Long section, Top slab
Element II - Long section, Walls
Element II – Short section
Element III - Long section, Top slab
Element III - Long section, Walls
Element III – Short section
Element V - Long section, Top slab
Element V - Long section, Walls
Element V – Short section
All cores grouped (weighted average)
Table 6.2-1 Calculated characteristic in-situ strength based on the assumption of a "known" coefficient of variation of
0,13. The corresponding compressive strength class according to DS/EN 206 is also shown.
6.3.1 Outer part
Three aspects of the outer parts of the top slab have been of particular interest:
The protective concrete (Integrity/Corrosion)
The waterproofing membrane (Integrity)
The condition of the outer reinforcement (Corrosion)
In order to investigate these topics, it was planned to take out 15 cores from the outside of the tunnel.
Due to considerable practical problems related to the coring, only five cores were collected. The five
cores, each with three layers (protective concrete, waterproofing membrane and structural concrete)
have been analysed by macro- and micro analysis, supplemented with measurements of the chloride
content. The cores are shown in
Figure 6.3-1
together with samples of reinforcement collected to-
gether with the cores.
Figure 6.3-1
indicates that it was not possible to collect intact cores, which is assessed to be related to
the difficult coring conditions and not the concrete quality. Generally, the protective concrete is seen at
the top of the cores while the structural concrete is seen at bottom of the cores. The membrane can be
seen between the two concrete layers in four of the five cores.
Top slab
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Protective concrete layer: The concrete generally consists of materials of good quality. Some alkali sil-
ica reactive particles have been observed but no damaging reactions have been observed.
The chloride content of the concrete is higher than 0,3 % chloride (by weight of concrete) throughout
the layer. The rebars do not show any significant signs of corrosion despite the high chloride content.
This is most probably due to lack of oxygen. Pitting corrosion cannot be excluded, but no signs have
been observed. Generally, the risk of pitting corrosion is assessed to be low.
Core UA1
Core UA2
Core UA3
Core UB4
Core UD3
Figure 6.3-1 The five cores taken from the outside of the Limfjord Tunnel. The cores were taken from three different
areas UA, UB and UD.
Waterproofing membrane: No signs of adhesion to either the underlying structural concrete or the pro-
tective concrete above have been observed. The membrane appears intact but has no to limited adhe-
sion between the individual membrane layers.
Structural concrete layer: The concrete generally consists of materials of good quality, but some reac-
tive particles have been observed. Some ASR-gel is present in cracks and voids, but no damaging re-
actions have been observed.
The chloride content appears high (between 0,16 and 0,78 % by weight of concrete) near the exposed
surface (membrane side). A chloride content above the threshold value (0,1 % by concrete weight) is
seen at reinforcement level. The rebars do not show any significant signs of corrosion despite the high
chloride content. This may be due to lack of oxygen. Pitting corrosion cannot be excluded, but no
signs have been observed.
6.3.2 Inner part
The following major repairs have been carried out at the inside of the roof slab:
Repairs of major sections: 1995 – 1998.
Fixation of delaminated concrete (delamination between original and repair concrete) with adhe-
sive anchors: 2010 – 2011.
Due to the above repair works it has been of major interest to investigate the current condition of the
repair works. The following topics have been of particular interest:
Interface/cohesion between repairs and original concrete
Chloride content and water content
Corrosion (current level/risk of future corrosion)
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Interface/cohesion assessment
In relation to the testing of the compressive strength, 32 cores were taken out from the top slabs. For
each of these cores the interface between repair (if any) and original concrete has been assessed by
visual inspection. The results of the assessment are summarised in
Table 6.3-1.
Assessed condition of
interface
No repair
Fully intact (80-100%)
Partially intact (50–80%)
Poor (<50%)
Sum
No. of cores
[-]
15
7
10
0
32
Ratio
[%]
47
22
31
0
100
Ratio, repairs [%]
-
41
59
0
100
Table 6.3-1 Assessment of interface between repair and original concrete based on 32 cores taken from the top slab.
In some cores fine cracks were observed in the interface, leading to an assessment of the interface
being only partially intact – see example in
Figure 6.3-2.
The cracks will in some areas act as means
of transport of water longitudinally and transversely. This was observed in a number of holes left open
after the coring.
Figure 6.3-2 Core extracted from roof. The concrete is cracked both at the interface between repair and original con-
crete (red arrow) as well as within the original concrete (blue arrow).
From the above it is concluded, however, that the cohesion between the repair and original concrete is
of reasonable quality. The interface will be able to contribute to the transfer of forces between repair
and original concrete, which is a prerequisite for being able to consider the full section of the top slab
when calculating the bending moment and shear capacity – see Section 7.5.5.
Chloride content
Chloride content has been determined on five cores. The results show significant variation in the chlo-
ride content from core to core and also within the single cores.
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In three of the five cores the chloride content was determined as being below the threshold value of
0,10 % by concrete weight
The highest chloride content found in the remaining two cores was 0,12%, which is seen to be above
the threshold value of 0,10%.
Water content
The water content and the degree of water saturation have been determined on three cores. The wa-
ter content was found to be between 2,9 and 4,9 %. The degree of water saturation was found to be
between 77,6 % and 98,3 %.
Corrosion (current level/risk of future corrosion)
The current level of corrosion has been evaluated from Half Cell Potential (HCP) measurements and
break outs. HCP measurements have been carried out in five areas.
For the top slab, the HCP values and the deterioration of the fire protection are correlated:
In areas with deteriorated fire protection – due to water ingress over a long period – there are
low (i.e. more negative) HCP values, indicating a risk of corrosion (or higher water content in
the concrete).
In areas with intact fire protection – due to no or limited water ingress – there are higher HCP
values indicating limited risk of corrosion (or dry concrete).
Despite low HCP values in some areas, no corrosion was observed on the reinforcement – see exam-
ple in
Figure 6.3-3.
This is valid for all reinforcement examined in the cores – and all the break outs
performed on-site to calibrate the HCP measurements.
The HCP-measurements were supplemented with corrosion rate measurements. All measurements of
corrosion rate showed "very low" to "low" corrosion rate – again indicating a high probability of no sig-
nificant ongoing corrosion.
In areas with signs of water ingress (usually indicated by a lighter colour of the fire protection), water
was typically dripping from the original concrete shortly after break outs were established – even
though the surface seemed dry before the break outs.
In areas with no signs of major water ingress (dark colour of the fire protection) the original concrete
was dry in the break outs.
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Figure 6.3-3 HCP results from roof. The whole area was wet. No corrosion observed on reinforcement in break out de-
spite the very low potential (-600 mV). Investigated area at transition between element II (left - 3 m) and element III
(right – 17 m).
6.3.3 Fire protection
The fire protection layer on the soffit is deteriorating in some areas where it can be removed by hand.
It is assumed that the fire protection in these local areas no longer protects the concrete fully against
fire. These areas appear lighter in colour compared to areas with intact fire protection. It is assessed
that this is because salt crystals build up in the fire protection causing it to slowly peel off.
It is found that the deterioration is connected to the ingress of water, cf. previous section.
The level and extent of deteriorating fire protection has not been registered in detail but can be ob-
served from the cores taken in the roof.
Figure 6.3-4 Area where fire protection has deteriorated.
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For the outer walls the main concern is the level of ongoing corrosion as well as the risk of future cor-
rosion of the reinforcement. Corrosion may lead to delamination as was observed prior to the substan-
tial repairs of the walls in the late 1990's.
6.4.1 HCP measurements and break outs
HCP-measurements have been carried out in five areas on the outer wall of the eastern tube.
The HCP values measured in the wall – where this is covered with tiles – are high, indicating low risk
of corrosion. Break outs to the reinforcement showed no signs of corrosion.
The HCP measurements were supplemented with corrosion rate measurements. All measurements of
corrosion rate showed "very low" to "low" corrosion rate – again indicating a high probability of no sig-
nificant ongoing corrosion.
In areas with signs of water ingress, water was typically dripping from the original concrete shortly af-
ter break outs were completed – even though the surface seemed dry before the break outs. The re-
pair concrete, together with the tiles, seem to function as a waterproof layer keeping the water inside
the original concrete. In areas with no signs of major water ingress the original concrete was dry in the
break outs.
Despite the dry surface of the tiles and tile joints, water is also coming out from holes drilled for con-
crete dust samples or for making HCP measurements at the surfaces covered by tiles. This indicates
that the concrete behind the tiles is saturated with water.
6.4.2 Chloride content
From the inside of the eastern wall 15 chloride profiles have been determined.
In 4 different locations samples were taken in three different heights. In three of these 4 locations all
profiles showed chloride content well below the threshold of 0,10% (by weight of concrete). In the
fourth location the chloride content varied between <0,005 % and 0,17 %.
In
Figure 6.4-1
three chloride profiles determined from cores are shown. As can be seen from the fig-
ure, in a few instances (8 out of 54 samples) the chloride content is found to be above the threshold
value of 0,1 %.
6.4.3 Water content
The water content and the degree of water saturation have been determined on three cores. The wa-
ter content was found to be between 2,7% and 6,5 %. The degree of water saturation was found to be
between 77,3 % and 94,1 %.
Outer walls
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Figure 6.4-1 Chloride profiles from three cores taken from the inside of the eastern wall.
6.5.1 HCP measurements and break outs
A single area has been selected for HCP measurements at the same location where the lowest HCP
values were observed for the top slab and outer wall. The HCP measurements indicated no risk of cor-
rosion. Further to that, two break outs showed dry concrete and no signs of corrosion of the reinforce-
ment.
6.5.2 General condition
No chloride measurements were made from the concrete in the mid wall. Also, no measurements of
the water content were made. The concrete (both behind and above tiles) are assessed having a low
water content as the water exposure is low. Generally, the mid wall is assessed to be intact with no
ongoing deterioration.
Mid wall
A single core has been extracted to examine the ballast concrete and the upper 200 mm of the struc-
tural concrete in the bottom slab. No signs of deterioration were observed on the ballast concrete (old
and new) or in the concrete in the bottom slab.
6.6.1 Post tensioning cables
Two concrete cores were extracted from the concrete cast between the post tensioning cables – no
defects were observed. A single break out to a post tensioning cable and subsequent opening of a ca-
ble duct showed no signs of anomalies or deterioration. The concrete, the cable ducts, the injection
Bottom slab
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mortar and the strands were all without signs of deterioration and without deviations from specifica-
tions and drawings.
6.6.2 Chloride content
Chloride profiles have been determined from two cores taken from the bottom slab. The core B2 is
taken in the part of the bottom slab where the post tensioning cables are situated. The core B3 is from
part of the bottom slab/ballast concrete without post tensioning cables.
The chloride contents determined in the bottom slab are shown in
Table 6.6-1.
As can be seen from
the table, a number of the samples show chloride content above the upper threshold of 0,1 %.
Core
Concrete type
Distance "0" corresponds to:
Distance from surface / from membrane [mm]
0-10
10-20
0,02
20-30
<0,005
30-50
<0,005
50-70
<0,005
B2
Repair ballast
concrete I
Ballast concrete
Underside asphalt
0,19
B3
Casting joint between ballast con-
crete and structural concrete and up
in the ballast layer.
