Application Reference Number: WWO10001 Tunnel and Bridge Assessments · 2016-05-05 · Tunnel and...

Tunnel and Bridge AssessmentsEastern ZoneTransport for London Road Management Services (A13) plc Britannia BridgeDoc Ref: 9.15.76

Folder 104 September 2013DCO-DT-000-ZZZZZ-091500

TfL

Road

Man

agem

ent S

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(A13

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Brit

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Thames Tideway Tunnel Thames Water Utilities Limited

Application for Development ConsentApplication Reference Number: WWO10001

307-RG-TPI-BR409-000001

Assessment Report Detailed Bridge Assessments Sub-Package 2C

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Thames Tunnel

Assessment Report Britannia Bridge

List of contents

Page number

1 Introduction ...................................................................................................... 6

1.1 Project Description .................................................................................. 6

1.2 Works at Britannia Bridge ........................................................................ 6

1.3 Scope of Assessment .............................................................................. 6

1.4 Other Third Party Interface/ Related Assessments .................................. 7

2 Structure Details .............................................................................................. 7

2.1 Description of Structure ........................................................................... 7

2.2 Structure Type ......................................................................................... 7

2.3 Foundation Type ...................................................................................... 8

2.4 Span Arrangements ................................................................................. 8

2.5 Articulation Arrangements ....................................................................... 8

2.6 Year of Construction ................................................................................ 9

3 Inspection and Data Collection ....................................................................... 9

3.1 Inspection Summary ................................................................................ 9

3.2 Reference Data ....................................................................................... 9

3.3 Adequacy of Data and Assumptions ...................................................... 10

4 Ground Movement Assessment ................................................................... 11

4.1 Method of Ground Movement Calculation ............................................. 11

4.2 Ground Conditions ................................................................................. 13

4.3 Ground Movement Results .................................................................... 13

5 Structural Assessment .................................................................................. 19

5.1 General .................................................................................................. 19

5.2 Reference Documents ........................................................................... 19

5.3 Structure Records .................................................................................. 19

5.4 Assumptions and Codes used in the Assessment ................................. 19

5.5 Structural Assessment Methodology ..................................................... 20

5.6 Assessment Results .............................................................................. 23

6 Monitoring and Mitigation ............................................................................. 26

6.1 Route-Wide Monitoring .......................................................................... 26

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6.2 Asset-Specific Monitoring and Mitigation ............................................... 26

7 Conclusions and Recommendations ........................................................... 27

8 Further Work ................................................................................................... 27

Appendix A – Location Plan and Proposed Tunnel Alignment .......................... 28

Appendix B – Settlement Trough .......................................................................... 29

Appendix C – Certificate of Assessment and Checking (Structural) ................. 30

Appendix D – Certificate of Assessment and Checking (Geotechnical) ............ 31

List of Figures

Figure 1: Britannia Bridge – south elevation ............................................................... 8

Figure 2: Longitudinal Vertical Settlement Profile ..................................................... 14

Figure 3: Bridge plan with the location of points used for ground movement calculations and direction of ground strain calculations. .......................... 15

Figure 4: Bridge plan with the location of further directions of ground strain calculations perpendicular to the tunnel alignment. ................................. 15

Figure 5: Longitudinal Wave Vertical Settlement Profiles at -6m as the TBM progresses close to Britannia Bridge. ...................................................... 16

Figure 6: Longitudinal Wave Parallel Horizontal Displacement at -6m as the TBM progresses close to Britannia Bridge. ...................................................... 17

Figure 7: Longitudinal Wave Perpendicular Horizontal Displacement at foundation level as the TBM progresses close to Britannia Bridge. ........................... 18

Figure 8: Horizontal Displacement Contours around the bridge structure (plan view) in the Permanent Case ............................................................................ 21

Figure 9: Horizontal Displacement Contours around the bridge structure (plan view) in the Transient Case ............................................................................... 21

Figure 10: Longitudinal Wave Maximum Structure Strain as the TBM progresses close to Britannia Bridge (1) .................................................................... 24

Figure 11: Longitudinal Wave Maximum Structure Strain as the TBM progresses close to Britannia Bridge (2 - Scaled with respect to the limiting tensile strain criteria (0.05%) depicting negligible damage as set out by Burland (1995)) ..................................................................................................... 24

List of Tables

Table 1: Britannia Bridge brick arch dimensions ......................................................... 8

Table 2: Calculated ground movement due to tunnelling works at Britannia Bridge. 14

Table 3: Britannia Bridge XDisp Output Data (1) ...................................................... 23

Table 4: Building/Structure Damage Risk Classification Burland .............................. 25

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List of abbreviations

CSO Combined Sewer Overflow

TT Thames Tunnel

PBA Peter Brett Associates

STW Sewage Treatment Works

EPB Earth Pressure Balance

TBM Tunnel Boring Machine

TfL Transport for London

RMS Road Management Services (A13) plc

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1 Introduction

1.1 Project Description

Thames Water is currently progressing with its planned London Thames Tideway Improvements programme. The improvement works consists of construction of two new tunnels, the Thames Tunnel and the Lee Tunnel, together with a programme of Sewage Treatment Works (STW) upgrades.

Construction of the Thames Tunnel (TT), stretching approximately 23km under the River Thames from West London to East London, is due to commence in 2014. The Tunnel will intercept the flow from the most polluting Combined Sewer Overflows (CSO) of the existing system. The planned alignment runs mainly beneath the River Thames at depths of up to 40m below the river bed in order to minimise the potential impact on third party assets.

The main Thames Tunnel is currently planned to be 7.2m internal diameter with a primary and secondary lining giving an effective 8.5m external diameter with an excavated cut diameter of 8.8m. A number of smaller additional tunnels are required to connect the existing CSOs to the main tunnel.

As part of the works, Thames Tunnel Project Team has appointed Peter Brett Associates (PBA), and their sub-consultant Arup, to undertake an assessment of the effects of tunnelling-induced ground movement on Britannia Bridge.

1.2 Works at Britannia Bridge

The main Thames Tunnel is to be constructed west of the Britannia Bridge running northeast between Limehouse and Bromley, at a depth of 55.3m below ground level. The excavated diameter of the tunnel will be 8.8m, internal finished diameter 7.2m.

Refer to the drawing included in Appendix A for a location plan of the bridge and the proposed alignment of the Thames Tunnel.

1.3 Scope of Assessment

The scope is limited to assessing Britannia Bridge for the effects of ground movements due to the proposed construction of the Thames Tunnel in accordance with the Approval-in-Principle document no. 307-EA-TPI-BR409-000001-AD.

The assessment has determined the differences in load and serviceability effects due to the tunnelling works and does not represent a full assessment of the capacity of the structure.

Reference should be made to the Approval-in-Principle, which has been issued separately to this document, for the detailed scope of work and methodology and input parameters for the assessment.

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1.4 Other Third Party Interface/ Related Assessments

The adjacent steel utility bridge, the steel steps, the Limehouse Cut canal walls, and the retaining walls running parallel to the canal are the subject of separate detailed assessments commissioned by Thames Tunnel.

2 Structure Details

2.1 Description of Structure

The Britannia Bridge is a brick arch bridge of one span carrying the A13 (Commercial Road) over the Limehouse Cut. The structure is located in the London Borough of Tower Hamlets.

The bridge is owned by Transport for London but it is operated and maintained by Road Management Services (A13) plc (RMS) under a 30-year DBFO contract. The bridge has the following references:

Name: Britannia Bridge

Structure Number: A13/2.90 – Brick Arch Span

A13/2.90/3 – Gas Main Iron Plates

A13/2.90/A – R.C. Footway Extension South

A13/2.90/B – R.C. Footway Extension North

For photographs and description of the condition of the structure, reference should be made to the Inspection Report 307-RI-TPI-BR409-000001.

