Application Reference Number: WWO10001 Tunnel and Bridge … · 2016-05-05 · improvement works consist of construction of two new tunnels, the Thames Tunnel and the Lee Tunnel,

Tunnel and Bridge AssessmentsCentral ZoneCable & Wireless Tower Subway CrossingDoc Ref: 9.15.31

Folder 97 September 2013DCO-DT-000-ZZZZZ-091500

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Thames Tideway Tunnel Thames Water Utilities Limited

Application for Development ConsentApplication Reference Number: WWO10001

Cable and Wireless – Tower Subway

Detailed Assessment of Ground Movement Effects on Cable and Wireless Tower Subway

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Thames Tunnel

Cable & Wireless Tower Subway Crossing

List of contents

Page number

1 Executive summary ......................................................................................................... 4

2 Description of works ....................................................................................................... 5

2.1 Site description ...................................................................................................... 5

2.2 Asset descriptions ................................................................................................. 5

2.3 Proposed Thames Tunnel works ........................................................................... 6

2.4 Ground conditions ................................................................................................. 7

3 Ground movement assessments ..................................................................................... 9

3.1 General .................................................................................................................. 9

3.2 Analytical method ................................................................................................. 9

3.3 Assessment assumptions ....................................................................................... 9

3.4 Ground movement estimates for structural assessment ...................................... 10

4 Structural assessment ................................................................................................... 13

4.1 General ................................................................................................................ 13

4.2 Cast iron lining details ........................................................................................ 13

4.3 Analytical method ............................................................................................... 14

5 Conclusion ..................................................................................................................... 21

References ............................................................................................................................... 22

Appendix A – Calculations ................................................................................................. Appendix B – Drawings ..................................................................................................... Appendix C – Risk Register ............................................................................................... Appendix D – Inspection Report ........................................................................................



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1 Executive summary Thames Water is currently progressing with its planned Tideway improvements. The improvement works consist of construction of two new tunnels, the Thames Tunnel and the Lee Tunnel, together with a programme of sewer upgrades. The Thames Tunnel (TT) comprises of construction of an 8.1m – 8.8m excavated diameter tunnel, stretching approximately 23km for much of its route under the River Thames from West London to Abbey Mills is due to commence in 2016.

This report assesses the likely ground movements that may arise from construction of the Thames Tunnel works and the impacts on the Tower Subway Tunnel currently owned by Cable & Wireless. The interface is located in the middle of the River Thames to the west of Tower Bridge. The Thames Tunnel will have an excavated diameter of 8.8m at this location and will be constructed at a clear distance of 26.5m below the Cable and Wireless Tower Subway tunnel. The part of the Tower Subway tunnel which is subject to ground movement due to the Thames Tunnel works, is a 2.134m (7 feet) internal diameter cast iron segmentally lined tunnel carrying fibre optic cables and redundant water mains. The assessment has been based on a number of assumptions regarding the tunnel lining material and properties. Additional information of the tunnel lining geometry was obtained during a tunnel inspection undertaken on the 4th November 2011. The inspection report is included in Appendix D. The inspection confirms earlier observations which were recorded as part of an inspection undertaken by Arup in March 2010 for the More London Development on the south bank. Even though the tunnel lining exhibits a high degree of corrosion in some areas, particularly at crown level, with some pitting of the pans, flanges and bolts, it is considered that the corrosion is mainly superficial with only minimal loss of structural section and the structural capacity. However, the impact of corrosion has been considered in the assessment and a condition factor of 0.9 is adopted in accordance with LUL standard G-055 and 1-055. Using conservative estimates of the ground movements that may arise from construction of the Thames Tunnel, the impact on the Tower Subway tunnel has been appraised. The calculations indicate that the tunnel will settle by a maximum of 14.5mm and be subjected to an imposed radius of curvature of approximately 19.6km. The calculated movements will impose longitudinal and radial distortions on to the tunnel lining. The radial deformations have been assessed using standardised methods and the resulting bending moments and hoop thrusts have been appraised to be within acceptable limits. Checks on the lining and bolt stresses caused by the imposed longitudinal distortions have also been assessed to be within acceptable limits.