Casting joint between ballast con-
crete and structural concrete
0,17
0,11
0,10
0,06
0,02
B3
Structural con-
crete
0,10
0,15
0,13
0,13
0,10
Table 6.6-1 Chloride contents (by concrete weight) determined on three cores taken from the bottom slab.
The results in
Table 6.6-1
indicate that the primary route for chloride ingress is through the casting
joint between structural concrete and ballast concrete.
As the concrete cast between the post-tensioning cables is well described and tested during the re-
pair, it is assessed that significant chloride ingress is unlikely. This assessment is supported by the
chloride testing of core B2 where chlorides are only present in a significant amount in the upper most
10 mm.
Special attention shall however be given to various areas inclusive the construction joints at the an-
chorage zones of the post-tensioning system.
The immersion joints and closure joint have been given special attention. The main concern has been
the condition of the welded connections that secures the transfer of forces in the horizontal reinforce-
ment through the five normal immersion joints and the special closure joint between element V and the
in-situ build part of the northern portal structure. The layout of the two types of joint is shown in
Figure
6.7-2.
Immersion joints and closure joint
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Figure 6.7-1 Closure joint between Northern Portal (NP) and Element V (E5) before removing tiles and concrete in order
to inspect the reinforcement.
Immersion joint
(Type 1 joint)
Closure joint
(Type 2 joint)
Figure 6.7-2 Layout of immersion joints and closure joint.
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It was decided to concentrate inspections on the closure joint as this is the most critical joint. The inner
layers of the reinforcement were exposed by means of water jetting at a rather large part of the clo-
sure joint.
No signs of butt-welded reinforcement were found in the exposed area – see
Figure 6.7-3.
Instead nu-
merous traditional laps were found.
Figure 6.7-3 Exposed reinforcement at the closure joint (Type 2 joint). No signs of
butt-welded connections in the horizontal reinforcement.
It has not been possible to determine whether the butt-welds were never made or whether they have
been exchanged with laps during the repairs in the late 1990's. However, several photos taken during
construction have shown that butt-welds were made in some places with the specified "sharpening" of
reinforcement ends and subsequent butt weldings, see
Figure 4.3-8.
It is therefore quite possible that
the butt weldings were made as specified in the drawings.
All the exposed reinforcement – original and new – in both original and repair concrete was found to
be intact and with no major signs of corrosion. A few minor signs of corrosion of the reinforcement was
found – but all with no reduction of cross-sectional area.
The following main conclusions can be drawn in relation to the condition assessment of the Limfjord
Tunnel:
The characteristic compressive strength of the concrete has been determined to be a mini-
mum of 40 MPa compared to the original requirement of 25 MPa.
The outer waterproofing membrane is found to have limited function and is unable to prevent
water ingress into the concrete structures.
Numerous cases of leaking water have been observed in core holes and break outs indicating
that the tunnel structures are heavily exposed to water ingress.
Close connection between deterioration of fire protection and moisture ingress in roof is found.
Conclusions
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Delamination between repairs and structural concrete have been observed in some areas. It is
assessed that these delaminations will act as transport ways for water penetrating trough the
concrete from the outside.
High chloride contents have been found in several samples. In other samples very low chlo-
ride contents have been determined.
No signs of significant corrosion of reinforcement have been observed during inspections.
Hence, it is considered that the reinforcement is generally in good condition. The assessment
is that:
o
Repairs effectively protect reinforcement against corrosion.
o
Lack of oxygen prevents the corrosion of reinforcement in deeper lying parts of con-
crete sections as these are generally water saturated. This also goes for the outside
reinforcement. It should be noted, however, that for the outside reinforcement this is
only based on five cores.
It is assessed that the interface between repair and original concrete in the roof is of such
quality – irregular in surface and well-cast – that significant shear capacity is present. Based
on visual inspection of cores it is assessed that at least 50 % of the cross section may be ac-
counted for in shear.
Exposed reinforcement in the closure joint proved to be fully intact. Signs of major problems in
other parts of the joints (immersion joints and closure joint) have not been observed. Hence, it
is concluded that there are no immediate problems with the load bearing capacity of the joints.
It is strongly recommended to keep the tunnel under increased observation by comprehensive
monitoring and inspection activities due to the high exposure to water ingress and significant
chloride contents seen in some areas of the tunnel. See section 8 for further details on this.
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7 Structural assessment
This section describes the structural analyses carried out, the background / purposes, the assump-
tions and the results.
The analyses are divided into two groups:
1. Longitudinal analyses
2. Transverse analyses
Introduction
The overall purpose of the structural analyses is to verify that the structural safety is satisfactory for all
cross sections in both the longitudinal and transverse direction.
The purpose is also to analyse the effects in the longitudinal direction that causes the continuous leak-
ages and penetration of seawater, which has an impact on the operation and durability of the tunnel.
I.e. the yearly contraction of tunnel due to thermal actions (cooling) and the on-going settlements in
the northern end of the tunnel that increases the tensile stresses in certain areas of the tunnel.
Purpose
The verification is carried out in accordance Eurocodes including Danish national annexes for bridge
and “Handbook, Guidance on loads and basis of design, bridges”, which includes supplementary rules
for existing bridges. Interface shear between original and repair concrete in the roof has also been ver-
ified in accordance with FIB Model Code for Concrete Structures, 2010, which also is used as basis
for the non-linear elastic analyses carried out by Finite Element Model (FEM) Software DIANA.
The structure belongs to consequence class CC3, i.e. a K
FI
factor of 1,10 shall be applied to all unfa-
vourable loads.
The governing load combination is supposed to be (6.10a) – permanent loads dominating, see Table
A2.4 (B+C) DK NA in DS/EN 1990/A1 Annex A2 DK NA. For this load combination no variable loads
are considered. The partial safety factor on the unfavourable permanent loads is in this case 1,25. It
should be mentioned that buoyancy is considered as an integrated part of the total dead load of the
tunnel corresponding to an immersed “voided” beam, i.e. that the K
FI
× 1,25 = 1,38 shall be applied to
both the dead load and buoyancy of the tunnel. This corresponds to applying the same factors to the
water pressure when analysing the tunnel in the transverse direction. It should be noted that a partial
safety factor of 1,00 has been used for settlements.
Unit weight of the structural concrete is assumed to be 24,5kN/m
3
based on measurements done on
test pieces from cores taken out of the concrete structures as part of the condition assessment. Unit
weight of ballast is assumed to be 24 kN/m
3
.
On the resistance side, the partial safety factor for the original reinforcement FKF 42 (weldable ribbed
rebars, K), is reduced to
ϒ
S
=1,12 because this type of rebars was produced with a guaranteed yielding
strength of 410 MPa, assumed to correspond to 0,1% fractile value.
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The concrete compression strength has been measured in the laboratory for the drilled-out cores as
part of the condition assessment programme. Based on the results (groups of cores from different tun-
nel elements, and total number of cores) a compressive strength of 40 MPa (5% fractile value) can be
assumed in the capacity calculation of the concrete sections. The corresponding safety factor can be
reduced to
ϒ
C
= 1,45 ×0,95 = 1,38 because the tests have been made on cores from the actual struc-
ture, which is considered comparable to tightened control.
A more detailed description of the basic assumptions can be found in the Design Basis [8].
Accidental actions
Fire
Fire protection has been applied. A risk assessment with regards to installation of various fixed fire
fighting systems has been performed, but not as part of this project, cf. [22]. Follow-up activities on the
condition of the fire protection and on the risk assessment are outside the scope of this project.
Ship impact scenarios
A preliminary risk analysis of ship accidents has been carried out evaluating whether the annual fre-
quency of accidents causing damage severe enough to threaten life safety exceeds the annual ac-
ceptance criterion of 10
-5
per tunnel element, cf. [17].
The ship accident comprises impact scenarios such as sunken ship resting on the tunnel roof,
dropped anchor on the top of tunnel roof, dragged anchors and grounding ships. The tunnel elements
exposed to risk of ship accident are tunnel element II to V.
7.3.1
Figure 7.3-1 Representative Cruise ships at Limfjorden (top). Principle sketch of grounding ship (bottom).
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The analysis concludes that:
For elements II, III and IV, which are not exposed to risk from grounding ship, the resulting risk
for loss of life satisfies the annual acceptance criterion
For element V, mainly exposed to risk from grounding ships, the annual accident frequency
estimated with preliminary considerations exceeds the annual acceptance criterion. A specific
protective structure is likely required to mitigate the risk. In order to establish a reasonable de-
sign load for the protective structure, it is recommended to carry out a more detailed risk anal-
ysis for grounding ships.
Flooded tunnel
The case of a flooded tunnel has been analysed by using the longitudinal model 1, see Section 7.4.7.
7.4.1 Introduction
The longitudinal analysis and structural verification are based on the results presented in the following
reports:
1. Longitudinal indicative analyses including appendices, refer [9]
2. Longitudinal indicative analyses – Beam Model, refer [11]
7.4.2 Structural system
The tunnel is designed as a monolithic structure resting on various types of subgrade and fill and car-
rying various types of back fill, erosion protection and sedimentation loads. At the northern portal
building the tunnel is resting on reinforced elastomeric bearings. Due to the monolithic composition of
the structure the temperature deformations are accumulated at the tunnel ends.
7.4.3 FE-models
The following models have been used for the analyses of the structural behaviour in the longitudinal
direction.
1. Model 1: 2-D “shell” model using FEM software LUSAS where both settlements, temperature
effects and prestressing have been analysed. Parts of the settlements are applied as im-
posed settlements.
2. Model 2: 3-D shell model using FEM software LUSAS where settlements and prestressing,
but not temperature effects, have been analysed. Parts of the settlements are applied as im-
posed settlements.
3. Model 3: Beam model using FEM software Autodesk Robot Structural Analysis Professional
2019 where settlements and prestressing, but not temperature effects, have been analysed.
In this model the tunnel is resting on soil springs, which are adjusted to fit the actual settle-
ments. The model is used for the validation of the results of model 1 with regard to bending
and shear.
Longitudinal analyses
Figure 7.4-1 Model 1: 2D shell model.
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Geometry
The tunnel has been modelled in full length in all three models. The actual longitudinal profile has
been used for both model 1 and 2, see
Figure 4.1-2.
Sectional properties
In model 1 and 2 parts of the cross-section that are in tension are given a lower E-modulus than parts
of cross-sections in compression. The reason is that the cross-sections are basically cracked. This
causes a significant decrease of the stiffness due to the low amount of longitudinal reinforcement. The
structure is born with cracks due to the construction sequence (early age thermal and shrinkage
cracks). Furthermore, cracks have developed caused by tension as a result the contraction of the tun-
nel during winter time. For model 1 and 2 the following E-modulus have been used:
Compression: E = 17.000 MPa
Tension: E = 5.000 MPa
In model 3 a single value of E-modulus, of either E = 11.000 MPa or 13.700 MPa corresponding to an
average of the compression and tension E-modulus has been adopted for the whole tunnel.