2.2 Structure Type

The bridge consists of a skewed brick arch. The clear square span between east and west abutment at the arch springing level is 9.1m. The skew span is roughly 10.5m and the angle 30 degrees. The total width of the brick arch measured along the face of the east abutment is 22m.

There are large metal plates in the soffit of the arch on the north side of the bridge where the gas main cast iron duct was cut into the arch structure. The cast iron duct is protected from the top by a reinforced concrete slab supported by the brick arch on either side of the opening.

Each side of the bridge has been widened with reinforced concrete extensions spanning approximately 16m between east and west abutments and partially supported by the brick spandrels and arch barrel. For key dimensions of the brick arch refer to Figure 1 and Table 1 below.

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Figure 1: Britannia Bridge – south elevation

Table 1: Britannia Bridge brick arch dimensions

Dimension Units

Number of rings (A) No 5

Thickness of arch rings (crown) (A1) m 0.58

Square span of arch (B) m 9.1

Skew span of arch m 10.5

Rise – spring to crown (C) m 2.1

Depth of cover (D) m 1.1

2.3 Foundation Type

No information is currently available on the foundations of the arch abutments. It is expected that the foundation will be either masonry or concrete. There is no evidence of settlement or other foundation problems.

For the purposes of assessment of ground movement effects due to construction of the tunnel, a sensitivity analysis has been undertaken on foundation depths between 0m and -6m. The foundation depth that gives the worst case results within this range has then been used in the assessment of the effects of ground movement.

2.4 Span Arrangements

The square span of the arch is 9.1m

The skew span is roughly 10.5m and the angle 30 degrees.

The effective span of the reinforced concrete footways is 16.45m

2.5 Articulation Arrangements

The main span of the bridge acts as a brick arch without movement joints.

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The reinforced concrete footways are simply supported on rubber bearings at both ends and partially supported by the brick arch which provides transverse stability. They are of semi-integral construction with fill placed directly against the back of the footway structure.

2.6 Year of Construction

The bridge is part of the A13 Commercial Road and was originally built in 1850 to span the Limehouse Cut.

In 1870 a cast iron gas diaphragm duct was cut into the brick arch and in 1921 the bridge was widened at the north and south ends using a concrete slab and beam construction.

Between April 1989 and April 1990 the bridge was partially reconstructed involving the replacement of the concrete footpath extensions on both north and south sides of the bridge.

3 Inspection and Data Collection

3.1 Inspection Summary

A visual inspection of the bridge was carried out from publicly accessible areas on 20th February 2012. The inspection found that the brick arch was in a fair condition and the reinforced concrete footway extensions were in good condition as far as could be visually inspected.

Reference should be made to the Inspection Report 307-RI-TPI-BR409-000001 for a more detailed description of the condition of the structure and photographs. A summary of the findings are given below:

A condition factor of 0.8 for assessment of the arch spans and 1.0 for assessment of the reinforced concrete footways will be adopted,

There are no finishes, or structural details, that are particularly sensitive to the effects of foundation movements,

Active water ingress was noted at one location on the east abutment. Refer to section 6.2 of the Inspection Report. This was also noted in the WSP Principal Inspection Report [8]

The cracking and movement of the wall to the north east of the structure as noted in [8] has not been repaired.

3.2 Reference Data

The following record information was made available for Britannia Bridge.

[1] A13/TH/EXR/06/906 Britannia Bridge No A13/2.90; Principal Inspection (1992)

[2] A13/TH/EXR/06/914 Approval in Principle for the Assessment of the Brick Arch only of Britannia Bridge No A13/2.90 (1992)

[3] A13/TH/EXR/06/919 Defect Assessment – Service Ducts (1994)

[4] A13/TH/EXR/06/920 Defect Assessment – Piers, Concrete Slab, Drainage, Waterproofing and Parapets (1994)

[5] A13/TH/EXR/06/921 Defect Assessment – Bearings, Expansion Joints

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(1994)

[6] A13/TH/EXR/06/922 Inverts or Aprons, Abutments, Arch Ring, Spandrels, Surfacing, Walkways (1994)

[7] 99C011/1/A Principal Inspection Report (1999)

[8] 10401280/A13-2.90 Principal Inspection Report (2006)

Record drawings were also made available providing good dimensional information on the existing structure. For a full list of drawings reference should be made to the Approval-in-Principle document no. 307-EA-TPI-BR409-000001-AD.

The line and level of the tunnel has been taken from the following alignments:

Abbey Mills Route – Provisional Horizontal Alignment for Phase 2 Consultation. CAD File Ref: 100-DO-DES-00000-017402-AL

Abbey Mills Route – Provisional Vertical Alignment for Phase 2 Consultation. CAD File Ref: 100-DO-DES-00000-017423-AI

3.3 Adequacy of Data and Assumptions

Below the substructure, foundation details are unknown. As such and as per Section 2.3, for the purposes of this assessment a sensitivity analysis has been undertaken on foundation depths between 0m and -6m. The foundation depth that gives the worst case results within this range has then been used in the assessment of the effects of ground movement.

There are large metal plates in the soffit of the arch on the north side of the bridge where the gas main cast iron duct was cut into the arch structure. It is assumed that the original part of the brick arch was broken out and replaced with metal plates. Existing drawings, included in the Inspection Report, show a concrete slab over the area of the gas main and metal plates, and a thickness of brickwork or concrete between the duct and lower plate. On this basis, the area is considered to behave similarly to the remainder of the arch. Thus, the effects will be assessed in accordance with Burland (1995) methodology similarly to the brick arch. It is noted that this part of the structure could be more sensitive to the effects of settlement, thus if the simplified approach (described in Section 6.1.1 of the Approval in Principle) predicts any significant issues then a more detailed study will be carried out for this part of the structure.

No additional assumptions were required in order to proceed with the assessment. Adequate information was provided by RMS supplemented by the Inspection Report.

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4 Ground Movement Assessment

This section describes the methods of “Greenfield” ground movement calculation, the methods of assessing the ground movement effects on the bridge and gives the results for movements of the structure.

4.1 Method of Ground Movement Calculation

As an initial simple and conservative assessment, the arch and abutments have been modelled in a similar manner to masonry building structures, with ground strains being used to calculate a Risk of Damage Category in accordance with Burland (1995).

In effect, the structure has been simplified to a deep slab/homogenous block which deforms to follow the shape of the settled ground profile. Burland’s guidance has been used to estimate the strain in the structure along the edges and centreline. The centreline has been taken as the axis of the arch barrel.

Burland’s approach considers strains caused by the ‘hogging’ and ‘sagging’ of the building/block as it deforms to follow the ground profile. Bending strain, diagonal strain and horizontal strain are calculated based on the relative settlement and the section properties of the block.

Total bending strain is derived by adding the maximum bending strain and horizontal strain. The critical strain is then taken as the maximum of the total bending strain or diagonal strain and is then compared to the criteria set out in Table 4 to determine the likely level of associated damage due to the ground movement.

This assessment has been carried out using the latest version of the software package XDisp by Oasys which uses the methodology described above [Burland (1995)]:

“XDisp calculates the ground movements induced by tunnelling in terms of three dimensional displacements and horizontal strains. Tunnels are taken as cylindrical excavations in soil. Several methods of solution are available to define the profile of the settlement curves. The equations are based on the normal probability (Guassian) distribution theory. XDisp then uses this to define the settlement profile at the surface or specified depth.

Building damage assessment may be calculated using the Burland (1995) assessment method. Sub-structures are specified by their locations and bending properties and associated with lines of displacement points and a set of damage category tensile strains that define the thresholds of each damage category.”

XDisp’s tunnel analysis method calculates the settlement profile above an excavated tunnel once the user has entered the estimated ground loss.

Sub-surface greenfield ground movements are calculated in this case using empirical methods set out by Mair et al. (1993) and Taylor (1995), where a settlement trough perpendicular to the new tunnel can be estimated using an inverted normal probability curve (Gaussian curve). The three dimensional form of movement is calculated using the Attewell & Woodman (1982) methodology.