The maximum expected gap between segments due to bending together with the maximum imposed gap due to horizontal displacement has been calculated to be 0.17mm. Since the Tower Subway tunnel is founded in the relatively impermeable London Clay, it is not anticipated that opening up of these joints will result in a significant change in the amount of water ingress that is currently taking place into the tunnel.



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2 Description of works

2.1 Site description 2.1.1 Site location

The proposed Thames Tunnel and Tower Subway interface is located in the middle of the River Thames between Tower Hill on the north bank of the Thames, and Vine Lane (off Tooley Street) on the south bank.

From drawing no. 100-DA-TPI-TU014-810001 RevAA the river bed level at the crossing between the two tunnels is at 91.5m ATD (ATD = Above tunnel datum: 100mATD = 0m Ordnance Datum). The depth from river bed level to the axis of the Thames Tunnel is 39.1m and the minimum vertical clearance between the crown of the Thames Tunnel and the invert of the Tower Subway tunnel is 26.5m. The site location and position of the Tower Subway tunnel is shown in Drawing 100-DA-TPI-TU014-810000 RevAB.

2.2 Asset descriptions The Tower Subway tunnel was constructed in 1869 using a wrought iron “Barlow-Greathead shield”. It was originally conceived to carry passengers on a short railway, but was later converted to be a pedestrian tunnel. It was closed to pedestrians in 1898 and subsequently used to carry pipes for the London Hydraulic Power Company. It is now owned and operated by Cable and Wireless and carries fibre optic cables and redundant water mains. It has an internal diameter of 2.134m.

Information about the asset has been obtained from archive drawings, Thames Tunnel alignment drawings received from the Thames Tunnel project team and from a visual inspection undertaken on the 4th November 2011. The information is summarised below in Table 1.

Additionally, the following paper gives some information on the original tunnel construction and lining, along with details of repairs that were made to the northern part of the tunnel following air-raid damage during the Second World War:

• “Emergency Repair to the Tower Subway, London, after Air-raid damage”. H J B Harding, Journal of the ICE, Volume 25, Issue 1, pages 73 –79, 1945.

This paper states that the lining is cast iron, comprising three segments plus a key.

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Table 1: Asset information

Classification Description Asset name Tower Subway Asset owner Cable and Wireless Built 1869 Dimensions 2.134m internal diameter (in area effected by

ground movement) Type Cast iron – 3 segments plus key. Flange depth

= 50mm (measured) Ring length = 910mm (measured).

River bed level 91.5m ATD Invert level 83.3m ATD Available/received surveys Condition survey of part of tunnel carried out

by Arup in March 2010 Condition survey of part of tunnel carried out by Arup in November 2011 as part of the Thames Tunnel project

The material properties of the lining cannot be determined by the available information and hence properties based on LUL standards have been adopted for the assessment. However, the dimensions of the segments were confirmed during the tunnel inspection and this is reflected in the assessment.

2.3 Proposed Thames Tunnel works 2.3.1 Construction programme

A detailed construction programme for the bored tunnel is yet to be confirmed, however, it is understood that construction work is due to start in 2016. According to the current programme tunnelling will cross beneath the Tower subway in summer / autumn 2019. 2.3.2 Thames Tunnel

The main Thames Tunnel is currently planned to be 7.2m internal diameter with a primary and secondary lining giving an effective 8.5.m external diameter and an excavated cut diameter of 8.8m. The Thames Tunnel in this location is anticipated to be constructed using an Earth Pressure Balance (EPB) style Tunnel Boring Machine (TBM), using a precast segmental lining. The tunnel crown (measured for the excavated diameter) is at approximately 56.8m ATD and the TBM is anticipated to encounter both the Lambeth Group and the Thanet Sand strata at the crossing position of the Tower Subway. The planned alignment for the Thames Tunnel runs mainly beneath the River Thames. At the interface with the Tower Subway tunnel, the Thames Tunnel (axis level) is located 39.1m below the river bed.