Support conditions
For model 1 and 2 the vertical supports are modelled by soil springs. The spring stiffnesses have been
estimated based on the information provided in the Geotechnical Summary note [5]. The creep of the
underlying sand fill in the northern end has been modelled as imposed settlements. The most suitable
combination of soil spring stiffnesses and imposed settlements in the northern end has been found by
iteration.
For model 3 imposed settlements are not considered. The soil reaction distribution is determined
through an iteration process with the springs stiffnesses and with an assumed area with no support,
only compression in springs are allowed for.
For model 1 the longitudinal soil structure interaction has been modelled by introducing non-linear
shear springs along the bottom, roof and the outer walls in order - the soil is resisting longitudinal de-
formation of the tunnel, thereby building up axial tension (or compression). The shear stiffnesses are
calculated based on the shear capacities of the soil at the actual location and depth of the element in
question. A linear elastic - perfect plastic shape of the shear resistance diagram as a function of the
deformation has been assumed. The best fit to the actual measurement of temperature deformations
and deformations from the prestressing at the tunnel ends corresponds to a max shear deformation of
20mm in the elastic range.
Furthermore, the best fit to the measured longitudinal deformations is found by assuming no interac-
tion between the shear resistance against the prestressing deformations and against the temperature
deformations respectively, which corresponds to full regeneration of the shear resistance of the soil
after prestressing (that happened only once) before applying the temperature actions that repeats
every year.
Loads
Following loads are considered:
Self-weight of tunnel, ballast concrete, road surfacing and protective concrete
Fill, erosion protection, sedimentation loads
Vertical soil friction on sides (hanging soil)
Settlement
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Water pressure / buoyancy
Prestressing (according to design and drawings; corrected for the presence of the ballast
concrete)
Temperature action – only model 1: Contraction corresponding to max. temperature range
between summer and winter of ΔT = 14
o
C
Results, sectional forces and stresses
Model 1, 2-D shell model
The calculations show that the northernmost part of the tunnel is spanning freely from the bearings at
the northern portal building and approximately 70m further south (tunnel element V).
Concrete stresses in the top and bottom slab for the base model (year 2017) are shown in
Figure
7.4-2.
The peak stresses for tunnel element IV and V clearly reflect the significant sagging and hogging mo-
ments caused by the settlements. The discontinuous curve for the bottom slab reflects the locations
where the post-tensioning forces are applied (anchorage points).
7.4.4
Figure 7.4-2 Model 1, Base model (year 2017). Concrete stresses in top and bottom slab, upper figure without tempera-
ture, lower figure with temperature. Alignment 0 is located at the southern expansion joint corresponding to the global
alignment 292.805.
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It is also clearly seen how the temperature contribution (contraction) increases the tensile stresses sig-
nificantly and brings the main part of top slab / roof into tension, although post-tensioning has been
installed. This means that post-tensioning is not fully efficient with regards to closing the cracks and
keeping the cross-sections permanently under compression. Hence, the water is still able to penetrate
the existing cracks caused by early age thermal effect / shrinkage and further developed by axial ten-
sion from temperature effects before prestressing was applied. That is why leakages are still seen
every year, although the tensile stresses are generally lower than the tensile strength. In other words,
the cross-sections are not able to satisfy the crack width criteria to ensure a watertight structure (SLS).
Figure 7.4-3 Model 4, Future scenario (year 2069), increased settlements, Stresses in top and bottom slab including
temperature
In
Figure 7.4-3
the similar stresses are shown for the future situation in year 2069 with increased set-
tlements. Obviously, the tensile stresses both in the top slab and the bottom slab are increased, but
the corresponding reinforcement stresses are well below the design yielding strength when applying
safety factors in Ultimate Limit State (ULS). However, with regards to leakages, an increase might be
expected in the future because of an increase of the tensile stresses mainly in tunnel element IV and
V.
The future scenario of differential settlements shown on
Figure 7.4-4
is based on a conservative ex-
trapolation of the current settlements with increase of approx. 60 mm (at point of max) in the next 50
years. An additional 30 mm is added in the verifications, see Section 7.4.6.
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Figure 7.4-4 Model 4, Future scenario (year 2069), increased settlements
Model 2, 3-D model
The analyses carried out by the 3-D model have shown that the deflections of outer walls are approxi-
mately 10mm bigger than the deflections of the central wall for element III, IV and V. It should be
noted that the measurements on site are done to the outer walls.
Further, the 3-D model shows that the distribution of shear forces between the walls at the northern
end is very close to 33% - 33% - 33%, even considering various support conditions transversely. In
the C&N design calculations a 30% - 40% - 30% distribution is assumed.
Model 3, 2-D beam model
In general, good agreement is found between the results of model 1 and model 3, which has been
used to validate the results of model 1. However, the sectional forces and the soil reaction forces and
bearing reaction forces are slightly higher for model 3 for the case where vertical soil friction on sides
(hanging soil) are included. For more details reference is made to [11] and [9].
7.4.5 Sensitivity analyses
Several sensitivity analyses have been performed:
With varying E-modulus of the concrete
With / without vertical soil friction on sides (hanging soil)
Without sedimentation load on top of element V
With various free spanning length 80m, 100m, 120m, 150m
From the sensitivity analysis it is observed that with ‘hanging soil’ will the sagging moment increase by
approx. 10% and the bearing reaction forces by 18%, and that removal of the sedimentation load will
decrease the sagging moment by approx. 15% and the bearing reaction forces by 20%.
For further results, reference is made to the sensitivity analyses reported in [11] and [9].
7.4.6 Capacity verifications
Following capacity verifications have been carried out in the longitudinal direction in ultimate limit
state:
1. Bending moment capacity, sagging and hogging moments
2. Shear capacity, global shear
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3. Shear in constructions joints between casting and filling sections and elements
4. Bearings
5. Piles under northern portal building carrying the bearings.
The utilization ratios have been calculated for both the expected lifetime of the tunnel, i.e. 50 years
from now on (year 2069), which is assumed to correspond to additional settlements of max 60 mm,
and for additional settlements of 60 + 30 =90 mm.
Bending moment capacity
The design bending moment diagrams are shown in
Figure 7.4-5
and
Figure 7.4-6
for both the future
and current state. The difference between the diagrams in the two figures is the first one considers the
post-tensioning on the load effect side only, while the other one considers only the secondary effects
of post-tensioning on load effect side. The most critical of the values from the two figures have been
used for calculating the utilization ratios.
The bending moment capacities have been calculated assuming fully embedded prestressing cables,
which is actually not the case. The cables are only structurally connected to the tunnel in the anchor-
age zones and where the deviators are placed. Therefore, reduced bending capacities corresponding
to the yield strength (f
p0,1k
) have been calculated as well, see
Table 7.4-1.
And the utilization ratios are
determined based on the latter. For more details refence is made to Appendix 3 of Longitudinal indica-
tive analyses [9].
Figure 7.4-5 Bending moment in longitudinal direction, ULS combination values (total PT), current and 2069 state
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Figure 7.4-6 Bending moment in longitudinal direction, ULS combination values (Secondary PT), current and 2069 state
X=55m
(max sagging
moment)
Full capacity of ca-
bles
Limited capacity of
cables
1586 MNm
1463 MNm
(0,85)
X=32m
(sagging moment
junction of cables)
1267 MNm
1198 MNm
(0,79)
X = 150m
(max hogging
moment)
393 MNm
383 MNm
(0,65)
Table 7.4-1 Bending moment capacities and utilization ratios, longitudinal direction (X indicates the distance from the
bearing support at the Northern Portal Building).
It should be noted, that the increase of the settlements will increase the tensile stresses in the roof and
base slab, which may increase the amount of leakages. This depends on the ability of the structure to
form new cracks and redistribute stresses.
Shear capacity, global shear
The utilization ratios for global shear are shown in
Table 7.4-2.
The shear capacities are calculated in
accordance with the compression diagonal method as described in section 6.2.3 in DS/EN 1992-1-1
including DK NA. The utilization ratios shown are calculated based on conservative assumptions (only
half of the vertical reinforcement taken into account is case of inadequate anchorage and asymmetric
position of vertical rebars (outer walls)
Shear in construction joints
The utilization ratios for the shear capacity verifications for construction joints are shown in
Table 7.4-2
The most critical vertical construction joint with regards to shear capacity is the closure joint type 2
connecting tunnel element V and the last part of the tunnel that was constructed together with northern
portal building, see
Figure 7.4-7.
For more details, reference is made to section 6 in Appendix 3 of
Longitudinal indicative analyses [9].
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Cast joint at end of el-
ement V, 0.8 m long
Cast joint between ele-
ment V–Portal area
Bearing’s location
Figure 7.4-7 Geometry of northern end of the tunnel (Closure Joint type 2)
The shear capacities are calculated assuming rough interface, also for the keyed joints because full
key cut-off can be assumed.
In the immersion joints type 1, see
Figure 4.3-8,
between the tunnel elements (immersion joints) addi-
tional tension capacity is provided by welded K35/125. This provides approximately twice the capacity
of the ordinary reinforced sections, which is assumed to be satisfactory to carry the additional “pre-
stressing” force in the Gina gaskets plus the external tension force in the cross section, without taking
into account the positive effect of post-tensioning.
One concern is that all main rebars in the immersion joint type 1 and closure joint type 2 are welded
(butt welds according to the drawings). Because of the risk of poor quality of the welding (poor work-
manship) and reduced ductility of the connections it is important that the sections are not fully utilized.
According to
Table 7.4-2
this is the case.
Bearings
The utilization ratios for the bearings are shown in
Table 7.4-2.
The design capacity of the elastomeric
bearings corresponds approximately to the max design reaction forces for bearings in the future sce-
nario, utilization ratio 1,03 assuming a distribution between the walls of 33% - 33% - 33%. Bearings
under the outer walls are the critical ones, because only two bearings are placed here compared to
three under the central wall. The critical verification is yielding in the steel plates reinforcing the rubber
bearings. An increase of the future expected settlements of 50% will increase the utilization ratio to
1,07, compared to a safety factor for the steel of 1,10 and a safety factor of 1,1 x 1,25 = 1,38 for most
of the load effects.
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It is assumed that steel quality St.50-2 or better has been used, which is a rather ductile quality with
high breaking strength (470 MPa) and a high value of elongation at rupture. Therefore, clear signs of
overstress of the bearings are expected in case of overload – expansion of the middle part, possibly in
all directions and cracks in the rubber. It should be noted that the existing bearings can be inspected
and replaced if necessary.
Piles
The axial design capacity of piles is calculated to 1950 KN refer Geotechnical Summary Note [5] com-
pared to a required capacity of approximately 1602 kN, which provides a reserve of around 20%, see
Table 7.4-2.
As the bearing blocks will be sheared following a longitudinal displacement of tunnel ele-
ment V, longitudinal loads may be transferred from the tunnel to the northern portal structure. Assum-
ing a shear stiffness of 5,5 kN/mm for each of the seven bearing blocks and assuming a maximum lon-
gitudinal displacement of 70 mm, the longitudinal load on the pile heads below the portal structure will
not exceed 2,5 MN or corresponding to approximately 40 kN/pile (62 piles). In a medium dense to
dense sand this lateral load should be well within the allowable pile capacity, cf. [5].