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The tunnel advance is described by analogy to a ‘bow wave’ of an advancing ship. In the direction of the tunnel axis this is termed the longitudinal settlement trough, which can be obtained by cumulative normal probability distribution.

Settlement with TBM progress is simulated as discrete tunnel sequence steps as it approaches and passes next to the bridge, based on an estimated TBM progress of 10m/day.

The geometry of the settlement trough perpendicular to the new tunnel is uniquely defined by selecting values for the volume loss and the width of the trough relative to the depth of the tunnel (trough width parameter).

Where it is necessary to estimate ground movements on a plane that is not normal to or parallel to the tunnel axis, equations proposed by Mair et al. (1993 & 1995) are used in XDisp in terms of a G-function obtained from the numerical integration of the normal probability function.

The fundamental parameter that underlies all empirical methods of estimating tunnel settlement is the volume loss, defined as the ratio of the volume of ground movement over the final volume of the tunnel when short term equilibrium has been obtained.

For tunnelling in London Clay, Lambeth Group, Thanet Sand and Chalk and where no geological anomalies such as scour holes have been detected, a volume loss of 1% in accordance with Thames Tunnel’s moderately conservative value has been adopted. The adopted value is conservative when compared with recorded parameters for similar tunnel projects in London. For example experience from Channel Tunnel Rail Link Contract 220 (CTRL), indicates that an average volume loss of 0.5% was achieved for tunnelling with an 8.11m diameter EPB TBM even in soft ground conditions, Wongsaroj et al (2006).

The width of the settlement trough perpendicular to the tunnel is defined in terms of distance ‘i’ in metres from the tunnel centre-line to the point of inflexion on the curve. A ‘k’ value (trough width parameter) provides a relationship between the distance ‘i’ and the depth to the tunnel axis level. Lower values give steeper, narrower troughs whereas higher values give wider, shallower troughs.

A trough width parameter k of 0.5 at ground surface has been used for the assessment. This value is in accordance with Thames Tunnel’s design guidance document.

Trough width parameters can vary as ground displacements will progress upwards through the deposits of the Thanet Sand, Lambeth Group, London Clay and superficial deposits, however the trough width, k is expected to be close to 0.5 at the surface.

The conservativeness of the volume loss proposed for the calculations will accommodate localised variations in the trough width parameter resulting from tunnelling through coarser grained deposits.

Due to the requirement to produce both sub-surface and surface settlement calculations a consistent approach using the Mair et al (1993) method has been adopted. Based on the analysis of field measurements

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of subsurface settlements above tunnels and centrifuge model tests it has been observed that k increases non-linearly with depth. As a result, the k value at any particular elevation is derived from an empirical equation in relation to depth below ground surface and distance from surface to tunnel axis level (Mair et al (1993)).

Estimated ground movements have been derived from XDisp using the methodology described by Burland (1995).

4.1.1 Geotechnical References

Attewell P B and Woodman J P (1982). Predicting the dynamics of ground settlement and its derivatives caused by tunnelling in soil. Ground Engineering, November 1982, 13 - 36.

Mair R. J., Taylor R. N. and Bracegirdle A. (1993). Subsurface settlement profiles above clay in tunnels. Géotechnique 43 No. 2, pp. 315-320.

Taylor R N (1995), Tunnelling in soft ground in the UK. In: Underground. Construction in Soft Ground. K Fujita and O Kusakabe (Eds). Balkema. pp123-126.

Wongsaroj J, Borghi F X, Soga K, Mair R J, Sugiyama T, Hagiwara T and Bowers K H. Effect of TBM driving parameters on ground surface movements: Channel Tunnel Rail Link Contract 220. Geotechnical aspects of underground construction in soft ground, Bakker et al (eds), 2006.

4.2 Ground Conditions

Review of borehole logs at the bridge/tunnel interface has been undertaken in order to confirm the stratigraphy as indicated on Thames Tunnel drawings (refer to the settlement trough in Appendix B). The review determined that the tunnel is located within structured chalk. No geological anomalies were identified during the review.

4.3 Ground Movement Results

The tunnel works will cause some settlement, horizontal movement, and rotation, of the ground beneath the structure. The ground movements have been calculated at each corner of the structure as shown in Figure 3 below in line with the methodology outlined in Section 6.1.1 of the AiP.

Vertical and horizontal ground movements are associated with the settlement trough and have been calculated for foundation depths between 0m and -6m. The values vary minimally between the different foundation depths implying that although the actual foundation depth is unknown this does not create a significant inaccuracy within the results. Refer to Figure 2 and Section 7.2 of the AiP.

Even so, the more onerous values will be used in the assessment. The most onerous ground movement values occur at -6m.

In the permanent condition, the main effect of the tunnelling is a settlement trough, with associated ground curvature and strain. The ground strain

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values have been investigated along the lines across the bridge (blue) as shown in Figure 4.

Calculated ground movements due to tunnelling works at Britannia Bridge are given for locations as per Figure 3 at a foundation depth of -6m. Parallel and Perpendicular are taken in respect to the alignment of the abutments.

Figure 2: Longitudinal Vertical Settlement Profile

Location Vertical settlement / mm

Horizontal Displacement (Parallel) / mm

Horizontal Displacement (Perpendicular) / mm

1 7.0 0.7 1.6

2 8.8 0.4 1.1

3 5.7 0.8 1.7

4 7.8 0.6 1.5

Table 2: Calculated ground movement due to tunnelling works at Britannia Bridge.

N.B. Quoted values are given for locations as per Figure 3 at a foundation depth of -6m. Parallel and Perpendicular are taken in respect to the alignment of the abutments.

0

2

4

6

8

10

12

-200 -150 -100 -50 0 50 100 150

Ve

rtic

al S

ett

lem

en

t, m

m

Longitudinal Distance from Bridge Centreline, m

Bridge Abutment West

Bridge Abutment East

Vertical Displacement at -6m Foundation Level,mm

Vertical Displacement at -4m Foundation Level,mm

Vertical Displacement at Ground Level,mm

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Figure 3: Bridge plan with the location of points used for ground movement calculations.

Figure 4: Bridge plan with the location of directions of ground strain calculations.

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4.3.1 Vertical settlements

Vertical movements at the bridge corners are at their greatest on completion of the tunnel construction. The maximum vertical settlement, occurring at the NW (2) corner of the structure, will be no more than 8.8mm. The maximum differential vertical settlement between the two abutments will be less than 1.3mm and less than 2.1mm along the length of the abutments (i.e. Point 3 to Point 4). Refer to Figure 5 for transient condition movement plots.

Figure 5: Longitudinal Wave Vertical Settlement Profiles at -6m as the TBM progresses close to Britannia Bridge.

0

1

2

3

4

5

6

7

8

9

10

22100 22200 22300 22400 22500 22600

Ve

rtic

al S

ett

lem

en

t, m

m

Tunnel Chainage, m

Point 1

Point 2

Point 3

Point 4

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4.3.2 Horizontal ground movements – Parallel to the bridge abutments

Horizontal movements parallel to the bridge abutments in plan are at their greatest on completion of the tunnel construction. Refer to Figure 6. The absolute horizontal movement parallel to the bridge abutments will be less than 0.8mm.

The maximum differential horizontal movement parallel to the bridge between two abutments will be less than 0.2mm and less than 0.3mm along the length of the abutments (i.e. Point 1 to Point 2).

Figure 6: Longitudinal Wave Parallel Horizontal Displacement at -6m as the TBM progresses close to Britannia Bridge.

-1

-0.8

-0.6

-0.4

-0.2

0

0.2

0.4

0.6

0.8

1

22100 22200 22300 22400 22500 22600

Ho

rizo

nta

l Gro

un

d M

ove

me

nt

Par

alle

l to

Bri

dge

, m

m

Tunnel Chainage, m

Point 1

Point 2

Point 3

Point 4

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4.3.3 Horizontal ground movements – Perpendicular to the bridge abutments

Overall horizontal movements perpendicular to the bridge abutments in plan are at their greatest on completion of the tunnel construction. Refer to Figure 7. The absolute horizontal movement perpendicular to the bridge abutments will be less than 1.7mm.

