Tunnel and Bridge Assessments Eastern Zone Assessment of the Effects of Tunnel Induced Settlement On Oxestalls Roadbridge Structure No. BR414 Doc Ref: 9.15.106 Folder 108 September 2013 DCO-DT-000-ZZZZZ-091500 Thames Tideway Tunnel Thames Water Utilities Limited Application for Development Consent Application Reference Number: WWO10001
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Tunnel and Bridge AssessmentsEastern ZoneAssessment of the Effects of Tunnel Induced Settlement On Oxestalls Roadbridge Structure No. BR414Doc Ref: 9.15.106
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Thames Tideway Tunnel Thames Water Utilities Limited
Application for Development ConsentApplication Reference Number: WWO10001
AECOM has been commissioned by Thames Tunnel to carry out an assessment of the effect the proposed tunnel would have on Oxestalls Road Bridge. This detailed bridge assessment is part of the Sub-Package 3c contract works for impact assessment of the proposed Thames Tunnel project.
Oxestalls Road Bridge is a single-span steel girder and composite concrete deck bridge with a rising approach structure on each side. Constructed in the late 1960’s, the bridge deck is reinforced concrete and is supported by 13No. longitudinal castellated girders at regular spacing. These have 4No. sections of cross bracing at intervals along their span. The outermost girders on either side of the span are skewed relative to the others. Details missing from archive information have been retrieved from site measurements, or an estimate was used. The approach structures feature a reinforced concrete deck slab and a series of reinforced concrete columns. Pad Foundations are founded on concrete piles.
The inspection for assessment (doc. No. 314-RI-TPI-BR414-000001, see Appendix 2) was carried out on the 28th February 2012. The structure was found to be in a fair condition. Surface corrosion was found to be wide spread over the steel sections of the structure, no section loss was observed. The carriageway surfacing is in poor condition over the structure, this is especially prevalent on the East approach. Some spalling was observed to the superstructure and substructure concrete; however, this is considered to be minor. A condition factor of 1.0 will be applied to all structural members in the assessment of Oxestalls Road Bridge.
This assessment has been undertaken in accordance with the Approval in Principle document No. 314-EA-TPI-BR414-000001 (see Appendix 1). The load effects, for the main span, have been determined by modelling the structure as a grillage in LUSAS, using linear elastic methods, and by using hand calculations. The approach structures have been modelled as a linear elastic plane frame in SAM.
Settlement applied to the structure was in a form of displacements and rotations of the foundation supports induced by the settlement of the soil. The effect of these displacements on the modelled members of the structure was compared against their sectional capacities (calculations in Appendix 4), i.e. utilisation = applied stress / ultimate stress.
The maximum main span effect was due to axial compression of the longitudinal girders, caused by friction at the bearings resisting the induced movements. This temporary effect caused a utilisation of 4.66% which is below the 10% threshold outlined in the Approval in Principle for a volume loss of 1.0%. The approach structures were found to be over 170% utilised for HA, dead load, and super imposed dead load in the hogging regions of the structure. This indicates these sections are cracked under normal working load and the structure is acting as if each span is simply supported, and hence, would not be affected by settlement effects. A number of services were identified in the North footway. These were assessed qualitatively not to be at risk of applied settlements.
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The only recommended mitigation measure resulting from this assessment is standard routine monitoring, as per any tunnelling construction project, before, during and after the Thames Tunnel construction to ensure actual movements are less than those used in this assessment.
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2 Introduction
AECOM has been commissioned by Thames Tunnel to carry out an assessment of the effect the proposed tunnel would have on Oxestalls Road Bridge. This detailed bridge assessment is part of the Sub-Package 3c contract works for impact assessment of the proposed Thames Tunnel project.
The main objective of the project is to identify any structural or serviceability implications that may result from proposed tunnelling works in the vicinity of the existing infrastructure.
Oxestalls Road Bridge is the most recent bridge to be constructed over the Grand Surrey Canal. It was constructed downstream from the entrance lock of the canal. The bridge and surrounding estate were built in the 1960's, when the canal was still in use. The canal beneath the bridge has been filled in since construction of the bridge and the land has been reclaimed.