7.4.7 Flooded tunnel
The accidental load case “Flooded tunnel” has been roughly analysed, and the utilization ratios are
shown in
Table 7.4-2.
It seems that the tunnel is almost able to resist the increased sectional forces
with reduced partial safety factors
ϒ
= 1,0 except for the reaction forces on the bearings. The load
case will most probably cause increased deformations/settlements that are irreversible due to the sub-
stantial increase of the reaction forces on the soil bedding. Further, cracked areas may need repair
and bearings may need replacement.
7.4.8 Summary of utilization ratios, longitudinal direction
In
Table 7.4-2
The utilization ratios are summarized. Safety factors are applied on both loads and ca-
pacities for Ultimate Limit State (ULS), while all safety factors are equal to 1,0 for Accidental Limit
State (ALS)
Utilization ratios
Future scenario,
2019 + 50 years:
60 mm, ULS
0,85
0,65
0,79
0,71
1,03
0,82
Future scenario + extra
settlements 30 mm:
90 mm, ULS
0,93
0,78
0,84
0,79
1,07
0,85
Flooding, ALS (acci-
dental load case)
~ 1,0
< 1,0
~ 1,0
< 1,0
1,33
< 1,0
Bending moment,
sagging
Bending moment,
hogging
Shear, global
Shear, construction
joints
Bearings
Piles
Table 7.4-2 Utilization ratios, capacity verifications longitudinal direction
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The exceedance for the bearings in ULS is not considered critical. In ALS the exceedance means that
the steel plates in the bearings will yield, but not break (breaking strength approx. 60% higher than
yield strength). However, the bearings will be damaged and shall be replaced afterwards.
Transverse analyses
7.5.1 Introduction
In the transverse direction several analyses have been carried out as described in the following re-
ports:
1.
2.
3.
4.
Analyses of transverse Properties, refer [12]
Assessment of transverse design of Limfjord tunnel, refer [13]
Non-Linear FEM Analysis, refer.[14]
Shear Capacity of Casting Joints in top slab, refer [15] &.[16]
In the first report, the sectional forces in the tunnel are calculated based on a 2D frame model for dif-
ferent support conditions, i.e. different variations in bedding stiffnesses in transverse direction.
In the second report the capacities of the cross-sections are verified both in serviceability limit state
(SLS) with regards to crack width check and ultimate limit state (ULS) with regards to bending and
shear capacity.
In the third report, the load carrying capacity of the tunnel is verified by means of an advanced non-
linear FE model using the FEM software DIANA, since the verifications using the Eurocode in the sec-
ond report indicated that shear requirements (especially in the roof slab) could not be met.
In the fourth report the shear capacity of horizontal interfaces between the original structural concrete
and the repair concrete layer substituting the deteriorated parts has been verified for the roof.
The analyses are described more in details below.
7.5.2 Analyses of transverse Properties
The frame model is made using the software SCIA Engineer (2D plane frame, linear elastic).
The sections in transverse direction have been verified for different types of tunnel sections with differ-
ent reinforcement layouts along the tunnel. The location of the different types of cross-sections (A, B
and C) and corresponding reinforcement layouts (A3, A2, A1, B1, B2; C1) are shown on
Figure 7.5-1.
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Figure 7.5-1 Locations of cross-sections and types of reinforcement arrangements
Geometry and sectional properties
The geometry is accordance with the as-built drawings. The reference model corresponds to cross-
section B, see
Figure 7.5-2.
Figure 7.5-2 Dimensions of cross-section, type B
The concrete properties have been assumed to correspond to C20/25. Outer walls, roof and floor
slabs are modelled as cracked concrete using a reduced stiffness of 1/3 of the original stiffness. The
central wall is modelled as uncracked.
Support conditions
Spring supports are used for the bedding. In the base case of the reference model a uniform spring
stiffness of 2 MN/m
2
has been used, although over the length of the tunnel there is a variation in the
spring stiffness. However, the sensitivity of the tunnel cross section regarding the variation as ob-
served along the tunnel action is very limited. Variation of the spring stiffness in transvers direction has
a larger effect
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The influence on the sectional forces depending on the variation in support conditions in transverse
direction have been analysed by, amongst other means by looking at following cases:
Reduced bedding stiffness K= 50% of the outer parts (1/4 of the width), stiffness K=100% in
the middle part (1/2 of the width). Various values of K have been considered: 1, 2 and 5
MN/m
2
.
Reduced bedding stiffness K= 100%, 50%, 10% and 0 % on the outer 3m in both sides.
The above cases are considered to give the range of likely stresses in the tunnel cross section.
Results
For the most critical part, the roof, the influence of the variation of the bedding stiffness is not signifi-
cant.
The shear and bending moment diagrams for ultimate limit state, ULS, are shown for the most critical
section (293060) in
Figure 7.5-3.
The location of the section is shown on
Figure 7.5-1.
Figure 7.5-3 Shear force and bending moment diagrams, ULS, section 293060
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7.5.3 Capacity verification
Checks have been carried out comparing the capacities with the sectional forces calculated by the
SCIA-model, described above. Only permanent loads (self-weight, hydraulic and ground loads, dead
loads) have been considered, representing most of the loads (>95%). For potential additional load ef-
fects, 10% has been added to the sectional forces, which is considered conservative.
All capacities are calculated in accordance with DS/EN 1992-1-1 including DK NA.
Properties
Following material strengths, E-modulus and partial safety factors are used in the verifications:
Concrete compressive strength: f
ck
= 25 MPa
Partial safety factor, compressive strength and modulus of elasticity: ϒ
C
= 1,45
Partial safety factor, tensile strength of concrete: ϒ
C
= 1,70
Yielding strength of reinforcement: 410 MPa
Partial safety factor reinforcement: ϒ
S
= 1,20
E-modulus: 6.000 MPa
Results
The results are shown in
Figure 7.5-4.
Section
Bending moment, ULS
Roof
293010
293060
293200
293250
293250 3p
293350
293350
sed
0,78
0,87
0,88
0,74
0,64
0,41
0,63
Wall
0,53
0,51
0,58
0,48
0,45
0,28
0,42
Floor
0,98
0,99
0,90
0,76
0,84
0,73
0,76
Crack width, SLS
Roof
0,55
0,81
0,86
0,65
0,51
0,32
0,51
Wall
0,32
0,31
0,34
0,26
0,28
0,19
0,24
Floor
1,01
1,07
0,90
0,66
0,80
0,64
0,66
Shear, ULS
Roof
0,77
1,66
1,63
1,35
1,24
0,86
1,13
Wall
0,48
0,46
0,41
0,35
0,50
0,29
0,29
Floor
0,65
1,09
0,79
0,84
0,65
0,62
0,57
Figure 7.5-4 Utilization ratios crack width, bending moment and shear capacity verification, transverse direction, Loca-
tion of the Sections, refer Figure 7.5-1
For crack width control in SLS, the max allowable crack width is 0,20mm corresponding to expo-
sure/environmental class EA (extra aggressive). It is seen from the figure that the crack width limit is
fulfilled for almost all cross-sections and only slightly exceeded in few sections.
While the bending moment capacities in ULS are satisfactory for all cross-sections, the shear capaci-
ties are exceeded with the highest utilization ratios in a section with distance approximately 1,7m from
the face of the central wall, where the bent-up rebars are stopped. The arching action for the non-
shear reinforced sections closest to the support has been considered in accordance with the rules in
the Danish national annex DK NA to DS/EN 1992-1-1.
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7.5.4 Non-linear analyses by FEM software
Due to the significant exceedance of the shear capacities it was decided to calculate the ultimate car-
rying capacity of the tunnel section by means of more realistic and more advanced non-linear elastic
analyses using the FEM (Finite Element Model) software DIANA and carry out the verification accord-
ing to the State of the Art FIB ModelCode 2010.
Figure 7.5-5 Modelling every single rebar and applied FE Mesh
The FEM software package DIANA (DIsplacement ANAlyzer) is able to simulate the structural, physi-
cal non-linear behaviour of the reinforced concrete structure. In the nonlinear analysis the total load
combination (ULS) is applied using a force-controlled application of loads. This means that the total
load is applied incrementally with small steps of about 1% from the moment that the structure starts to
behave non-linear, so when the first cracks are initiated. Increasing the load until the structural col-
lapse will determine the capacity in terms of a Load Factor over the total load combination. The Load
Factor defines failure of the structure (above the ULS mean load factor of 1,38) as well as the safety
level that is present in the structure.
Figure 7.5-6 Load factor displacement diagram
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Assumptions
The partial safety factor method has been used, which means that safety factors have been applied to
both loads and material strengths. For the Base Case the material strengths and partial safety factors
listed in Section 7.5.3.1 have been used. These material properties comply with the original design
starting points.
The fracture energy defined in FIB Model Code for Concrete Structures 2010 has been used and
transferred into a characteristic value, which has been applied the same safety factor as for the con-
crete compression strength.
The capacity is calculated for section 293.060 and considering the Ultimate Limit State (ULS load fac-
tor 1,1×1,25 = 1,38 included).
It is assumed that the sections are intact, i.e. full interaction between original and repair concrete is
assumed (also see Section 7.5.5, that confirms that this assumption is justified).
Results
The analyses have been carried out after the material models have been validated based upon back
analysis of real experiments and after sufficient testing the FE model for the tunnel cross section. For
the Base Case the load factor is calculated to 1,35. This is in fact additional to the Ultimate Limit State
and actually represents a “safety level” of 1,38 × 1,35 = 1,86. The corresponding crack patterns and
deformation plot are shown in
Figure 7.5-7.
Figure 7.5-7 Base case. Crack patterns at max load level
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It is seen that the critical section is close to the outer wall, where the haunched section and bent-up
rebars start, and not as expected from the previous calculations the non-shear reinforced sections
closest to the central wall. It should be noted though, that the crack patterns indicate that this section
is close to be critical as well.
Several additional analyses have been undertaken to examine the sensitivity of the structure to the as-
sumptions. The analyses are indicated in the table below including the achieved Load Factors and
“Safety” Levels.
CASE 
Load Factor 
"Safet "  
E planation 
Base Case
Impact of reinforcement variation (re-
duction)
Effect of higher concrete strength
(compliant with actual and recent lab
test results)
Impact variation Fracture Energy
1,35
1,24-1,09
1,60
1,86
1,71 / 1,50
2,21
30% reduction, removing 1-3 bent-up rebars
Concrete strength 40N/mm2
1,10-1,54
1,52 - 2,13
Parameter that describes the performance of structure
during development of cracks (0,5 * and 2,0 * the most
likely value)
50% reduction of axial force in roof slab
Bedding 50% over 3m from outer wall / 200% over
outer half of the cross section
Impact reduction of relieving forces
Impact of foundation support
1,35
1,42 / 1,45
1,86
1,96 / 2,00
Figure 7.5-8 Sensitivity analyses and results.