The maximum differential horizontal movement perpendicular to the bridge between two abutments will be less than 0.4mm and less than 0.5mm along the length of the abutments (i.e. Point 1 to Point 2).

Figure 7: Longitudinal Wave Perpendicular Horizontal Displacement at foundation level as the TBM progresses close to Britannia Bridge.

-0.2

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

22100 22200 22300 22400 22500 22600

Ho

rizo

nta

l Gro

un

d M

ove

me

nt

Pe

rpe

nd

icu

lar

to

Bri

dge

, mm

Tunnel Chainage, m

Point 1

Point 2

Point 3

Point 4

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5 Structural Assessment

5.1 General

A structural assessment has been undertaken for the bridge to determine the effects of tunnelling-induced ground movement on the structure. The structural assessment uses information provided by RMS, in addition to the information gained from the inspection, to assess any impact that may arise due to the induced ground movements. The inspection has verified, as far as possible within the limitations of public access, the current condition of the bridge.

The assessment has determined the differences in load and serviceability effects due to the tunnelling works and does not represent a full assessment of the capacity of the structure. In addition the assessment considered whether monitoring or mitigation works would be required to accommodate the effects of the ground movement.

5.2 Reference Documents

The assessment has been carried out in accordance with the signed Approval-in-Principle, document no. 307-EA-TPI-BR409-000001-AD.

5.3 Structure Records

For the list of information that has been used in the assessment of the Britannia Bridge refer to section 3.2 above.

5.4 Assumptions and Codes used in the Assessment

5.4.1 Assumptions

It should be noted that the following simplifications and assumptions have been made during Britannia Bridge assessment as it is not intended to be a full bridge capacity assessment:

The structure is brick arch with no movement joints.

The section of the arch, where the original part of the brick arch was broken out and replaced with metal plates with brick or concrete backing, is assumed to behave similarly to the rest of the arch. The effects will be assessed in accordance with Burland (1995) methodology similarly to the brick arch.

The reinforced concrete footway extensions are treated as simply supported on rubber bearings as shown on record drawings even though the concrete slab is supported directly on the spandrels adjacent to the abutments.

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5.4.2 List of Codes

BA 16/97 The Assessment of Highway Bridges and Structures. Including amendments 1 and 2.

BA 44/96 Assessment of Concrete Highway Bridges and Structures

BD 21/01 The Assessment of Highway Bridges and Structures.

BD 37/01 Loads for Highway Bridges

BD 44/95 Assessment of Concrete Highway Bridges and Structures

5.5 Structural Assessment Methodology

At the Britannia Bridge, on completion of tunnel construction, the main effect is a settlement trough with associated vertical and horizontal ground movements as well as ground strain.

The structural assessment was undertaken to determine the impact of the ground movement from the tunnelling and is reported below.

5.5.1 Brick arch and substructure

In the permanent condition, the main effect of the tunnelling is a settlement trough, with associated ground curvature and strain. These have been applied to the structure in both longitudinal and transverse directions. It is assumed that the brick arch structure follows the ground profile and therefore the strains in the structure may be estimated based on Burland’s method as described in Section 6.1.1 of the Approval in Principle 307-EA-TPI-BR409-000001 AD.

In the transient condition as the tunnel progresses and ground movements develop around the head of the tunnel, associated ground curvatures and strains also develop. The highest strain is caused by a combination of horizontal ground strain (contours are steepest) and ground curvature (gap between contours). See Figure 8 for the worst strain location in the permanent condition, which is perpendicular to the tunnel, and Figure 9 for the worst strain location in the transient condition which was found by considering lines at varying angles to the tunnel. Strains were also checked along the lines shown in Figure 4 including along the lines of the abutments, and along the arch centreline approximately parallel to the road above.

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Figure 8: Horizontal Displacement Contours around the bridge structure (plan view) in the Permanent Case

Figure 9: Horizontal Displacement Contours around the bridge structure (plan view) in the Transient Case

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The assessment has been based on the highest value of strain found by considering both the transient and permanent condition. The tensile strain of the structure has been calculated in Oasys XDisp based on the following parameters of the masonry model:

Poisson’s Ratio = 0.3

Ratio of Yong’s Modulus to Shear Modulus (E/G) = 2.6

Longitudinal bridge cross section: (W)10.5m x (H)9.3m

West abutment dimensions: (W)25.7m x (H)9.3m

East abutment dimensions: (W)26.5m x (H)9.3m

5.5.2 Reinforced concrete footway extensions

The reinforced concrete footway extensions are simply supported on rubber bearings. They are also partially supported by the arch spandrel walls for lateral stability. Therefore the assessment covers serviceability checks of the rubber bearings and movement joints.

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5.6 Assessment Results

5.6.1 Brick arch and substructure

The tensile strain values quoted are the structure strain values that include bending and shear strain in the structure as well as the ground strain contribution. The XDisp model offers a simplified approach to determining these strains where the structure is represented by a block with dimensions equal to the actual length and height of the structure.

The resulting longitudinal and transverse strains need to be considered together to gain a true understanding of the effects on the structure due to the ground movement.

The results of the assessment are shown in Table 3; the highest tensile strain occurs along the ‘worst case’ line (shown in Figure 6) and is equal to 0.003%. This is very small and hence the level of damage is considered to be negligible in accordance with Table 4 which is extracted from Burland (1995).

Permanent Case Strain (%) Transient Case Strain (%)

1 0.0006 1 0.0011

2 0.0009 2 0.0014

3 0.0012 3 0.0012

4 0.0014 4 0.0014

diagonal 0.0001 diagonal 0.0027

west 0.0003 west 0.0011

east 0.0001 east 0.0009

centre 0.0004 centre 0.0029

worst case 0.0002 worst case 0.0030

Table 3: Britannia Bridge XDisp Output Data

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Figure 10: Longitudinal Wave Maximum Structure Strain as the TBM progresses close to Britannia Bridge (1)

Figure 11: Longitudinal Wave Maximum Structure Strain as the TBM progresses close to Britannia Bridge (2 - Scaled with respect to the limiting tensile strain criteria (0.05%) depicting negligible damage as set out by Burland (1995))

-0.0005

0

0.0005

0.001

0.0015

0.002

0.0025

0.003

0.0035

22100 22200 22300 22400 22500 22600

Max

imu

m T

en

sile

Str

ain

, %

Tunnel Chainage Excavated to, m

Acrossbridge 1

Acrossbridge 2

Acrossbridge 3

Acrossbridge 4

Diagonal

EastAbutment

WestAbutment

BetweenAbutments

"worstcase"

-0.01

0

0.01

0.02

0.03

0.04

0.05

22100 22200 22300 22400 22500 22600

Max

imu

m T

en

sile

Str

ain

, %

Tunnel Chainage Excavated to, m

Acrossbridge 1

Acrossbridge 2

Acrossbridge 3

Acrossbridge 4

Diagonal

EastAbutment

WestAbutment

BetweenAbutments

"worstcase"

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Damage Category

Level of damage

Approx crack width (mm)

Limiting tensile strain (%)

0 Negligible < 0.1 < 0.05 1 Very slight < 1 0.05-0.075 2 Slight < 5 0.075-0.15

3 Moderate 5-15 or a number of cracks > 3

0.15 – 0.3

4 Severe

15-25 but also depends on number of cracks

> 0.3

5 Very severe

Usually > 25 but depends on number of cracks

Table 4: Building/Structure Damage Risk Classification Burland

The metal plates, with concrete or brick backing forming part of the arch soffit where the gas main cast iron duct was cast into the arch structure, are subject to similar strains as provided in Table 3. The damage level will be negligible similar to the brick arch structure.