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2.4 Ground conditions A review of available borehole logs has been undertaken in order to establish ground conditions at the Thames Tunnel interface. The review has also appraised whether geological features such as scour hollows are likely to be present that may affect the tunnel construction. It is important to establish whether geological anomalies are present since it can impact on tunnelling construction and the likely ground movements. The geological sequence at the proposed Thames Tunnel / Tower Subway area is based primarily on borehole SR2038, completed in January 2010 by Fugro as part of the “Thames Tunnel – Phase 2: Over-water boreholes” programme of ground investigation. The following boreholes have also been reviewed:

• TQ38SW1586 • TQ38SW2863 • TQ38SW3392

A summary of the borehole logs indicate that the geological sequence in the surrounding area comprises Made Ground, River Terrace Deposits, London Clay Formation, Harwich formation, Lambeth Group Formation, Thanet Sand Formation and Seaford Chalk Formation. The Tower Subway tunnel, with a crown level at 85.4m ATD and an invert level at 83.3m ATD, is entirely located within the London Clay stratum. The Thames Tunnel, with an axis level at approximately 54.2m ATD lies at the interface between the Lambeth Group and the Thanet Sand strata and is in agreement with Thames Tunnel’s Ground Model. The boreholes show no indications of geological anomalies such as gravel infilled deposits extending in to the London Clay. The stratigraphy above the tunnel crossing is summarised in Table 2.



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Table 2: Summary of ground conditions

Geological formation and stratigraphy Approximate level of top of

stratum (mATD)

Quaternary River Terrace Deposits 91.9 Palaeogene Eocene Thames

Group London Clay Formation

90.9

Harwich Formation

72.1

Palaeocene Lambeth Group

Reading Formation

Upper Mottled Beds

71.9

Woolwich Formation

Laminated beds

65.1

Reading Formation

Lower Mottled Beds

62.1

Upnor Formation

55.4

Thanet Sand Formation 54.6 Bullhead Beds 41.6

Cretaceous White Chalk Subgroup Seaford

Chalk Formation

White Chalk Subgroup

41.5



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3 Ground movement assessments

3.1 General The ground movement assessment of the Tower Subway tunnel has considered transitory and end of construction displacements that may be caused by construction of the Thames Tunnel. The magnitude and distribution of these ground movements are a function of many factors such as geotechnical properties of the ground, construction sequence and program, and the overall standard of workmanship. The assessment of ground movement assumes that a ‘high standard of workmanship’ is adopted by the Contractor. This is assured by review and approval by all relevant parties of the contractors’ method statements. Nonetheless, a conservative approach has been adopted in the selection of input parameters, with the result that this assessment represents a ‘moderately conservative’ estimate of ground movement effects.

3.2 Analytical method Sub-surface Greenfield ground movements are calculated using empirical methods; 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. Unless otherwise stated ground movements discussed in this report represent “Greenfield” values – that is, it is assumed that overlying or adjacent structures have no influence on the magnitude or distribution of the estimated movements at foundation level. This is a conservative, simplifying assumption and the stiffness of individual structures and their depth of embedment may reduce structural deformations. The estimated ground movements at the asset location are derived using Arup’s in-house verified Excel spreadsheet and checked against displacements derived from the OASYS software XDISP.

3.3 Assessment assumptions The borehole review, described in Section 2.4, confirms that the Tower Subway tunnel is located within the London Clay stratum, with the Thames Tunnel located at the interface of the Lambeth Group and the Thanet Sand. Since there is no evidence from the borehole review that scour hollows or other geological anomalies are present, the “moderately conservative” volume loss parameter as specified by the Thames Tunnel project team are deemed appropriate for the ground movement assessment. 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 in similar ground conditions, Wongsaroj et al, 2006.