From the table it can be concluded that the effect of an increased concrete strength f
ck
= 40 MPa is
quite substantial with a Load Factor of 1,60. Considering the results of the condition assessment (Sec-
tion 6.2) it is concluded that considering this increased concrete strength is reasonable and in fact pro-
vides a better prediction of the actual safety of the structure.
Several other cases e.g. considering a reduction of the reinforcement has been considered. These
analyses identify robustness for any future corrosion scenarios. From the results it can be concluded
that the structure under very adverse assumptions still performs with Load Factors from 1,09 to 1,24.
Due to the fact that with the Non-Linear Elastic Analyses the structure is modelled in a more realistic
way, there is “less hidden” spare capacity than in a simpler Linear Elastic model. For that reason, a
higher “safety level” between 1,8 – 2,0 would be appropriate (Load Factor 1,3-1,4) for the Base Case
and the case considering the increased concrete strength. Obviously, for other analyses considering a
(significant) reduction of rebar or exploring an extreme bandwidth of parameters (such as in Fracture
Energy variation) much lower safety levels are acceptable.
With the advanced Non-Linear analyses and verifications following a more State of the Art Design
Code (Model Code 2010) it could be demonstrated that the structure still meets the various design re-
quirements. The various additional analyses have shown that the structure can handle variations in
critical parameters very well. The study and the results have been reviewed by an expert of the Tech-
nical University of Copenhagen.
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7.5.5 Assessment of interface between original and repair concrete of the roof
In 1998 comprehensive concrete repairs were carried out in The Limfjord Tunnel. Chloride infected ar-
eas in the tunnel ceiling and the walls were removed by water jetting. Corroded reinforcement was re-
placed, and new concrete was cast to replace the removed concrete. In case of any voids, these were
injected.
During inspections carried out in 2007, indications of delaminations and water pockets were found in
the repaired areas especially in the tunnel ceiling.
In case of significant delamination of a large area the repair concrete and reinforcement may not con-
tribute to the bearing capacity as anticipated. Approximately 32.500 anchors were therefore installed
in 2010 - 2012 in the ceiling to secure the connection between the original concrete and repaired con-
crete. This due to the fact that calculations showed that the load bearing capacity was insufficient, if
more than 71 mm of concrete was disregarded. It is therefore vital that the anchors are functioning as
assumed.
The shear capacities of the horizontal interfaces between the original concrete and the repair concrete
have been verified using two slightly different methods:
1. Section 6.2.5 in DS/EN 1992-1-1 including DK NA (Eurocode)
2. Section 6.3.4 in fib Model Code 2010
The main difference between the two methods is that the method in the Model Code includes a certain
contribution from dowel action, which is more realistic and may be relevant for the sections of the tun-
nel roof, where anchors have been installed.
Where anchors are not installed, the capacity solely depends on the cohesion contribution. In this
case the cohesion coefficient, c, should be conservatively estimated.
The investigations were carried out according to the number of anchors that were originally designed
to be installed (in the following called "designed anchors") and the number of anchors that were actu-
ally installed (in the following called "installed anchors"). The actual number of anchors installed in tun-
nel element V cannot be found. Therefore, the investigations for element V is only based on the de-
signed anchors for this tunnel element.
Shear capacity according to section 6.2.5 in DS/EN 1992-1-1 including DK NA
The shear capacity is in general insufficient when only the anchors are considered to contribute to the
shear capacity. Overutilization up to 3,06 have been identified.
Therefore, calculations have been carried out to estimate the needed contribution from cohesion to
obtain a utilization that is less than 1,0. For the majority of the areas a contribution of 25% of the theo-
retical cohesion is sufficient to fulfill a sufficient shear capacity, whereas for a few zones a contribution
of 50% is needed from cohesion.
An example of calculated utilization ratios in element III according to installed anchors are shown in
Figure 7.5-9
and the additional capacity needed from cohesion when 25 % cohesion is taken into ac-
count are shown in
Figure 7.5-10.
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Figure 7.5-9. Installed anchors - Utilization for Element III, west and east tunnel. Red areas indicate utilization higher
than 1,0.
Figure 7.5-10. Element III installed anchors and 25% of the theoretical cohesion is taken into account. The numbers
indicate the additional capacity needed from cohesion to fulfil a utilization of 1,0.
It must be noted that if a zone is overutilized, it does not necessarily apply to the whole area within the
zone but only to the most critical area within the zone.
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Shear capacity according to section 6.3.4 in FIB Model Code 2010
The results from the alternative calculation method in accordance with section 6.3.4 of Model Code
2010 show in general satisfactory capacities also for the case with only 50% contribution from the con-
crete
An example of calculated utility ratios in element III are shown in
Figure 7.5-11.
Figure 7.5-11. Installed anchors – Fib model code - Utilization for Element III with 50% contribution from the concrete.
The low utilizations from the fib model code compared to the Eurocode approach stems from the fact
that interlocking between the interface of concrete cast at different times (which it is considered to be
the case for the Limfjord Tunnel) has been included in the load bearing capacity and added to the load
bearing capacity from anchors including dowel effect.
Interface/cohesion assessment
From concrete cores taken out during the condition assessment on site it is found that in limited areas
the interface might be delaminated. On the other hand, the interface can be considered as rough be-
cause the interface is evidently rather uneven. If no delamination was seen the required capacity
would be met in all areas.
From the condition assessment carried out as part of this project, it is found that at least 50% cohesion
is available in the cores, indicating that the load bearing capacity in the construction joint is sufficient,
cf.
Table 6.3-1.
Condition assessment
To secure that the shear capacity will be fulfilled in the years to come, regular inspections must be car-
ried out.
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Further, areas without anchors must be inspected for delamination on a regular basis. If delamination
is developed in these areas, anchors must be installed.
The results of the structural analyses with regards to the structural safety can be summarized as fol-
lows.
7.6.1 Longitudinal direction
It has been verified that the tunnel has adequate resistance with satisfactory margins to carry the in-
creased loads because of the on-going settlements and to cover the uncertainties related to the esti-
mates. However, an increase in the tensile stresses might be expected in the future because of the
on-going settlements leading to more leakages.
7.6.2 Transverse direction
It has been verified that the tunnel has adequate resistance to carry the loads in transverse direction
with satisfactory margins taking into account the uncertainties related to the input to the advanced
non-linear FE model and to the repaired parts of the roof where both concrete and reinforcement have
been replaced.
Conclusions
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8 Basic Maintenance and Repair
Strategy
The Basic Maintenance and Repair Strategy is basically a "business as usual" -strategy supplemented
by a number of additional activities recommended by the Expert Group. Only one strategy is consid-
ered, but this strategy comprises a number of recommended activities. This Section 8 of the Technical
Summary Report is based on [18].
The Basic Maintenance and Repair Strategy for the Limfjord Tunnel contains recommendations for the
coming 50 years concerning major maintenance, repairs and refurbishment. The recommended activi-
ties are to be seen as supplementary to the standard O&M-activities continuously going on in the tun-
nel. The recommendations in this section are based on input from inspections undertaken in 2018-
2019 and input from the Structural Expert Group.
The basis for the standard O&M activities are the activities that are identified in the 10-year plan for
the Limfjord Tunnel as is the case for all other major tunnels and bridges administrated by the Danish
Road Directorate.
The Basic Maintenance and Repair Strategy (BMRS) is quite complex for the following main reasons:
The BMRS is a continuous strategy that must be planned for the following 50 years.
It may be difficult – especially for the repair activities – to foresee when they will need to be
implemented – as it is difficult in details to foresee how the condition of the different parts of
the tunnel will develop.
The BMRS – in combination with the basic O&M-activities – contains several activities that are
interrelated and influence each other.
The goals of the BMRS are the following:
1. First priority: Maintain the current condition
2. Second priority: Decrease (cause of) deterioration
3. Third priority: Monitor rate of/change in deterioration.
The activities in the BMRS are divided into four main groups under the following headings:
Inspection and monitoring
Preventive maintenance
Repair and refurbishment
Recommendations from the Structural Expert Group
Introduction
The structural assessments carried out by the Structural Expert Group has resulted in a number of
recommended activities to be part of the Basic Maintenance and Repair Strategy. The recommended
activities include:
Actions recommended
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Measurement of settlements and movements of the tunnel by for example fibre optics. This
will give a reliable warning related to an increased rate of settlements and possible develop-
ment of localized axial movements in e.g. a casting joint which could indicate yielding rein-
forcement
Measurement of the bearing load at the northern portal building by temporary jacks for in-
stance every 15
th
year. This will give a confirmation of some of the key assumptions related to
the structural analysis and assessment in the longitudinal direction, e.g. free spanning length
of tunnel element V and loads from backfill and sedimentation.
Detailed investigation of grounding ship load and tunnel capacity. This could involve a more
detailed risk analysis compared to the risk analysis carried out in [17] and the outcome of this
analysis could be that protective measures will be required to protect tunnel element V
Detailed evaluation of the risk of a flooded tunnel due to water entering one of the tunnel
ramps. The outcome could be that flood protection measures will be required around the tun-
nel portal and ramps.
Detailed analysis of the need for repair or renewal of fire protection. During the inspections
carried out in the Limfjord Tunnel it has been observed that the fire protection is deteriorating
in certain areas of the tunnel. Further, it is found that this deterioration of the fire protection is
related to and adversely affected by water ingress.
Detailed evaluation on the implication of removing sedimentation on top of tunnel element V
inclusive environmental issues and likely unit weight of future sedimentation material.
Establish a detailed survey of injection material being injected into the tunnel elements during
the period where detailed records from the injection campaigns exit. The survey should if pos-
sible include date, location and amount of material. (Historical data)
It is recommended that grout volumes used during the crack injection campaigns are logged
systematically. It is also recommended that grout volumes can be linked to selected tunnel
sections to follow trends in the future. (Future data.)
The activities above will supplement the more basic monitoring and inspection activities traditionally
carried out in the Limfjord Tunnel.
The proposed activities included in the Inspection and Monitoring program are summarized in
Table
8.3-1.
The proposed program is quite comprehensive and includes both inspections that are to be consid-
ered as standard (such as IM01, IM 02, IM06 and IM07) for a tunnel structure and measurements that
are considered rather special such as IM10.
Further the proposal involves installation of equipment for continuous monitoring of corrosion of the
reinforcement and the moisture content in the concrete structures (IM05).
Inspection and monitoring
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ID
IM01
Issue/Method
Settlements – manually or by
means of optical fibre (when in-
stalled)
Frequency
Yearly / continuously
Extent
Whole tunnel (as today)
IM02
Movements at tunnel ends (man- Yearly
ual measurements)
Logging of extent of crack injec-
tion
Yearly
Both ends (as today)
IM03
During yearly injection campaign
IM04
Inspection of critical wall sections Yearly
at immersion joints and closure
joint
Immersion joints and closure joint in
both tubes – walls only
(Visual inspection + crack width meas-
urements where relevant)
TE III (4 – 6 places)
IM05
Permanently installed monitoring
of corrosion and moisture
HCP
1)
+ break outs
Continuously
IM06
Every 6 years
Selected areas in TE III, IV and V.