5.6.2 Reinforced concrete footway extensions and bearings

The reinforced concrete footway extensions are simply supported on rubber bearings. They are also partially supported by the arch spandrel walls for lateral stability. The maximum differential settlement of 1.3mm is small and can be accommodated in the rubber bearings without inducing any additional stresses in the footway structures.

The differential horizontal movement parallel and perpendicular to the bridge abutments is very small at a maximum of 0.3mm and 0.5mm respectively. By inspection the footway rubber bearings will be able to accommodate this small horizontal movement without any adverse effects on the bearing performance.

There are no movement joints at the end of the footway with the backfill resting directly against the ends of the footway structure. The horizontal movement perpendicular to the bridge abutments will therefore result in a small change to the horizontal pressure of the backfill. However this is considered to be negligible and within the range already experienced due to footway thermal movement.

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5.6.3 Movement Capacity

The horizontal movement parallel and perpendicular to the abutments will occur towards the tunnel centreline located to the west of the bridge. Refer to Figure A2 in Appendix A. There are no movement joints anywhere on the bridge. Therefore the differential movement will be accommodated in structure strain and rubber bearings as described in sections 4.6.1 and 4.6.2 above.

5.6.4 Foundations

The ground movements are very small and, by inspection, will have negligible impact on the foundations of the bridge.

Reference should be made to the Inspection Report 307-RI-TPI-BR409-000001-AC for a more detailed description of the condition of the substructure and photographs.

5.6.5 Services

As stated in the AIP, the utilities on the bridge are being assessed and reported separately.

A Data Sheet has been prepared for each utility reporting on utility details, settlement data, and results of the assessment.

The aim of the data sheets is to ensure the project has written consent from each utility company / asset owner that they do not object to the Thames Tunnel project. They also provide a record for further work on the project.

It is expected that written consent will not have been received for each utility prior to submission of this report.

6 Monitoring and Mitigation

6.1 Route-Wide Monitoring

A route-wide Instrumentation and Monitoring Plan has yet to be developed by the Thames Tunnel Project Team. It would include provision for monitoring of vertical and horizontal ground movements, on sections transverse to the centreline of the tunnel, at regular centres. This would monitor the performance of the tunnelling contractor and ensure that ground movements are in line with those predicted by the analysis.

6.2 Asset-Specific Monitoring and Mitigation

The assessment has shown that the effects of tunnelling on Britannia Bridge are very small. Therefore no specific asset mitigation measures are recommended.

The site-wide monitoring outlined above will be adequate to ensure that ground movements are in line with those predicted by the analysis and therefore no asset-specific monitoring is proposed.

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7 Conclusions and Recommendations

Greenfield settlement calculations have been undertaken for the proposed Thames Tunnel using OASYS XDisp analysis. The results of this analysis indicate the following ground movements at Britannia Bridge:

The maximum vertical settlement, occurring at the north west (2) corner of the structure, will be no more than 8.8mm. The maximum differential vertical settlement between the two abutments will be less than 1.3mm and less than 2.1mm along the length of the abutments (i.e. Point 3 to Point 4).

The absolute horizontal movement parallel to the bridge abutments will be less than 0.8mm. The maximum differential horizontal movement parallel to the bridge between two abutments will be less than 0.2mm and less than 0.3mm along the length of the abutments (i.e. Point 1 to Point 2).

The absolute horizontal movement perpendicular to the bridge abutments will be less than 1.7mm. The maximum differential horizontal movement perpendicular to the bridge between two abutments will be less than 0.4mm and less than 0.5mm along the length of the abutments (i.e. Point 1 to Point 2).

A structural assessment of Britannia Bridge has been carried out to assess the impact of the anticipated ground movements on the bridge, based on an inspection from publicly accessible areas and information provided by RMS (A13) plc.

It is considered that the bridge will be able to comfortably accommodate the moderately conservative values of the calculated movements.

Strains induced in the structure are very small and hence the level of damage will be negligible.

Movement effects on the services carried by the bridge are subject to separate assessment and are being reported separately.

Based on the results of this assessment, no asset-specific monitoring is proposed. A route-wide Instrumentation and Monitoring Plan will be developed by the Thames Tunnel Project Team. It will include provision for monitoring of vertical and horizontal ground movements, on sections transverse to the centreline of the tunnel, at regular centres. This will demonstrate that the ground movements at Britannia Bridge are in line with those calculated in the assessment.

8 Further Work

No further inspection or assessment of the Britannia Bridge is required.

A route-wide Instrumentation and Monitoring Plan will be developed by the Thames Tunnel Project Team in order to monitor the performance of the tunnelling contractor and ensure that ground movements are in line with those predicted by the analysis.

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Appendix A – Location Plan and Proposed Tunnel Alignment

The line and level of the tunnel has been taken from the following alignments:

Abbey Mills Route – Provisional Horizontal Alignment for Phase 2 Consultation. CAD File Ref: 100-DO-DES-00000-017402-AL

Abbey Mills Route – Provisional Vertical Alignment for Phase 2 Consultation. CAD File Ref: 100-DO-DES-00000-017423-AI

Figure A1: Location Plan

Figure A2: Proposed Thames Tunnel Alignment at Britannia Bridge

Gas Pipe Bridge over River Lee at Abbey Mills (located to north of road bridge)

Britannia Bridge

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Appendix B – Settlement Trough

Figure B1: Britannia Bridge settlement trough along the centre line of the bridge

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Appendix C – Certificate of Assessment and Checking (Structural)

THAMES TUNNEL

Page 2

Section 2: Check certificate

We certify that reasonable professional skill and care has been used in the preparation of the check of the assessment 307-RG-TPI-BR409-000001 of Britannia Bridge with a view to securing that it has been checked in accordance with the Approval in Principle 307-EA-TPI-BR409-00001-AD dated 07/11/2012 and the appropriate standards listed within it, including any amendments:

Signed: Signed:

Name: Name:

Engineering qualifications:

Name of Organisation:

Date: Date:

Check certificate accepted by asset owner

Signed:

Name: Date:

Position held: Name of Organisation:

Transport for London

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Appendix D – Certificate of Assessment and Checking (Geotechnical)

THAMES TUNNEL

Page 4

Section 2: Check certificate

We certify that reasonable professional skill and care has been used in the check of the greenfield ground settlements 307-RG-TPI-BR409-000001 at Britannia Bridge with a view to securing that it has been checked in accordance with the Conceptual Design Statement 307-RG-TPI-BR000-000001-AD dated 27 September 2011 and the appropriate standards listed within it, including the following amendments:

No amendments.

Signed:

Signed:

Name: Name:

Engineering qualifications:

Name of Organisation:

Date: Date:

Check certificate accepted by asset owner

Signed:

Name: Date:

Position held: Name of Organisation:

Transport for London

307�RI�TPI�BR409�000001 | AB | 30 March 2012

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 UTILITIES LIMITED.