Table 3: Assessment parameters

Assessment parameters Value Volume Loss

1.0%

Trough width parameter (K) Derived using the Mair et al (1993) method



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3.4 Ground movement estimates for structural assessment In order to determine the imposed deformation of the Tower Subway tunnel for the structural assessment in Section 4, ‘Greenfield’ vertical ground movements have been calculated along the tunnel at levels corresponding to the crown and invert. These levels are intrados positions of the tunnel. The estimated settlement along the Tower Subway tunnel is presented graphically in Figure 1.

Figure 1: Tunnel crown and invert vertical movement

The estimated ground movements have been used to assess the following tunnel deformations, assuming the tunnel moves freely with the ground:

• Maximum tunnel squat/elongation in the transverse direction; and • Worst case radius of curvature imposed on the tunnel in the hogging and sagging

zones in the longitudinal direction. 3.4.1 Maximum tunnel squat/elongation

The diametrical distortion, i.e. the change in diameter divided by the original tunnel diameter, of a tunnel lining due to ground loading will result in either an increase of the vertical diameter and a decrease of the horizontal diameter (elongation) or an increase of the horizontal diameter and a decrease of the vertical diameter (squat). The maximum vertical displacement at levels corresponding to the tunnel crown and invert are summarised in Table 4. The distortion of the Tower Subway tunnel is calculated by

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dividing the maximum differential ground movement (i.e. the difference between crown and invert settlement) by the diameter of the tunnel.

Table 4: Calculated distortion

Maximum vertical displacement Invert

Crown Max. differential Diametrical

distortion Sagging

zone 14.5mm 14.0mm

0.5mm 0.023%

Hogging zone

2.9mm 3.1mm 0.2mm 0.010%

The effect of elongation/squat will result in a potential increase in bending moment of the segmental lining that may cause rotation of the joints. The calculated value forms part of the structural assessment (see Section 4.3.1). 3.4.2 Tunnel imposed radius of curvature

The critical mode of longitudinal deformation is where the tunnel deforms (bends) within a sagging or a hogging zone. The radius of curvature has been calculated considering incremental radii of curvature between the points of inflection. The tightest imposed radius of curvature, R’imposed has been calculated as the minimum of these values, as illustrated in Figure 2 below.

Figure 2: Imposed radius of curvature

L is the cumulative distance between the incremental intervals and δ is the magnitude of displacement between the points. For the Tower Subway tunnel, the sagging zone is the most critical zone and the vertical movements are used to calculate the worst case imposed radius of curvature. This is summarised in Table 5 below.



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Table 5: Calculated imposed radius of curvature

Minimum imposed radius of curvature, R’imposed due to vertical movement Sagging

Tower Subway Tunnel 19.6km The radius of curvature will be used to assess the structural impact on the Tower Subway tunnel in the longitudinal direction (see Section 4.3.6 and 4.3.7). This will include assessing the size of the gap which may open up between two segments.



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4 Structural assessment

4.1 General The cast iron lining assessment method considers the change in stresses from the existing condition prior to the construction of the Thames Tunnel.

4.2 Cast iron lining details The following table summarises the cast iron lining geometry based on available information and measurements taken during the visual inspection. Assumed values are highlighted and annotated below.

Table 6: Cast Iron Lining Geometry

Dimension/property Value Notes Internal diameter 2.134m (7 ft) 1 No. of segments 3 plus key 1 Ring length 910mm (measured) 1 Ring width 448mm (measured) Flange depth 50mm (measured) 1 Flange thickness 24mm (measured) 1 Central rib (longitudinal) depth 50mm (measured) 1 Central rib (longitudinal) thickness

24mm (measured) 1

Plate/skin thickness Approximately 30mm (measured) 1 Cast iron Young’s Modulus 100,000MPa ± 12.5% 2 Cast iron compressive strength 150 N/mm² 2 Cast iron tensile strength 38 N/mm² 2 Number of radial bolts 6

(5 observed, 6 expected) 1

Young’s Modulus - bolts 190N/mm2 2 Ultimate tensile strength - bolts 342N/mm2 2 Number of circumferential bolts 19

(13 observed, 19 expected) 1

Condition factor (to account for corrosion)

0.9 2

Bolt length 115mm (measured) 1 Bolt diameter 19.05mm (¾ in) 1 Size of bolt hole 25.4mm (1 in) 2 Notes:

1 Visual inspection carried out on the 4th November 2011 as part of the Thames Tunnel project.

2 Segment properties based on LUL standards for cast iron lined tunnels.



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4.3 Analytical method 4.3.1 Change in lining stresses due to squat/elongation of tunnel section

An outline of the assessment procedure is presented below in Figure 3. Calculations are included in Appendix A.