Spot check in TE I and TE II.
(Special attention on transition zones
between wet and dry areas.)
Selected areas in TE III, IV and V
based on HCP measurements.
Spot check in TE I and TE II.
Selected areas in TE III, IV and V
based on HCP measurements and other
observations.
Spot check in TE I and TE II.
Monitor signs of yielding of steel plates
on all bearings (Northern end).
All bearings (Northern end)
(First time within the coming 1-3
years)
3 – 5 places distributed over the bot-
tom part
IM07
Chloride profiles
Every 6 years
IM07
Cores for macro analysis and thin Every 9 years
sections (analysis should include
level of ASR
2)
)
IM08
Visual inspection of bearings +
measure geometry of bearings
Determine load on bearings by
means of jacks
Yearly
IM09
Every 15 years
IM10
Visual inspection of the southern
movement joint using endoscope
through cored inspection holes
Every 3 years
Table 8.3-1 Proposed inspection and monitoring program for the Limfjord Tunnel. TE x = tunnel element I to V.
1)
HCP (= half-cell potential) is an (almost) non-destructive test method that is used to assess the risk of corrosion of
ASR = Alkali Silica Reactions.
reinforcement.
2)
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The major preventive maintenance and repair activities foreseen for the structures are the following:
.
Crack injection
Crack injection is a preventive maintenance activity that has been going on for a number of years al-
ready. The injections are carried out once a year – usually in December. The work is carried out in the
night time during an ordinary tunnel closure. The main purpose of the injection scheme is to stop ac-
tive leakages. The work is quite effective over a longer period of time, which means the injection only
has to be carried out once a year.
It is recommended by the Structural Expert Group that crack injection continues once a year as long
as there is a need. Further, it is recommended that the amount of crack injection is registered for every
injection campaign in order to follow the overall development in the injections needed to keep water
ingress at an acceptable level.
Cathodic protection
Cathodic protection is a standard method to stop the development of corrosion of reinforcement. In
Denmark this measure has been installed during the past 10 years on a number of the main bridges
and tunnels administrated by the Danish Road Directorate.
So far cathodic protection (CP) is not used in the tunnel part of the Limfjord tunnels but it was installed
in some areas of the ramp walls some years ago.
As the Limfjord Tunnel is found to have an increased risk of corrosion due the water ingress in the tun-
nel structures it is foreseen that installation of CP may become relevant within the coming 10 to 20
years. In comparison to traditional concrete repairs the installation of CP has several advantages:
CP can be installed and put into service before corrosion has caused damage to the concrete.
CP is quite easy to install in a tunnel where all structures are readily accessible from the in-
side.
CP can be installed during standard night closures. Hence, the impact on traffic is quite lim-
ited. However, in practice, for a smooth and efficient installation, either the south or north go-
ing tube must be closed for installation.
The main downside of installing CP is that it requires constant monitoring (this can be done almost
fully automatically however) and that the electrical parts of CP needs replacement approximately
every 15-20 years.
Preventive maintenance and repair
In order to know when follow up is needed on the monitoring activities, trigger values have been de-
fined for a number of key parameters included in the monitoring activities.
The background for the trigger values are described in Section 8.5.1 trough Section 8.5.3. In Section
8.5.4 an overview of all the trigger values is given.
8.5.1 Total settlements
In general, satisfactory spare capacities in the ultimate limit state (structural safety) are found for all
verifications in the longitudinal and transverse directions.
Trigger values
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The increase in sectional forces in the longitudinal direction is caused by the settlements. However, in
case of bigger future settlements than expected the increase is moderate. An increase in settlement of
approximately 50% (+30mm) in addition to the predicted future settlements from 2017 to 2069 of
60mm is still within the acceptable limits of the ULS structural capacity in the longitudinal directions.
Since the post-tensioning cannot be considered as internal fully embedded an extra safety margin
should be considered. This extra safety margin is covered by the structural assessment in Section 7.4,
where the above-mentioned increase in settlement of 30mm has been taken into account.
The link between the total settlements and the ULS capacity along the tunnel alignment can then be
expressed through the following guidelines:
Green area on
Figure 8.5-1:
ULS capacity is OK
Yellow area: The ULS capacity of the tunnel structure is OK but the vertical load on the bear-
ing blocks shall be measured and the longitudinal analyses shall be updated ensuring compat-
ibility between total displacements and the load on the bearing block.
Below yellow area: The ULS capacity of the tunnel structure does not comply with existing
regulations.
Figure 8.5-1 Settlements of tunnel structure since 1969. Colour-code relates to whether the tunnel structure complies
with existing regulations considering the ULS capacity.
To be able to adjust and react in time before the total settlement reaches the yellow area in
Figure
8.5-1
it is suggested to include a maximum settlement rate as a trigger value. The settlement rate
could be measured over a period of at least 5 years and it shall be reviewed if it exceeds 3 mm/year.
8.5.2 Differential settlements
Limits for differential settlements are included through the maximum allowable inclination of a tunnel
section relative to horizontal. A tunnel section may not be inclined more than the “as-installed” inclina-
tion from 1969 plus 2.5 mm/m (average value along 10 m), and if the value is exceeded, longitudinal
analyses shall be initiated to clarify the consequence. The value of 2.5 mm/m corresponds to the incli-
nation of the lower boundary curve of the yellow zone where the red cross is shown on
Figure 8.5-1.
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8.5.3 Condition monitoring
A number of key parameters for increased monitoring has been identified. In order to secure timely in-
tervention in case of deterioration of the structural elements of the Limfjord Tunnel a number of trigger
values for these key parameters need to be identified.
This section contains a proposal for key parameters to keep under close observation as well as pro-
posals for trigger values for these parameters where remedial actions should be considered. Also as-
sociated preventive actions are identified.
8.5.4 Key parameters and trigger values - Overview
All the key parameters and the corresponding trigger values are summarized in
Table 8.5-1
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ID
Structural element
Key parameter
Trigger value
Preventive action /
Follow-up
Increased monitoring of corrosion
TV1
Outer walls and roof
(wet areas)
Outer walls and roof
(wet areas)
Outer walls and roof
(dry areas
1)
)
Water content
Degree of saturation < 80
%
Corrosion rate > 10
μA/cm2
> 0,05%
TV2
Corrosion rate
Increased inspections (HCP + break
outs)
Increased focus on signs of corro-
sion
TV3
Chloride content by
concrete weight
> 0,1%
TV4
Outer walls and roof
(dry areas
1)
)
Roof (Areas without
anchors)
Closure joint
(Joint type 2 )
Corrosion rate
Corrosion rate > 10
μA/cm
2
Signs of delamination
Break outs to look for corrosion
Increased inspections (HCP + break
outs)
Install supplementary anchors
TV5
Delaminations
TV6
Cracks
Visible cracks
Monitor development in crack width.
Analyse need for remedial action
(lowering of north end).
TV7
Immersion joints and Corrosion rate
closure joint
(Joint type 1 and 2)
Construction joint
type 2 and type 1
TE III, IV and V
Corrosion
Corrosion rate > 10
μA/cm
2
Increased inspections (HCP + break
outs) – prepare for CP
TV8
> 10 % area loss
Cathodic protection (CP)
TV9
Settlements
> 60 mm (from 2019)
> 3 mm/year
Analyse need for remedial action
(pre-stressing or lowering of north
end)
Analyse need for remedial action
(new bearings)
Renewal of steel parts or new
Omega joint
Follow-up analysis
TV10
Bearings
Increased deformations Signs of yielding of steel
plates
Corrosion of steel parts Significant corrosion
TV11
Southern movement
joint
TV12
Concrete, outside and Expansion on concrete
inside cores
samples due to ASR
2)
TE III to TE V
Extent of crack injec-
tion
Expansion > 0,1%
TV13
Increase year-by-year >
20%
Follow-up analysis
1)
Dry
2)
area = Areas where "Degree of saturation" < 80%
ASR = Alkali silica reactions (Test method: TI-B 51 modified for use on samples from existing structure.)
Table 8.5-1 Key parameters for monitoring with associated trigger values. The stated trigger values need to be re-eval-
uated from time to time based on results from inspections.
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The repair activities described below should be prioritized.
Concrete repairs
Some concrete repairs may be necessary within the next 15 to 25 years.
Closure joints
The main concern is concrete repairs in the closing joint areas as the structural analyses carried out
during the life extension project has shown that the utilization ratios of these areas are quite high.
This, combined with possible future corrosion of the reinforcement, may lead to a need for repairs in
these areas.
The planned close monitoring of these areas, and the possibility of installing CP, if active corrosion is
observed, does however mean that the risk of these repairs becoming necessary is limited. Further-
more, the repairs – if needed – will be limited in extent and size.
Roof
There is a risk that water pressure will build up at the interface between original concrete and repair
concrete as the repair concrete is quite impermeable.
Hence, the implementation of a rather extensive inspection and monitoring scheme is recommended.
This scheme in combination with cathodic protection is assessed to be an effective way to prevent sig-
nificant damages to the roof to develop.
It may be considered to establish a number of weep holes through the repair concrete in order to re-
lieve the water pressure assumed to build up at the interface between repair concrete and the original
structural concrete.
Walls
Due to the constant water pressure a need for repairs may occur on the walls e.g. due to loose tiles or
corrosion.
The implementation of a rather extensive inspection and monitoring scheme in combination with ca-
thodic protection is assessed to be an effective way to prevent significant damages developing.
Hence, only small, local concrete repairs on the walls are foreseen.
Bearings
Repair - or most probably – renewal of the existing bearing at the northern end of the immersed part of
the tunnel, which may become relevant within 10-20 years, is dealt with in one of strategies of the
structural subgroup – see Section 9.3.3.
Movement joints
The Limfjord tunnel has movements joints at both ends. The layout of the joints is quite different in the
two ends.
At the northern movement joint the omega seal, being a vital part of the movement joint, will be re-
placed in 2019.
Expected repair activities until 2069
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The current state of the omega seal in the southern end is currently unknown as it is not readily acces-
sible for inspection. It is recommended that the seal and the adjoining fastening arrangements are
thoroughly inspected within the coming year to determine the condition.
It must be foreseen that it will be necessary to repair or replace the southern movement joint within the
next 25 years. This project will include demolishing the concrete forming the cover of the joint. This
means that this work will have considerable impact on the traffic in the tunnel. Hence, it is preferable
that this work can wait till the third Limfjord link has been established in 2030. As long as the current
condition is not known it is, however, difficult to assess whether this is a realistic scenario.
A number of aspects do, however, make it reasonable to assume this to be a realistic scenario:
The joint is placed on land and is subjected to a rather low water pressure,
only considerable degradation of the joint will cause significant inflow of water,
there is no reason to believe that the Omega-profile will fail within foreseeable time as this
type of profile is known to have a long service life when it is not subjected to overload or
critical deformations (which is assessed not be the case).
It is recommended that the ongoing schedule of standard operation and maintenance is continued. A
number of additional monitoring activities and regular in-depth inspections are also recommended.