Inspection Report Detailed Bridge Assessments Sub�Package 2C

Transport for London Road Management Services (A13) plc

Britannia Bridge

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Inspection Report Detailed Bridge Assessments Sub�Package 2C Britannia Bridge

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Thames Tunnel

Inspection Report � Britannia Bridge

List of contents

Page number

1 Introduction ...................................................................................................... 5

1.1 Project Description .................................................................................. 5

1.2 Works at Britannia Bridge ........................................................................ 5

1.3 Purpose of this Document ....................................................................... 5

2 Desk Study........................................................................................................ 6

3 Site Inspection Purpose and Methodology .................................................... 6

4 Description of the Structure ............................................................................ 7

4.1 General .................................................................................................... 7

4.2 History ..................................................................................................... 8

5 Access Arrangements for Inspection ............................................................. 8

6 Findings of the Inspection............................................................................... 8

6.1 Superstructure ......................................................................................... 9

6.2 Substructure .......................................................................................... 10

6.3 Foundations ........................................................................................... 10

6.4 Bearing and expansion joints ................................................................. 10

6.5 Parapets ................................................................................................ 10

6.6 Services and Utilities ............................................................................. 10

6.7 Condition Factors for Assessment ......................................................... 11

7 Adjacent Structures ....................................................................................... 11

8 Discussion ...................................................................................................... 12

8.1 Review of Available Data ....................................................................... 12

8.2 Structural Issues .................................................................................... 12

8.3 Finishes ................................................................................................. 13

8.4 Heritage Issues ...................................................................................... 13

8.5 Services and Utilities ............................................................................. 13

9 Conclusions and Recommendations ........................................................... 14

A.1 List of Reviewed Information ................................................................. 15

Appendix B .............................................................................................................. 16

B.1 Photographic Records ........................................................................... 16

Appendix C .............................................................................................................. 26

C.1 General arrangement drawings ............................................................. 26

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List of figures

Page number

Figure 1: Location plan ............................................................................................... 7

Figure 2: Proposed Thames Tunnel alignment ........................................................... 8

Figure 3: Britannia Bridge south elevation with key dimensions ................................. 9

List of photographs

Page number

Photo 1: South elevation .......................................................................................... 16

Photo 2: North elevation ........................................................................................... 16

Photo 3: View on the bridge deck from west............................................................. 17

Photo 4: Brick arch south elevation .......................................................................... 17

Photo 5: South�west abutment elevation .................................................................. 18

Photo 6: Brick arch apex – south elevation .............................................................. 18

Photo 7: R.C. footway slab at south�east abutment .................................................. 19

Photo 8: East abutment ............................................................................................ 19

Photo 9: Iron plates underneath Gas Main ............................................................... 20

Photo 10: North abutment......................................................................................... 20

Photo 11: Brick arch north elevation ......................................................................... 21

Photo 12: North abutment – view on north�west corner ............................................ 21

Photo 13: North abutment – north west corner close up on footway bearing area ... 22

Photo 14: Metal angles supporting brick cladding of R.C. footways ......................... 22

Photo 15: Adjacent structures – utility crossing south of the bridge .......................... 23

Photo 16: Adjacent structures – stairs and brick walls located south�east of the bridge ................................................................................................................. 23

Photo 17: Adjacent structures – brick walls located south�east of the bridge ........... 24

Photo 18: Adjacent structures – brick walls located north�east of the bridge ............ 24

Photo 19: Multiply Service Covers ............................................................................ 25

List of abbreviations

CSO Combined Sewer Overflow

TT Thames Tunnel

PBA Peter Brett Associates

STW Sewage Treatment Works

RMS Road Management Services

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1 Introduction

1.1 Project Description

Thames Water is currently progressing with its planned London Thames Tideway Improvements programme. The improvement works consists of construction of two new tunnels, the Thames Tunnel and the Lee Tunnel, together with a programme of Sewage Treatment Works (STW) upgrades.

Construction of the Thames Tunnel (TT), stretching approximately 23km under the River Thames from West London to East London, is due to commence in 2014. The Tunnel will intercept the flow from the most polluting Combined Sewer Overflows (CSO) of the existing system. The planned alignment runs mainly beneath the River Thames at depths of up to 40m below the river bed in order to minimise the potential impact on third party assets.

The main Thames Tunnel is currently planned to be 7.2m internal diameter with a primary and secondary lining giving an effective 8.5m external diameter with an excavated cut diameter of 8.8m. A number of smaller additional tunnels are required to connect the existing CSOs to the main tunnel.

As part of the works, Thames Tunnel Project Team has appointed Peter Brett Associates (PBA), and their sub�consultant Arup, to carry out the Thames Tunnel Detailed Bridge Assessments for Sub�Package 2C bridges. The Britannia Bridge carrying the A13 across the Limehouse Cut is being assessed within this Sub�Package. The purpose is to demonstrate that the predicted effects from ground movements, induced by the TT works, are within acceptable limits.

1.2 Works at Britannia Bridge

A tunnel is to be constructed west of the Britannia Bridge running northeast between Limehouse and Bromley, at a depth of 55.3m below ground level. The excavated diameter of the tunnel will be 8.8m, internal finished diameter 7.2m. A location plan of the bridge is included in Section 4.1.

1.3 Purpose of this Document

This Inspection Report presents the findings of the desk study and visual and element specific inspection, carried out in order to inform subsequent assessment of the bridge for the effects of ground movements due to tunnel construction. It will discuss the observations made, in both the desk study and inspection, and state recommendations for further work, as appropriate.

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2 Desk Study

A desk study was carried out prior to the site inspection, with the following aims:

a. To gain an understanding of the structural behaviour of the bridge;

b. To review the available information, and determine where additional information might be required in order to carry out the assessment;

c. To prepare for, and plan, the site inspection.

A list of the documents, and other information, that were reviewed during the desk study is provided in Appendix A. Specific findings of the desk study are reported in Section 6.

3 Site Inspection Purpose and Methodology

The site inspection was carried out with the following aims:

a. To gain an understanding of the structural behaviour of Britannia Bridge to supplement that gained from desk study;

b. Where possible, to confirm that the data made available for this structure reflects the current situation;

c. To note any features of the structure that may be particularly affected by settlement due to the construction of the Thames Tunnel;

d. To confirm, wherever possible, the locations of utility services within the bridge or that may be affected by settlement of the bridge itself;

e. And to note any heritage features of the structure.

The inspection was carried out on 20th February 2012 in dry and sunny conditions.

The inspection comprised of a visual inspection of all accessible elements of the bridge, from public areas only. The inspection was carried out from ground level and no intrusive works were undertaken.

The area of investigation was all areas of the bridge that were easily accessible from the areas described above, including footpaths and highway land. The inspection also included observations of any structures immediately adjacent to the bridge which could be affected by settlement of the bridge itself.

A photographic record of the inspection is given in Appendix B.

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4 Description of the Structure

4.1 General

The Britannia Bridge over the A13 is a brick arch bridge of one span carrying the A13 (Commercial Road) over the Limehouse Cut in Limehouse. Refer to Photos 1, 2 and 3 in Appendix B.

The structure is located in the London Borough of Tower Hamlets at Grid Reference TQ 367 811 and a location plan is shown below. The bridge is owned by Transport for London but it is operated and maintained by Road Management Services (RMS) (A13) plc under a 30�year DBFO contract.

The bridge has the following references:

Name: Britannia Bridge

Structure Number: A13/2.90 – Brick Arch Span

A13/2.90/3 – Gas Main Iron Plates

A13/2.90/A – R.C. Footway Extension South

A13/2.90/B – R.C. Footway Extension North

The scope of this report covers the brick arch bridge and the concrete footway extensions. It does not cover the adjacent steel utility bridge, the steel steps, the canal walls, or the retaining walls running parallel to the canal.

Figure 1: Location plan

Britannia Bridge

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Figure 2: Proposed Thames Tunnel alignment

4.2 History

The bridge is part of1850 to span the

In 1870 a cast iron duct was cut into the brick arch and in 1921 the bridge was widened at the north and south ends using a concrete slab and beam construction.

After a principal inspection and assessment in April 1987 a weight restriction was placed on the bridge. Stitching of the lower ring of the brick arch was completed in Decand remove the weight restriction

Between April 1989 and April 1990 the bridge was partially reconstructed involving the replacementnorth and south sideconcrete protection slab over the exiting castdrawings in Appendix C.

5 Access Arrangements for

The structure can be inspected visually from footpaths / towpathsaccess provisions will have to be arranged including working from water and at height. Further

6 Findings of the Inspection

The bridge carries the A13 dual carriageway over the Limehouse Cut. The carriageway and footway surfacing are in good condition.

The brick arch structure is generally in fair condition wiseepage and localised repairs. The reinforced concrete footways are in good condition.

Proposed Thames Tunnel

Proposed Thames Tunnel alignment

is part of the A13 Commercial Road and was original1850 to span the Limehouse Cut.