Oxestalls Road Bridge is a single-span castellated steel plate girder and composite concrete deck bridge with a rising approach structure on each side. The bridge deck is reinforced concrete and is supported by 13No. longitudinal castellated girders, mostly, at regular spacing. These have 4No. sections of cross bracing at intervals along their span. The outermost girders on either side of the span are skewed relative to the others. The approach structures are formed from reinforced concrete piles and columns supporting a reinforced concrete slab. The approach columns are placed in rows of three with varying spacing between reinforced concrete abutment walls, spanning the full width of the slab.
Archive information has been provided for the structure from the London Borough of Lewisham. Some structure details have not been sourced for the assessment so details, such as pile depth, have used a ‘best estimate’ approach. After reviewing these details an inspection for assessment was performed (see the inspection report in Appendix 2) to verify the condition of the structure.
The settlement of the ground due to the proposed tunnel was calculated using a Greenfield Settlement analysis. The calculated settlements were taken from the analysis and applied directly to the computer model. The resulting structural effects were then compared against the sectional capacity of the affected members.
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3 Structure Details
3.1 Superstructure
Oxestalls Road Bridge is a steel and concrete composite structure, consisting of a reinforced concrete deck and 13 No. simply supported pre-cambered longitudinal castellated steel main girders. There are four transverse cross-bracing trusses, formed from 90° steel angle sections. The main I section girders have an overall dimension of 927mm by 312mm. The bridge has a span of 21.2m and is founded on elastomeric bearings which sit on top of a reinforced concrete abutment and bearing shelf, which totals 3.4m in height and 16.5m in width. Joints are located in the concrete deck slab at each end of the span, above each bearing shelf. The metallic parapet railings are founded on concrete upstands.
The approach structures to the East and West are of reinforced concrete construction. The deck slab is supported by rows of three circular columns measuring approximately 450mm diameter each. The approach end is supported on a reinforced concrete abutment wall spanning the width of the slab. The approach structure has masonry infill panels.
Photograph 1 Oxestalls Roadbridge looking North
3.2 Substructure
The structure abutments are of reinforced concrete composition. The West abutment sits on a concrete footing which is founded on two rows of 7No. concrete piles spaced at 2.59m centres. The East abutment sits on a concrete footing which is founded on 17No. staggered concrete piles spaced at 1.22m centres. The approach structures are founded on a
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series of concrete footings and concrete piles located under the supporting columns.
3.3 Articulation
The main bridge span is simply supported with expansion joints at either end. The main girders are free to expand and contract on the steel plate bearing system installed between each girder and the bearing shelf. The bearing plates measure 300mm by 350mm by 50mm. The approach span deck is continuous over the column supports, with expansion joints at either end.
Asphaltic plug joints are located in the road surface above the deck joints.
3.4 Spans
The bridge appears square to both the East and West abutments and has a span of 21.2m. The two way spanning approach spans curve on plan up to the main deck span. The West approach spans over 8 rows of columns and the East approach spans over 6 rows of columns.
3.5 Parapet
The parapets comprise steel railings founded on a concrete upstand at the edge of the deck slab. The parapet is 1.04m total height and the upstand is 170mm high.
3.6 Surfacing
Asphaltic surfacing layers are placed directly upon the concrete deck slabs. It is not possible to determine any depth or materials of the various layers.
3.7 Drainage
The drainage system comprises a series of drain holes adjacent to the road kerb line, these pass through the deck slab, it’s not clear where the drainage system directs the collected water.
3.8 Services
Utility records indicate that two 8” steel low pressure gas mains, a 8” water main and two 4” steel electricity service pipes (General Post Office and London Electricity Board) are located in the North footway of the bridge and are packed in sand.