An increased level of monitoring is recommended due to the Limfjord Tunnel being a “high risk” struc-
ture. This classification is due to an increased exposure to water ingress and chlorides and the related
risk of corrosion, delaminations and other damages.
Due to big load effects, immersion joints and (in particular) the closure joint shall be inspected yearly
for signs of overload.
The combination of an increased schedule of inspection and monitoring and the possibility of imple-
menting cathodic protection before significant damages have developed means that no major repairs
are expected within the next 10-15 years.
The current state of the movement joint in the southern end of the tunnel needs to be established.
Based on for example, Dutch experience there is a risk that the clamping structure of the Omega seal
will (locally) need replacement or refurbishment within less than 10 years. This may cause significant
disturbance to the traffic as the southern movement joint is placed in a small recess below the road-
way and therefore can be reached only by removing the concrete above the joint (obviously depending
on the area and location that would need repair / replacement).
The overall maintenance plan must take into account the possibility of a third crossing over the Lim-
fjord within 10 years. This gives the opportunity – when the new connection is open and traffic in the
Limfjord Tunnel reduced - to close either north or south running tunnel tube for a longer period in order
to make the necessary repairs or strengthening.
Conclusions
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9 Retrofitting strategies
A number of potential retrofitting strategies – close to 20 -have been identified and evaluated by the
Expert Group.
The strategies can be grouped as follows:
Geotechnical strategies
Structural strategies
The geotechnical and structural strategies were identified to either mitigate the effects of the ongoing
settlements in the northern part of the immersed section (element V) or to mitigate the effects of the
leakages in mainly the middle part of the immersed section (e.g. elements III and IV). The basic
maintenance and repair strategy is focusing on the mitigation of the effects of the leakages in mainly
the middle part of the immersed section.
The considered strategies were assessed using an initial screening process. This adopted a quanti-
tively based assessment of the identified options. One geotechnical retrofitting strategy (settlement
mitigation) and two structural retrofitting strategies (leakage and settlement mitigation) were chosen for
further development based on the above assessment.
The pre-screening process and the selected geotechnical and structural strategies are presented in
further detail in the sections below.
Methodology
9.2.1 Purpose
The main aim of any geotechnical retrofitting solution is to control or reduce the expected ongoing set-
tlement of the tunnel as described in Section 5 to acceptable limits and/or reduce the geotechnical
loading on the tunnel. This would in turn control and reduce the stresses in the tunnel structure. An op-
tioneering process was undertaken to assess feasible geotechnical solutions. This process is de-
scribed in detail in the background document
Geotechnical Retrofitting Options [6]
and is summarised
briefly below.
9.2.2 Optioneering process
The optioneering process initially considered a wide variety of possible geotechnical retrofitting solu-
tions that could potentially be undertaken to improve the performance and life of the structure. The so-
lution options were based on typical industry proven ground engineering techniques which could po-
tentially be used in the conditions at Limfjord.
These initial options were pre-screened, and the subsequent feasible options were then assessed in
order to determine a preferred option which, would then be assessed in more detail. The assessment
of the feasible options considered the performance requirements, constructability, costs and re-
strictions outlined in the report
Geotechnical Retrofitting Options report [6].
Geotechnical strategies
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Feasible options that were considered are outlined below;
1. Soil improvement using vertical jet grouting;
Option 1:
Adjacent to the tunnel installed from a jack up rig.
Option 2:
Partially under the outer walls installed from a jack up rig.
Option 3:
Beneath the tunnel installed from within the tunnel during lane closures.
2. Horizontal grouting installed under the tunnel from cofferdams adjacent to tunnel.
Option 4:
Active compensation grouting inducing a positive lift to the tunnel.
Option 5:
Horizontal volume grouting providing soil improvement (Passive)
3. Unloading
Option 6:
Replacing Sand Fill adjacent to the tunnel with lightweight aggregate.
Option 7:
Removing soil overburden on element V by dredging.
Based on the optioneering process undertaken the highest scoring solution is option 7, removing the
overburden from element V. However, this option has a very low technical score due to the negligible
reduction of the settlement and would only be appropriate if the removal of the loading provided the
required benefit to the tunnel structure. The total cost for the removing the overburden from element V
is expected to be less than €1m.
The next highest scoring option is option 4, the active compensation grouting solution. Although this is
one of the more expensive feasible solutions it provides the highest technical performance. This pre-
ferred option is the only one considered that could provide a positive temporary lift to the structure re-
ducing the long-term settlement and mitigating the risk of any settlement caused by the installation
process. The proposed solution is fully detailed in the geotechnical retrofitting report [7] and is summa-
rised in Section 9.2.3 below.
The likely performance in terms of settlement reduction for many of the other options was considered
not to have sufficient benefit for the structure when related to the cost of installation and other risks
and issues considered.
9.2.3 Preferred Geotechnical Option: Active horizontal compensation grouting
Compensation grouting is a geotechnical process that is used to control the settlement of structures
and can be used to also lift the structure from its present position.
The method involves the injection of
grout into the ground immediately below the structure which results in an expansion of the soil. This
can counteract any settlement that has occurred and can provide a controlled uplift of the tunnel struc-
ture to compensate for the predicted future ground settlement (approximately 60mm to 2069).
For the Limfjord tunnel the injection of the grout and control of any induced heave can be carried out
from cofferdams located outside of the tunnel structure and hence there would be no significant dis-
ruption to the tunnel users.
To provide a positive heave of the tunnel, precondition grouting of the
Sand Fill will be required below the main compensation grouting area and two rows of horizontal bore-
holes at separate levels may therefore be required.
Control of the grouting can be very selective inducing very small level changes of varying amounts to
reduce the risk of inducing further stress in the tunnel structure. The compensation grouting treatment
would be installed from the midpoint of element IV to approximately 25m from the Northern Portal (i.e.
125m long over the full width over the tunnel)
as shown in
Figure 9.2-1 and Figure 9.2-2.
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The basic sequence to undertake the compensation grouting process for Limfjord would involve the
following;
1. Installation of a bespoke monitoring system in the tunnel to provide real time structure move-
ment information.
2. Construction of marine sheet pile cofferdams at a suitable distance from the tunnel enabling a
drilling and grouting working platform at the required depth approximately 4m below the base
of the tunnel. Two cofferdams would be required. A Jet grouted or a concrete base plug and
tension piles are likely to be required below the base to resist high water pressures and pro-
vide base stability.
3. Installing ship impact protection piles to provide protection to the cofferdams during the grout-
ing process. See
Figure 9.2-1
4.
Installing two levels of horizontal grout injection tubes to a pre-determined pattern under the
structure. See
Figure 9.2-2
and
Figure 9.2-3
.
The drilling techniques to be adopted will ad-
dress the high water pressures and poor ground conditions that will be present at this level.
5. Injection of pre-treatment and main compensation grout through the grout injection tubes with
careful process control to induce required tunnel uplift movements.
6. The tunnel would be monitored for all stages of construction from the installation of the cais-
sons and during the installation of the injection tubes and grouting process.
Figure 9.2-1 Indicative plan showing cofferdams and ship protection piles.
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Figure 9.2-2 Plan showing indicative layout of grout injection tubes.
Figure 9.2-3 Section showing indicative pre-treatment and compensation grout injection tubes.
The construction programme is expected to be in the order in the order of 17 months.
Information on the project risks and mitigation measures are also provide in the detailed report [7].
The actual effects on the tunnel structure using this option will need to be analysed and assessed dur-
ing the detailed design phase but it is expected that the lifetime of the structure will be extended by the
option proposed.
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9.3.1 Purpose
The structural retrofitting strategies – pre-screening of options - identified 7 numbers of feasible op-
tions. Three options were regarding remedial works dealing with defects only related to the structural
safety. Investigations have concluded that they are not relevant/necessary. The remaining four options
were regarding remedial works dealing with limiting the crack width or close the cracks (tensile
stresses) to reduce future leakages, improve durability and limit the extent of the injection campaigns.
The pre-screening of options included a comparison of the feasible relevant options. The scoring sys-
tem used in this comparison resulted in a ranking of the options where additional prestressing became
number 1 and replace bearing blocks became number 2.
9.3.2 Additional prestressing
In 1993 – 1994 post tensioning cables were installed in the ballast concrete. A total of 30 cables type
Freyssinet 12L15 were embedded in each tunnel tube and the total tension force for the tunnel cross
section (at 80 % tension) was 150 MN. The positive effect of this tensioning project has been docu-
mented. It has been argued that further tensioning would have been beneficial – up to twice the in-
stalled capacity has been mentioned. The additional post tensioning can reduce the tensile stresses
and cracking from both seasonal temperature variations and future settlements and thereby increase
the durability of the tunnel and reduce the extent of the injection campaigns.
It was chosen to develop a solution which will have minimum disturbance on the traffic in the tunnel
and accordingly a solution was developed where additional cables were not placed inside the ballast
concrete. Under the tunnel ceiling the space is varying depending on location. In some locations, e.g.
where jet fans are located, there is plenty of space, but in other locations there is nearly no space. It
has been concluded that cables cannot be accommodated under the ceiling. The only space available
for additional cables is along the walls above the diminutive sidewalks.
Figure 9.3-1
shows the allowa-
ble space for cables with an acceptable distance from any traffic. In the 0.35 m wide and 1.90 m high
spaces indicated (blue colour) installations are accepted according to UK regulation (DMRB) and Ger-
man regulation (RABT). The Danish Road Directorate DRD has confirmed that installations in these
spaces are also accepted in Denmark. There will be no interference with (blocking of) any of the emer-
gency doors in the middle wall and cabinets in all the walls.
Structural strategies
Figure 9.3-1 Spaces available for installations such as external post tensioning
cables (blue colour) along upper part of all wall surfaces.
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The available spaces are assumed used for placing a number of external post tensioning cables. Ex-
ternal cables are often used for strengthening of existing structures and the solution is considered well
proven technology even though the use in an immersed tunnel may be unusual.
The cables will be exposed to the risk of accidental damage by impact from vehicles astray and will
also be exposed to damage in case of a fire. But as the cables are not necessary for the safety of the
structure these circumstances can be disregarded.
The number of cables to be accommodated in the narrow spaces available is of course limited. If nec-
essary, more space for more cables can be provided, e.g. along the middle wall by a certain (minor)
reduction of the width of the fast lane. The fast lane is however the slow lane during periods with two
directional traffic in one tube, why such reduction cannot be major. It is therefore instead proposed to
reduce the width of all three lanes if necessary for providing more space for the cables. A small reduc-
tion is not considered a problem by DRD as it has been used in several cases on Danish motorways
(one example is on the Kalvebod bridge in Copenhagen).