In 1870 a cast iron duct was cut into the brick arch and in 1921 the bridge was widened at the north and south ends using a concrete slab and beam

inspection and assessment in April 1987 a weight was placed on the bridge. Stitching of the lower ring of the brick

arch was completed in December 1987 to strengthen the existing bridgeweight restriction.

Between April 1989 and April 1990 the bridge was partially reconstructed placement of the concrete footpath extensions

north and south sides of the bridge and construction of new reinforced concrete protection slab over the exiting cast�iron gas main ductdrawings in Appendix C.

Arrangements for Inspection

The structure can be inspected visually from the surrounding roads and towpaths. To carry out a more detailed inspection

provisions will have to be arranged including working from water Further inspection is not proposed at this stage.

Findings of the Inspection


The brick arch structure is generally in fair condition with signs of water seepage and localised repairs. The reinforced concrete footways are in

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originally built in

In 1870 a cast iron duct was cut into the brick arch and in 1921 the bridge was widened at the north and south ends using a concrete slab and beam

inspection and assessment in April 1987 a weight was placed on the bridge. Stitching of the lower ring of the brick

1987 to strengthen the existing bridge

Between April 1989 and April 1990 the bridge was partially reconstructed of the concrete footpath extensions on both

and construction of new reinforced iron gas main duct. Refer to

surrounding roads and To carry out a more detailed inspection special

provisions will have to be arranged including working from water inspection is not proposed at this stage.


th signs of water seepage and localised repairs. The reinforced concrete footways are in

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The Limehouse Cut towpath surfacing is in good condition as is the visible part of the canal wall supporting the towpath.

6.1 Superstructure

The bridge consists of a skewed brick arch. The clear square span between east and west abutment at the arch springing level is 9.1m. Refer to Figure 1 below. The total width of the brick arch measured along the face of the east abutment is 22m. There are large metal plates in the soffit of the arch on the north side of the bridge where the gas main cast iron duct was cut into the arch structure. The cast iron duct is protected from the top by a reinforced concrete slab supported by the brick arch on either side of the opening. Refer to Photo 9 and drawings in Appendix C.

Each side of the bridge has been widened with reinforced concrete extensions spanning approximately 16m between east and west abutments and partially supported by the brick spandrels and arch barrel.

Figure 3: Britannia Bridge south elevation with key dimensions

6.1.1 Brick arch:

The arch ring was generally in a fair condition with no signs of any distortion to the barrel or any major defects. During site inspection weathering, spalling and staining were noted as well as areas of green algae where seepage has occurred through the brickwork. Refer to Photos 8, 10 & 12. The visible surface of the metal plates embedded in the crown of the arch are in good condition with only minor sign of corrosion on the edges. Refer to Photo 9.

There are patches where original blue brick have been replaced with different colours of brick (yellow and red). The most extensive area of replacement, including recent mortar repairs, occurs on the north end of the barrel and around the iron plates. Refer to Photos 9 and 10.

Minor damage to the edge of the arch ring was noted at several locations, likely to be accident damage due to the movement of canal traffic below. More significant damage was repaired with mortar which is in good condition. Refer to Photos 5, 6 and 11.

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6.1.2 Spandrels:

The original spandrel walls are mostly obscured by recent reinforced concrete footway extensions built to the north and south of the arch. The visible part of the spandrel walls was in fair condition with signs of water seepage in the corners and below the footway extensions. Refer to Photos 5, 7 and 12

6.1.3 Reinforced concrete footway extensions:

The visible parts of the footway extension structures are in good condition with no signs of cracking or water seepage. Steel angles supporting brick cladding on the external side of the bridge show signs of corrosion. Refer to Photo 14.

6.2 Substructure

The arch abutments were generally in a fair condition with no signs of any major defects. During site inspection weathering, spalling and staining were noted as well as areas of green algae where seepage has occurred through the brickwork. Active water ingress was noted at one location on the east abutment, approximately three meters from the southern end of the arch. This was causing a slight water build up on the tow path. Refer to Photo 8. Since the water ingress is in a localised area it is likely that it is due to a leaking water main or sewer located within the road above

6.3 Foundations

There are no details available on the extent of the foundations but there is no evidence of settlement or other foundation problems which would give concern regarding their condition or performance.

6.4 Bearing and expansion joints

There are no expansion joints on the bridge.

The reinforced concrete footway extensions are supported on rubber bearings as shown on record drawings even though the concrete slab is supported directly on the spandrels adjacent to the abutments. Dislocated bricks were noted in a curtain wall on the north�west bearing shelf. Refer to Photo 13.

6.5 Parapets

The external parapets are steel with mesh infill. Steel posts are bolted to the reinforced concrete bridge footway extensions. Adjacent to the parapet is a pedestrian footway with a steel railing separating the footway from the road. Both parapets and railing were in good condition.

6.6 Services and Utilities

Information has been received from utility owners indicating British Telecom, Cable and Wireless, COLT, Geo Networks, Fibrenet, Interoute, Level 3 Communications, RMS, TFL, Verizon and Virgin Media services running along the highway corridor and indicated by the presence of

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multiple covers and cabinets (Refer to Photo 19), but all of these are considered as being relatively flexible cables.

Further information received indicates a Scottish and Southern Energy fibre optic duct (to be confirmed) on the west side of the bridge.

Received record drawings, dated 1989, indicate the presence of the following utilities in the bridge in addition to those listed above:

A) North side of the bridge:

• National Grid Gas 48 inch cast iron medium pressure gas main reducing into several 18 inch diameter pipes to cross the bridge in the cast iron duct cut into the arch structure,

• National Grid Gas 450mm gas main running in the north footway extension,

• Thames Water 450mm water main running in the north footway extension

B) South side of the bridge:

• National Grid Gas two 18 inch gas mains in the south footway extension. Information from NGG indicates that these have been replaced with one 450mm diameter steel main.

• A Thames Water 15 inch water main crosses the bridge on the south side. The pipe diameter increases to a 20 inch pipe once off the bridge behind the east abutment. There is an additional 8 inch pipe connecting to this water main at the location of diameter change. The pipe is connected at right angles to the main and runs south behind the east bridge abutment. The pipe tee connection is located in the area where active leakage has been noted. Refer to section 6.2 above.

Due to the inspection being limited to public areas only it was not possible to inspect the services housed within the steel utility bridge (refer to Photo 15).

6.7 Condition Factors for Assessment

The visible parts of the arch structure are in fair condition. A Condition Factor of 0.8 would be used in further assessment.

The visible parts of the reinforced concrete footway extensions are in good condition. A Condition Factor of 1.0 would be used in further assessment.

7 Adjacent Structures

The scope of this report covers the brick arch bridge and the concrete footway extensions. It does not cover the adjacent steel utility bridge, the steel steps, the canal walls, or the retaining walls running parallel to the canal as described below.

There are brick retaining walls in line with the west and east abutments extending along the Limehouse Cut to north and south of the bridge. It is

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understood, following discussion with RMS, that these are owned by adjacent landowners.

The front wall on the south�east corner of the bridge supports the steel stairs leading from Limehouse Cut towpath up to Commercial Road. The back wall positioned at the back of the stairs supports buildings above. The space between walls and below the steel stairs is possibly used as a utility chamber. Refer to Photo 1.

The wall on the north�east corner of the bridge supports the brick parapet above.

The wall on the south�west and north�west corners of the bridge is set back further from the bridge west abutment face and supports the footway at the street level.

The walls were in fair condition, showing signs of weathering, spalling with some localised mortar loss. The cracking and movement of the wall to the north east of the structure as noted in the 2006 Principal Inspection Report has not been repaired and is therefore classed as poor condition. Refer to Photos 16, 17 and 18.

There is a steel utility bridge located immediately south of the Britannia Bridge. Refer to Photo 15. At present it is not clear what services are being carried by this structure. The bridge is most likely to carry 450mm diameter steel gas main diverted from the south side of the bridge during construction of footways in 1990. The structure is in good condition.