Figure 3: Assessment procedure – transverse direction

4.3.2 Permissible tunnel lining capacity envelope

The lining capacity envelope is determined by plotting an interaction diagram. The interaction diagram can be plotted, by computing the bending moment and hoop force values. This provides an envelope which defines the limit of the cast iron lining capacity. Lining dimensions and cast iron grade are parameters that impact on the capacity envelope. The interaction diagram for the Tower Subway tunnel is based on the parameters summarised in Section 4.2. 4.3.3 Determine existing lining stresses

The existing stresses, which do not include the effect of the Thames Tunnel, are calculated using Duddeck and Erdmann (1985). Tunnel stresses using Duddeck and Erdmann are assumed to be in a continuous elastic environment and therefore, it does not take in to account any volume lost or relaxation of the ground. However, the number of assumptions made in this report, collectively produce a conservative assessment of the stresses in the tunnel lining.

PERMISSIBLE TUNNEL LINING CAPACITY ENVELOPE

From lining material and section properties

DETERMINE EXISTING HOOP FORCES IN LINING

Using Elastic Continuum method after Duddeck

and Erdmann (1985)

DETERMINE CHANGE IN BENDING MOMENT IN LINING DUE TO THAMES

TUNNEL CONSTRUCTION

Apply calculated distortion to tunnel and use Morgan (1961) method to calculate change in

BM

CHECK THE AXIAL FORCE/BENDING MOMENT REMAINS WITHIN THE

PERMISSIBLE CAPACITY ENVELOPE



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The existing stresses are calculated in accordance with a number of assumed parameters. These are presented in Table 7.

Table 7: Assumed key parameters

Assumed key parameters Earth pressure coefficient at tunnel location K0=0.7 Young’s modulus of cast iron E = 112.5GPa (100GPa+12.5%) Surface surcharge No surcharge as tunnel interface is located in

the middle of River Thames Existing diametric distortion of the tunnel See below

Ko is dependent upon the groundwater pressure profile, Mayne & Kulhawy (1982), and previous loading that the soil at tunnel level is subjected to. Estimates based on past previous loading from geological records and the removal of overburden across London indicates that following tunnel construction the horizontal stress will drop relative to the vertical stress and K0 will therefore be less than 1.

Changes in horizontal stress and a reduction of K0 following tunnel construction are likely to have resulted in the Tower Subway tunnel having a “squatted” tunnel profile. As no dimensional survey records have been obtained at the time of the assessment, the existing distortion is calculated from maximum radial displacement derived from the Duddeck and Erdmann equations. Based on assumed ground and surcharge loading and using Duddeck and Erdmann equations, the tunnel is currently assumed to have a maximum radial distortion of 2.1mm, or approximately 0.20%. The maximum bending moment, and hoop force derived from the Duddeck and Erdmann equations are 6.6kNm/m and 349kN/m respectively and these are plotted in the interaction diagram to confirm that design assumptions are reasonable as the plotted values should fall inside the diagram, see Figure 4. 4.3.4 Determine change in bending moment in lining due to Thames Tunnel

construction

The tunnel cross-sectional distortion calculated from vertical ‘Greenfield’ ground movements equates to a maximum of 0.023 % ovalisation as shown in Table 4. Experience shows that most tunnels in London clay exhibit “squat” (reduction in tunnel height and increase in tunnel width) following construction. This is likely to be due to a reduction in horizontal stresses around the tunnel caused by excavation of the tunnel (reduced Ko). Construction of the Thames Tunnel will cause the Tower Subway to elongate, i.e. increase in height and decrease in width, in the sagging zone which counterbalances the post-construction squat and reduce the moments in the tunnel lining. The calculated ovalisation of 0.023% is subtracted from the existing diametrical distortion of 0.20%. Using Morgan’s equations (1961), the final maximum bending moment in the tunnel lining will be 5.9kNm/m. For the purpose of the structural assessment the ovalisation due to the Thames Tunnel works is considered to occur in any plane of the tunnel.