3.9 Record information
Record information has been provided as follows;
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Drawing Number
Drawing Name
1 Road Location Plan
2 Longitudinal Profile and Finished Levels
3 Cross-profiles of road and bridge
4 Section Sheet 1 (West)
5 Section Sheet 2 (East)
6 South elevation
7 North elevation
8 Foundation Location Plan and Drainage
9 Piling Layout
10 Retaining wall 1
11 Retaining wall 2
12 Retaining wall 3
13 Retaining wall 4
14 Retaining wall 5
15 Retaining wall 6
16 West abutment
17 East abutment
18 Ground slab and foundations under West approach road
19 Ground slab and foundations under East approach road
20 West approach road cols and pile caps sheet 1
21 West approach road cols and pile caps sheet 2
22 East approach road cols and pile caps
23 Canal profile to East abutment
24 West approach road general arrangement
25 West approach road bottom steel
26 West approach road top steel
27 East approach road general arrangement
28 East approach road bottom steel
29 East approach road top steel
30 Main span general arrangement
31 Main span slab reinforcement
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32 Main span layout of bridge steelwork
33 Main span details of castella beams
34 Petrol interceptor pit and catchpit details
35 Balustrade details
36 Brick manhole details
BE10364-1 Oxestalls road bridge (void beneath W. Approach ramp deck)
BE10364-2 Oxestalls road bridge (void beneath W. Approach ramp deck)
BE Survey 1 Bridgeguard
BE Survey 2 Oxestalls road bridge general arrangement
Table 1. List of drawings to be used in the assessment
3.10 Maintenance and Modifications
Maintenance history has been provided as follows;
- General Assessment Report, 14th July 2009
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4 Inspection for Assessment Findings
4.1 Purpose
AECOM has been commissioned by Thames Tunnel to carry out an Inspection for Assessment of Oxestalls Road Bridge. This detailed bridge assessment is part of the Sub-Package 3c contract works for impact assessment of the proposed Thames Tunnel project.
4.2 Methodology
Inspection of the bridge was undertaken by AECOM on the 28th February 2012.
The main objective of the project is to identify any structural or serviceability implications which may result from proposed tunnelling works in the vicinity of the existing infrastructure. The inspection for assessment has been focused specifically at the elements that could potentially be affected by the proposed Thames Tunnel construction, however inspection of other elements was undertaken as well and observations included for the asset owner’s consideration.
Below a brief summary of the inspection is presented. More details relating to observations made during the inspection work are included in Appendix 2.
4.3 Superstructure
Generally, the bridge was in fair condition, with some signs of deterioration throughout.
A large amount of surface corrosion is visible on some of the outer longitudinal span girders and their bearing plates. Surface spalling on the structural concrete of the superstructure elements was observed in several locations. This surface breakaway has resulted in the exposure of reinforcement steel in many places. Concrete spalling and efflorescence was observed adjacent to some of the weep holes in the concrete structure, where water runoff is also evident.
The carriageway and footways were observed to be in poor condition. Excessive cracking was found on the Asphalt surface of the road and in the paving slabs of the footway. Large transverse cracks in the carriageway are visible at the location of joints in the concrete of the superstructure. Significant cracking and breakup of the road surface is particularly evident on the East approach to the bridge. Large pot holes are forming in this area due to the surface deterioration. The underside of the approach structures could not be viewed due to the masonry infill panels surrounding the structure.
4.4 Substructure
Some degradation of the abutments was evident in the form of spalling of the concrete face. This appears to have been caused by water permeating through the joints in the deck at the positions of the span supports. Water runoff has caused staining of the abutment faces. It is promoting the
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growth of organic material and the deposition of minerals on the face of the concrete.
4.5 Foundations
The foundations are buried and could not be inspected. At present the structure is showing no signs of distress that could be attributed to a failure or excessive movement of the foundations.
4.6 Conclusions and Recommendations
The structure was found to be in fair condition. Even though surface corrosion was found to be wide spread over steel sections of the structure, no section loss was observed. The carriageway surfacing is in poor condition, this is especially prevalent on the East approach. Some spalling was observed to the superstructure and substructure concrete, this seems to be a result of water ingress into the concrete. The exposed reinforcement appears to be very close to the surface of the concrete, indicating poor design/construction.
Based on the condition of the structural members inspected a condition factor of 1.0 will be applied to all structural members in the assessment of Oxestalls Road Bridge.
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5 Assessment Methodology
This assessment has been undertaken in accordance with the Approval in Principle document No. 314-EA-TPI-BR414-000001-AC, included in Appendix 1. Ground movements calculated from the Greenfield settlement analysis are applied at the bearing support of the modelled structure. The resultant load effects on the structure are compared against sectional capacities of the relevant members. Where this approach is not possible empirical methods will be used.
5.1 Analysis of Structure
The main span load effects have been determined by modelling the structure as a grillage in LUSAS, using linear elastic methods, and by using hand calculations.
Figure 1 Main span Grillage in LUSAS
The approaches have been modelled by creating a linear elastic plane frame model, of a section though the east approach, in SAM and using hand calculation methods. The alignment of the tunnel will affect longitudinal and vertical members in the permanent case, so a two dimensional analysis was used.