8 Discussion

8.1 Review of Available Data

Currently no drawings are available for the brick arch structure spanning the Limehouse cut. Some limited dimensional data is provided in previous inspection reports and has been verified during the visual inspection. The original construction drawings provide the majority of structural data on the reinforced concrete footway extensions.

The inspection confirmed that the Principal Inspection Report 2006, reflects the current arrangement and condition of Britannia Bridge.

As discussed in more detail below, it will be possible to undertake a simplified assessment of the bridge with the existing data but it is recommended that additional information be obtained regarding the dimensions and materials of the structure if any detailed assessment is required.

8.2 Structural Issues

The structure is to be assessed for the effects of ground movements due to the proposed construction of the Thames Tunnel. Refer to Section 1.2.

Strains will be induced in the structure by differential movement of the ground causing differential vertical or horizontal effects in the structure. Ground strains will also occur along the line of the abutments. To assess these effects the arch and abutments will be modelled in a similar manner

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to masonry building structures, with ground strains being used to calculate Risk of Damage Category in accordance with Burland (1995).

8.3 Finishes

There are no particularly sensitive finishes to the structure that could be adversely affected by movements of the foundations.

8.4 Heritage Issues

The Britannia Bridge is not a listed structure.

8.5 Services and Utilities

Information received identified multiple communication services crossing the bridge which comprise solely of flexible fibre optic cabling and ducts, it is anticipated that ground movements will have minimal effect on these.

Further information is required on the Scottish and Southern Energy fibre optic duct regarding the type and condition of the cable to be able to assess the likely effects due to ground movements.

In addition further information is required on the construction and condition of the National Grid Gas and Thames Water utilities as listed in section 6.6 above.

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9 Conclusions and Recommendations

The visual and element specific inspection was carried out on 20th February 2012 and the data from the inspection was collated with that from desk studies. The following conclusions were reached:

• The available information broadly reflects the current arrangement and condition of the structure. No discrepancies in the available information were noted.

• A condition factor of 0.8 for assessment of the arch spans and 1.0 for assessment of the reinforced concrete footways will be adopted, if required.

• There are no finishes, or structural details, that are particularly sensitive to the effects of foundation movements.

• There are no heritage features of concern.

• Additional information is required about the type, condition and pipe construction for the fibre optic cable, water pipes and multiple gas pipes to be able to assess the likely effects due to ground movements.

• Active water ingress was noted at one location on the east abutment. Refer to section 6.2. This was also noted in the WSP Principal Inspection Report from February 2006.

• The cracking and movement of the wall to the north east of the structure as noted in the WSP Principal Inspection Report from February 2006 has not been repaired.

Calculations are being carried out as part of the Thames Tunnel Detailed Bridge Assessments, to determine the anticipated settlements at Britannia Bridge over Limehouse Cut. Adequate information is available to carry out the assessment of the effects on the bridge

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A.1 List of Reviewed Information

Drawings:

Drawing Number Title

53514 / TE / 01 / 9240 General Arrangement

53514 / TE / 01 / 9241 Site Clearance

53514 / TE / 01 / 9242 Setting Out

53514 / TE / 01 / 9243 Civil Works

53514 / TE / 01 / 9244 Civil Works Details; Sheet 1

53514 / TE / 01 / 9245 Civil Works Details; Sheet 2

53514 / TE / 01 / 9246 Road Marking and Signing

53514 / TE / 01 / 9247 Statutory Authorities Services

53514 / TE / 01 / 9248 Temporary Diversions; With Footbridge (Provisional)

53514 / TE / 01 / 9249 Temporary Diversions; Without Footbridge

53514 / TE / 01 / 9260 General Arrangement of Slab over Gas Main

53514 / TE / 01 / 9261 R.C. Details of Slab Over Gas Main

53514 / TE / 01 / 9270 G.A. of Replacement Footway and Parapets

53514 / TE / 01 / 9271 Setting Out of Northern Parapet and Footway

53514 / TE / 01 / 9272 Setting Out of Southern Parapet and Footway

53514 / TE / 01 / 9273 Northern Parapet and Footway Reinforcement Details

53514 / TE / 01 / 9274 Southern Parapet and Footway Reinforcement Details

Reports:

Document Number Issue Date Title

A13 / TH / EXR / 06/ 906 17/03/1992 Britannia Bridge No A13/2.90; Principal Inspection

A13 / TH / EXR / 06/ 914 26/02/1992 Approval in Principle for the Assessment of the Brick Arch only of Britannia Bridge No A13/2.90

A13 / TH / EXR / 06/ 919 18/03/1994 Defect Assessment – Service Ducts

A13 / TH / EXR / 06/ 920 18/03/1994 Defect Assessment – Piers, Concrete Slab, Drainage, Waterproofing and Parapets

A13 / TH / EXR / 06/ 921 18/03/1994 Defect Assessment – Bearings, Expansion Joints

A13 / TH / EXR / 06/ 922 18/03/1994 Inverts or Aprons, Abutments, Arch Ring, Spandrels, Surfacing, Walkways

99C011 / 1 / A 16/03/1999 Principal Inspection Report

10401280 / A13�2.90 02/2006 Principal Inspection Report

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Appendix B

B.1 Photographic Records

Photo 1: South elevation

Photo 2: North elevation

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Photo 3: View on the bridge deck from west

Photo 4: Brick arch south elevation

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Photo 5: South�west abutment elevation

Photo 6: Brick arch apex – south elevation

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Photo 7: R.C. footway slab at south�east abutment

Photo 8: East abutment

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Photo 9: Iron plates underneath Gas Main

Photo 10: North abutment

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Photo 11: Brick arch north elevation

Photo 12: North abutment – view on north�west corner

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Photo 13: North abutment – north west corner close up on footway bearing area

Photo 14: Metal angles supporting brick cladding of R.C. footways

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Photo 15: Adjacent structures – utility crossing south of the bridge

Photo 16: Adjacent structures – stairs and brick walls located south�east of the bridge

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Photo 17: Adjacent structures – brick walls located south�east of the bridge

Photo 18: Adjacent structures – brick walls located north�east of the bridge

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Photo 19: Multiply Service Covers

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Appendix C

C.1 General arrangement drawings

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Copyright notice Copyright © Thames Water Utilities Limited September 2013. All rights reserved. Any plans, drawings, designs and materials (materials) submitted by Thames Water Utilities Limited (Thames Water) as part of this application for Development Consent to the Planning Inspectorate are protected by copyright. You may only use this material (including making copies of it) in order to (a) inspect those plans, drawings, designs and materials at a more convenient time or place; or (b) to facilitate the exercise of a right to participate in the pre-examination or examination stages of the application which is available under the Planning Act 2008 and related regulations. Use for any other purpose is prohibited and further copies must not be made without the prior written consent of Thames Water. Thames Water Utilities LimitedClearwater Court, Vastern Road, Reading RG1 8DB The Thames Water logo and Thames Tideway Tunnel logo are © Thames Water Utilities Limited. All rights reserved.

Copyright notice Copyright © Thames Water Utilities Limited September 2013. All rights reserved. Any plans, drawings, designs and materials (materials) submitted by Thames Water Utilities Limited (Thames Water) as part of this application for Development Consent to the Planning Inspectorate are protected by copyright. You may only use this material (including making copies of it) in order to (a) inspect those plans, drawings, designs and materials at a more convenient time or place; or (b) to facilitate the exercise of a right to participate in the pre-examination or examination stages of the application which is available under the Planning Act 2008 and related regulations. Use for any other purpose is prohibited and further copies must not be made without the prior written consent of Thames Water. Thames Water Utilities LimitedClearwater Court, Vastern Road, Reading RG1 8DB The Thames Water logo and Thames Tideway Tunnel logo are © Thames Water Utilities Limited. All rights reserved.

10243-A4P-Copyright-imp-V01.pdf p1 12:03:39 September 21, 2013

Application Reference Number: WWO10001 Tunnel and Bridge Assessments · 2016-05-05 · Tunnel and...

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