The external cables can be supplied by companies such as VSL, CCL, BBR and Freyssinet. As an ex-
ample, Freyssinet explains that the most common use of C range cable system in external prestress-
ing is based on the use of strands placed inside sections of thick HDPE tube, assembled by mirror
welding, which are injected with cement grout after tensioning. The use of a grease or wax (a flexible
corrosion resistant protective product) instead of cement grout is an alternative. It is however here rec-
ommended to use the cement grout due to the possibility of damages from traffic or fire and as it is
considered to provide a better protection of the cables in the sometimes wet/humid environment in the
tunnel. So that a duct can be removed without damaging the structure, the ducts are of double casing
type at deviators and anchor diaphragms. The HDPE tube runs inside a rigid metal lining that sepa-
rates the tendon from the structure and distributes the transverse loads caused by deviation.
In the Limfjord tunnel the deviators will only be controlling very small angle changes and friction losses
will be very small. Considering the circumstances for installation, the anchorage and deviator blocks
could be considered as tailor-made steel structures fixed to the existing structure by use of (a large
number) of drilled and glued-in anchor bolts. At the middle wall it could be considered to use pre-
stressed bolts and shear blocks or profiles passing through the wall. Anchor and deviator blocks can
also be constructed as reinforced concrete structures, but such will probably slightly limit the number
of cables compared to a steel solution. The concrete solution can in general benefit from standard
components and is therefore not depending on the design of a number of special tailor-made items
necessary for the steel solution. Concrete anchor and deviator blocks also depends on a large number
of drilled and glued-in anchor bolts and the distribution of forces to the many anchor bolts is more sim-
ple in a concrete block compared to a steel bracket type of anchor block.
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Figure 9.3-2 External post tensioning cables – intermediate tendon supports (VSL system shown).
The locations for anchor blocks shall allow a stepwise application of the forces into the structure.
Some cables in full length and other cables staggered where the tensile stresses are highest. Tension
behind the local anchorage shall be considered. The cables considered are very long; each in average
450 m. They are therefore supplied in half length and assembled with so-called moveable couples.
Different solutions for installation of additional cables have been investigated. The preferred solution
which has been developed and used as basis for the cost estimate is with concrete anchor and devia-
tor blocks and gives an additional prestressing force of around 80 MN. For further details refer to [10].
During a possible detailed design phase, it is recommended to investigate completely both a concrete
and a steel solution in order to compare possible effects to be achieved, necessary space require-
ments and costs of construction and maintenance.
The installation of cables and anchor/deviator/support blocks shall be executed during a complete clo-
sure of the tunnel tube where works are ongoing. In case of steel anchor and deviator blocks the time
needed for installation will be somewhat shorter compared to the casting of concrete anchor and devi-
ator blocks. The tensioning of all cables – and the following injection with cement grout – shall be post-
poned until after installation of all cables to allow a stepwise tensioning – a sequence of steps alternat-
ing between west and east tube. It is assumed that installations can be executed during relatively
short periods with closure of one tunnel tube (i.e. periods of 4 or 6 weeks of summer holidays) as indi-
cated in
Table 9.3-1.
The tensioning and grouting can be executed during night closures alternating
between tubes or during a weekend where the entire tunnel is closed.
Activity
Initial works west tube
Initial works east tube
Tensioning and grouting west
Tensioning and grouting east
Period in case of concrete an-
chor blocks
6 weeks
6 weeks
Period in case of steel anchor
blocks/brackets
4 weeks
4 weeks
Nights (alternating between west Nights (alternating between west
and east tube)
and east tube)
Nights (alternating between west Nights (alternating between west
and east tube)
and east tube)
Table 9.3-1 Assumed periods necessary for construction of additional prestressing in tunnel.
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9.3.3 Replace bearing blocks
The bearing blocks located in the northern portal building are dimensions 706 x 756 x 146 mm
3
. The
thickness of the grout pad under the bearing blocks is approximately 40 mm.
Figure 9.3-3 Existing bearing blocks in northern portal building.
These bearing blocks can be replaced with new bearing blocks with less height and with a Teflon layer
included. The possible reduction in height may not be more than approx. 20 mm, but more lowering
can be achieved by a small reduction in the height of the plinths below the bearing blocks. The height
of the grout pad can also be reduced from 40 mm to approximately 20 mm. The possible lowering of
the northern end of tunnel element V is thus at least say 90 - 100 mm (but circumstances as explained
in the following may prevent such a big vertical displacement unless some special measures are intro-
duced).
The use of bearing blocks with a reduced height would close the potential gap under the northern end
of the tunnel to some extent. Thereby more ground support could be mobilised and forces/stresses in
the tunnel in the longitudinal direction could be reduced. If the capacity of the cross section in the lon-
gitudinal direction was exceeded in the remaining lifetime (not assumed) this could be a relevant re-
medial proposal. But the proposal will also have some beneficial effect on limiting the crack width or
closing the cracks (by decreasing tensile stresses) to reduce future leakages, improve durability and
limit the extent of the injection campaigns. The new bearing blocks could be installed with load cells
providing current information regarding the load transfer and thereby be an important element in the
future monitoring of the tunnel structure (trigger values).
Temporary jacks would be used to exchange the bearing blocks and during this operation to provide
information regarding the current load and indirectly regarding the potential gap and the foundation
bed mobilization. The jacks could also be used as part of the monitoring system.
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Figure 9.3-4 Location of temporary jacks during replacement of bearing blocks.
The temporary jacks can only be placed south of the bearings in the gap between the small front wall
with the Omega seal expansion joint and the plinths. It means that the loads on the piles will be ap-
plied eccentrically.
Replacement of bearings by use of temporary jacks is often used, however mainly on bridges. It must
be regarded as well proven technology even if it is not common practice in case of an immersed tube
tunnel.
At least two important issues must be considered when deciding a possible reduced height of the
bearing blocks. The existing Omega seals can probably not adopt the maximum possible vertical dis-
placement equal the lowering of the tunnel. The Omega seals will probably define a too narrow limit
for this vertical displacement and as this is not assumed to provide enough effect, a radical new
Omega seal solution must be developed. The expansion joints in the road surfaces can without doubt
also not adopt the maximum possible vertical displacement and the installation of new expansion
joints in the road will influence the traffic. Even a minor vertical displacement may result in the con-
struction of some wedge-shaped transitions in the asphalt.
The replacement of the bearing blocks may be executed without much effect on the availability of the
tunnel. It must however be considered if load transfer from bearings to jacks and vice versa is consid-
ered critical in respect of safety for the tunnel users. But these operations can maybe be executed dur-
ing only night or weekend closures of the tunnel (the entire tunnel). The new Omega seal solution can
be executed without any (or much) influence on the traffic. New expansion joints in the road surfaces
will probably require the closure of each tunnel tube for approximately a week. New wedge-shaped
transitions in the asphalt can be executed in parallel during such week. As the vertical displacement of
the tunnel end will happen “over-night” some temporary transitions in the road surfaces will be neces-
sary (together with a reduced speed of vehicles during the period).
The cost estimate prepared for this solution attempts to include for a new Omega seal, new expansion
joints in roads, wedge shape transitions in asphalt and some temporary transitions to cover the short
period until the new joints are installed.
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10 Costs
Based on the recommendations from the Structural Expert Group, presented in Section 8 and 9 of this
report, combined with the budgets identified in the current 10-year budget for the Limfjord Tunnel, a 50
years budget has been developed.
The costs have been grouped under the following four headings:
A)
B)
Basic Operation & Maintenance
(Covers basic activities necessary to keep the tunnel in operation.)
Supplementary Inspection, Monitoring and Maintenance
(Supplementary activities recommended by the Structural Expert Group together with special
activities identified in existing 10 years budget.)
Major repairs/replacement
(Major repairs and replacement activities recommended by the Structural Expert Group together
with special activities identified in existing 10 years budget.)
Expert Group proposals – Retrofitting
(Preferred retrofitting projects proposed by the Structural Expert Group.)
Introduction
C)
D)
The tasks included under each of the four headings are shown in
Table 10.1-1.
Group
Task
A) Basic Operation & Maintenance
Consultant, General O&M - Average
Consultant, Inspections - Average
Maintenance contractor O&M - Average
Repairs - Average
Power, water, fees, safety drills etc.
Crack injection + fire proofing repair
B) Supplementary Inspection, Monitoring and Maintenance
Follow-up inspections every 3 years
Permanent monitoring, Installation and follow up
Cathodic protection, follow up
Inspections and analyses before Expert Group proposals
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Group
Task
Flooding - Analysis
Ship impact - Analysis
Monitoring of settlements (Fibre optic cable)
Maintenance and repair, structures
C) Major repairs/replacements
Cathodic protection, installation
Replacement of fire protection
Concrete repairs, inside
Replacement of Omega joint, south
Replace surfacing
Repair bearings and joints
Replace lighting
Replace M&E (ITS, UPS, PLC all inclusive)
Ventilation, renewal
D) Expert Group proposals – Retrofitting
Additional prestressing (year 2035)
Replace bearing blocks (year 2045)
Active horizontal compensation grouting (year 2064)
Table 10.1-1 Grouping of tasks included in the budget.
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Retrofitting Budgets
The budgets for the three retrofitting options are given in
Table 10.2-1.
Retrofitting option
Structural, Additional prestressing
Structural, Bearing blocks
Geotechnical, Compensation grouting
Table 10.2-1 Retrofitting Budgets.
Reference
[10]
[10]
[7]
Budget [mDKK]
35 – 40
35 – 40
200 – 240
 
The budgets from
Table 10.2-1
have been established through the following process:
Best estimate price for the technical part of the different retrofitting options has been given in
the different retrofitting reports (references appear in
Table 10.2-1).
A risk-workshop has been conducted by DRD with the results being presented in a Risk Anal-
ysis Report, reference [20]. Owners costs to project development, supervision and administra-
tion, termed PTA-costs, have been included in reference [21] together with a risk assessment
for each of the retrofitting options.
The output from the Risk Analysis Report is one price for each retrofitting option while
Table
10.2-1
provides a cost range for each option. The budget-interval from
Table 10.2-1
is the
preferred approach given the uncertainty at this stage of the design process.
The budget for the retrofitting options in
Table 10.2-1
is included in the 50-year plan (Section 10.3) by
the mean value of the budget-range provided in
Table 10.2-1,
e.g. the compensation grouting is repre-
sented by 220 million Danish kroner.
50 years budget
The 50 years budget is shown in
Figure 10.3-1.
As can be seen budgets for activities for groups A) and B) have been summarized under the heading
"Basic activities" as this includes all standard activities concerning operation, maintenance and retrofit-
ting to be carried out within the normal yearly budgets.
Budgets for extraordinary activities proposed in group C) and D) are shown individually.
The budget numbers are summarized in
Table 10.3-1.
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Figure 10.3-1 50 years budget for the Limfjord Tunnel based on current 10 years budget supplemented with activities recom-
mended by the Structural Expert Group.
Group
A)
B)
A)+B)
C)
A)+B)+C)
D)
A)+B+C)+D)
Table 10.3-1 Budget summary.
Average 2020-2029
[1000 DKK/year]
11.445
4.905
16.350
3.680
20.030
0
20.030
Average 2030-2069 [1000
DKK/year]
11.445
5.105
16.550
11.275
35.200
7.375
42.575
Sum 2020-2069
[1000 DKK]
572.250
253.250
825.500
487.800
1.313.300
295.000
1.608.300
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