Figure 2 Approach Plane Frame in SAM
As the main span is simply supported there will be no permanent stresses induced. The deck will slide at the bearings to accommodate the movement of abutments induced by the tunnelling action. Before the deck can slide, the friction due to the dead loads between the bearing plate and the bed stones must be overcome. As the friction prevents the deck from sliding, it will cause the deck to shorten creating an axial stress.
The stress will be relieved either by continued movements of the abutments or vibrations of the deck from the live load. At some point the
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friction required to resist the movement of the deck will be overcome by the rotation of the abutments. Alternatively, the vibrations caused by the live load passing over the structure may ‘bounce’ the deck allowing movement at the bearings.
All 13 girders have been modelled using dimensions taken from the site inspection, material properties have been taken from archive information, or where not available, assuming standard 1960’s values. The deck slab has been given conservative or ‘worst case’ properties from supplied archive information. Where possible, members are placed at the centre line of the section they represent. Member connections have been assumed to be rigid. Conservatively, the connection between the bearing plate and girders has been assumed to be fully fixed for a moment check, meaning an unrealistically high force will be induced in the elements. The foundation piles have been omitted from the analysis and a nominal footing has been assumed. This approach mitigates some of the uncertainty about the structure and is conservative.
The approach spans have been assessed using the east approach, inner radius, dimensions. The plane frame model has been assigned section properties to represent the full width of the structure. Therefore, the deck elements are modelled with a 15m wide and 355mm deep section and each column member represents 6 columns. Rigid offsets have been used at deck level to represent the spreading action of the coned support columns, and the tops of the columns are given a relatively higher stiffness to represent the top cone detail. The calculated ground settlements are applied directly to the column bases.
All members will be modelled using beam elements with appropriate section and material properties assigned. The calculated settlements are applied as displacements and rotations to the member supports. The force induced in the members as a result of this displacement and rotation is then calculated and compared against a calculated section capacity.
5.2 Calculation of Settlement Trough
Site ground conditions were identified from borehole logs obtained from the British Geological Society. This information was used along with the proposed tunnel size and alignment in a Greenfield settlement analysis to produce the settlement troughs (see Appendix 3).
5.3 Application of Settlement
Load applied to the structure was in a form of displacements and rotations of the girder supports induced by the settlement of the soil. The calculated displacement and rotation applied to the main span supports takes account of the lever arm formed from the offset from the bearing shelf to the foundation bases where the settlement has been calculated. As the tunnel alignment runs close to the centre of the span the rotation and displacement of the foundations will be the same on each abutment.
The transverse settlement, or bow wave effect, causes the whole structure to deflect away from the tunnel as it approaches and then settle back to a horizontal position in the permanent case. As the main span is a simply
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supported, transversely stiff, section this will have little to no effect on the bridge elements. Hence these effects have not been considered.
5.4 Calculation of Section Capacities
When calculating the ultimate capacity of a section, the factor γf3 = 1.1 has
been included for all elements along with the appropriate γm for the material (from BD 56).
A condition factor of γc = 1.0 has been assumed in the assessment of all elements. This is justified as the structure is, in general, without any major signs of distress. For the Inspection Report refer to Appendix 2.
The load effects from the analysis are translated into maximum stresses and forces induced in the relevant sections and compared against the ultimate stress or force of the relevant section. The elements are checked for bending, and where required axial effects and shear. The utilisation check is a comparison and does not reflect the actual value of stress in the section but simply the change in stress.
5.5 Utilities & Drainage
Utility information has been provided by Thames Tunnel and the London Borough of Lewisham for the structure, and as a result, two 8” steel low pressure gas mains, a 8” water main and two 4” steel electricity service pipes have been identified in the North footway. Due to the age of the structure it’s unlikely that any sensitive services are carried by the bridge i.e. cast iron pipes. From drawing No.8 no drainage pipes cross the span.
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6 Assessment Results Summary
6.1 Superstructure & Substructure
The following table summarises results obtained during the assessment process for the main span superstructure. Detailed calculations are included in Appendix 4 of this report.
The utilisation shown below expresses the ratio of a factored load effect to the ultimate capacity of the element and is derived from the following equation:
Utilisation = FactoredLoadEffect
UltimateLimitStateγ�∗ γ
��
=FactoredLoadEffect
ULSCapacity
The results shown below, in Table 1, are utilisations of the main steel girders when subjected to permanent tunnel settlements at 1.0% volume loss. The applied bending moment has been extracted from the LUSAS model and compared to a bending capacity calculated for the beam only, ignoring composite action, using BS5400-3 and BD56/10. The 1.67% utilisation is minimal considering many conservative assumptions have been made in the assessment.
Location Effect Applied Max Utilisation
Main Girder Axial 9.96 213.85 4.66%
Main Girder Bending 34.19 2049.64 1.67%
Table 1; Utilisation of Main Girders at 1.0% Volume Loss
The applied axial stress has been calculated empirically using the dead load of the structure. This applied axial stress represents the maximum axial stress which can be achieved in the main girders before they slip on their bearing plates. As the calculated settlement causes a theoretical stress higher than that required to cause bearing slippage, the movement caused by the inward rotation of the abutments in the permanent case will be relieved by movement of the bearing plates.
The load effects above are not coincident with live loads on the bridge which will have the effect of relieving the loads built up from the abutments settling.
The calculated settlement was applied to the column bases in the plane frame model of the East approach structure, this lead to an unrealistically high bending utilisation in the deck section. It was noted that the deck does not meet current design requirements for minimum steel reinforcement content. Dead loads and superimposed dead loads were applied to the structure and HA loading was applied over two spans. It was found that the hogging utilisation in the deck slab for this loadcase was over 170% in the hogging region. This indicates the deck concrete has cracked in the hogging regions. The cracking will ultimately mean the deck behaves as a series of simply supported spans, and hence, no moment will be induced as a result of the differential settlement of columns.
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6.2 Utilities
As the bridge is simply supported, and the tunnel is aligned close to mid-span, the effect of tunnel induced settlements on the carried services will be negligible. There was no evidence of further services during the inspection of the structure. However, due to the age of the structure it’s unlikely that any sensitive services are carried by the bridge i.e. cast iron pipes.
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7 Discussion of Results and Conclusions
7.1 Superstructure & Substructure
As Oxestalls Road Bridge is simply supported the effects of settlement will not add to the permanent stresses in the structure. As the bridge has a relatively short span, and abutment height, the settlement and rotation of the abutments is relatively small.
Theoretically there will be no stresses induced in the main span by the settlement as the bridge deck allows for longitudinal movements and rotations. This allowance comes from the bearing plates located between the girders and bearing shelf and expansion joints in the reinforced concrete deck. In reality the friction between the bearing plates and the bed stones will resist a certain amount of movement. The coefficient of friction used between these two surfaces in the assessment is conservative.
Once the longitudinal movement exceeds that which can be resisted by the friction at the supports, or live load travels over the bridge, the deck will move at the bearings and the stresses will be relieved. The stress in the bridge deck is dependent on the maximum friction force at the bearings and not the amount of movement induced by the settlement. Therefore, the maximum axial stress will be the same for all values of volume loss. It is also worth noting that the level of longitudinal movement experienced by the bridge deck is less than two and a half millimetres for each abutment.
For low volume losses the longitudinal movement induced by tunnelling will be less than the maximum strain that can be realised in the bridge deck before bearing slippage. In this case, the induced stresses will be lower than those calculated in Appendix 4. As the maximum friction force is never achieved, the maximum strain and hence stress is never reached in the deck. As the friction is not overcome the bridge deck will not move due to the settlement alone. The stress will be relieved by the effect of vibrations of the live load that will ‘bounce’ the bridge deck free.
As a conservative check the supports were fixed on the grillage model, and the rotations induced in the abutments as a result of 1.0% volume loss were applied at the base of the girders. The induced bending moment from the LUSAS model was compared with the bending capacity calculated for the section using BS5400 and BD56/10. The utilisation found was 1.67%. Conservatively, no composite action was taken into account when calculating the ultimate capacity of the section. This means that in the highly unlikely case of the bearing plates seizing solid the girders would still be able to accept the induced moment at 1.0% volume loss. The curvature of the girders has been ignored for this assessment. It is considered this would have a minimal effect of the results.
The initial calculations found the longitudinal girders above the proposed tunnel route to be stressed below the first acceptance criteria of 10%. It was assumed that the strains caused by the friction force were evenly applied to all four of the longitudinal girders.
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The calculated settlements were applied to the East plane frame column supports for a 1% volume loss. This action set up an unrealistically high bending utilisation for the differential settlement experienced. In order to gauge the level of stress in the approach deck under working loads, HA, dead load and super imposed dead load were applied to the model. Resulting in a utilisation for bending in the hogging region of over 170%. This indicates the concrete in the hogging region must be cracked from working loads on the structure. As the structure is cracked in this region there will be no moment carry over from one span to the next. In effect a pinned support has been created. If the approach spans are treated as simply supported, individual spans, then settlement effects will not induce a stress due to differential settlement of the column foundations. The percentage of steel in the concrete deck is low compared with modern standards and wouldn’t meet current minimum steel requirements. Based on these assumptions the reinforced concrete approach structures will not be affected by the tunnel induced soil settlements.
7.2 Utilities & Drainage
As the tunnel runs close to mid-span of the bridge (no differential settlement between abutments) and the span is relatively small, the effect of tunnel settlements on carried utilities will be negligible. The indicated steel services in the North footway run the entire length of the span and the East and West approach structures. Any settlements experienced at mid-span will be gradual across the length of the approach structures. No further services were identified during the inspection. However, due to the age of the structure it’s unlikely that any sensitive services are carried by the bridge i.e. cast iron pipes.
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8 Recommendations
The stress increase we have identified in this assessment is less than the threshold value stated in the Approval in Principle document. It is worth noting that the stresses only represent a change in stress and do not relate to the actual level of stress in the members. The increase in stress is also not coincident with live load so it is safe to say that the additional stress does not exceed the dead plus live load stress level of the bridge.
Given the low value of stress induced in the bridge deck and the temporary nature of these effects it is highly unlikely that the proposed tunnelling will have an impact on the structure. It is also worth noting that the findings of this report are based on conservative values of volume loss structure geometry and coefficient of friction between the bridge bearing plates and bed stones.
The only recommended mitigation measure resulting from this assessment is standard routine monitoring, as per any tunnelling construction project, before, during, and after the Thames Tunnel construction to ensure actual movements are less than those used in this assessment.
Assessment Report Appendix 1 03/01/2013
APPENDIX 1 – Approval in Principle
Document No. 314-EA-TPI-BR414-000001-AC
Assessment Report Appendix 2 03/01/2013
APPENDIX 2 – Inspection Report
Document No. 314-RI-TPI-BR414-000001-AB
Assessment Report Appendix 3 03/01/2013
APPENDIX 3 – Predicted Settlement Troughs
Graphs are provided for vertical and horizontal settlement, as well as, ground slope and tensile strain at 1.0% and 1.7% volume loss. Each of the above cases will be provided at base of the foundation level and at ground surface level.
Each case begins with a layout plot which depicts the depth to tunnel centre line and its location relative to the foundation footprint. If the tunnel is located at mid-span, then only a single foundation will be shown for clarity. The second graph shows settlement and horizontal movement from the tunnel centre line. This graph can be used to read off horizontal and vertical movements at various distances from the tunnel axis. The third graph depicts the slope of the settlement trough and the horizontal tensile strain, which can be read off at various distances from the tunnel central axis. The final graph shows a detailed view of the vertical settlement and values at points of interest, such as edges of foundation.
The following settlement cases are provided in this report;
Inspection for Assessment Report Oxestalls Road Bridge Structure No. BR414
THIS REPORT INCLUDING THE DRAWINGS AND OTHER SUPPORTING DOCUMENTATION IS PROVIDED FOR THE PURPOSE OF IDENTIFYING AND AGREEING THE LIKELY EFFECTS OF THE CONSTRUCTION OF THE THAMES TUNNEL ON THE ASSETS AND INFRASTRUCTURE OF THE PARTY IN RECEIPT OF THIS REPORT AND FOR THE PURPOSE OF SECURING APPROVAL IN PRINCIPLE TO THE DESIGN OF THE THAMES TUNNEL. THE REPORT IS CONFIDENTIAL TO THAMES WATER AND THE INTENDED RECIPIENT AND THEIR CONSULTANTS [APPOINTED WITH THE AGREEMENT OF THAMES WATER]. THE REPORT SHALL NOT BE PROVIDED TO ANY THIRD PARTY WITHOUT THE EXPRESS WRITTEN PERMISSION OF THAMES WATER UTLIITIES LIMITED.