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Figure 4: Interaction diagram of existing conditions prior to Thames Tunnel

4.3.5 Check that the axial force/bending moment remains within the capacity envelope

The maximum and minimum factored hoop force calculated by Duddeck and Erdmann and the bending moment described in Section 4.3.4 are plotted together in the interaction diagram. If the moment / hoop thrust plots inside the capacity envelope, this indicates that the lining is within the section capacity. A moment / hoop thrust outside the capacity envelope indicate the lining has insufficient factor of safety.

As shown in Figure 5, the calculated ovalisation will counterbalance the squatted tunnel profile and the existing bending moment will effectively reduce i.e. move to the left in the interaction diagram. This is indicated in the interaction diagram where the red plots represent existing condition and the purple plots represent the Tower Subway after construction of the Thames Tunnel works.

In the hogging zone, the calculated ovalisation will impose additional squat to the already squatted tunnel profile. However, since the imposed ovalisation is no more than 0.010%, the increase in bending moment is minimal and will not impact on the tunnel lining. This can be

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Bending Moment (kNm/m)

Permissible lining capacity

Lining forces existing condition based on Duddeck & Erdmann



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illustrated in Figure 5 where it can be seen that a small increase in bending moment would not move the moment/hoop thrust plot outside the capacity envelope.

Figure 5: Interaction diagram including Thames Tunnel works

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Permissible lining capacity Lining forces existing condition based on Duddeck & Erdmann Lining forces including distortion due to TT construction



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4.3.6 Longitudinal deformation of the tunnel lining and circumferential bolts

In the longitudinal direction, the Tower Subway tunnel lining is assessed based on the procedure presented in Figure 6.

Figure 6: Assessment procedure – Longitudinal direction

4.3.7 Bolt and lining stress check (1st check)

The method is based on calculating the extreme fibre strains at the extrados of the lining and the resulting bolt stress using beam bending theory. This method assumes bending mode only and does not account for shearing due to horizontal axial movement. It should be noted that the imposed radius of curvature is predominately used for an initial screening assessment to establish whether the bolts and lining needs further analysis. If the factor of safety of the bolts and lining is greater than 1, no further assessment is proposed at this stage. However, if the

DETERMINE THE MAXIMUM IMPOSED RADIUS OF CURVATURE FROM “GREENFIELD”

VERTICAL MOVEMENTS

As described in section 3.4.2

USE THIS IMPOSED RADIUS OF CURVATURE TO DETERMINE GAP WHICH OPENS UP

BETWEEN TWO RINGS Assume no circumferential bolts between rings (i.e.

loosened or missing)

CHECK WHETHER THE GAP WILL PRESENT A RISK TO THE TUNNEL BASED ON

GROUND/GROUNDWATER CONDITIONS

USE THIS IMPOSED RADIUS OF CURVATURE TO CALCULATE EXTREME FIBRE STRAIN OF

TUNNEL

Use beam bending theory, ε = r / R

CHECK THE BOLT AND LINING STRESS WITH THEIR ULTIMATE CAPACITY

Assume extension of bolt and lining at extreme

fibre. The limiting stress in the lining is determined by the bolt stresses

1st CHECK

2nd CHECK



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factor of safety is less than 1, further analysis will be undertaken to look at the performance of the bolts and flanges in more detail. The analysis can be summarised in the expression for overall limiting extreme fibre strain from:

𝜀𝑡𝑜𝑡𝑎𝑙 = 𝜀𝑠𝑘𝑖𝑛 + 𝜀𝑏𝑜𝑙𝑡 ×𝐿𝑏𝑜𝑙𝑡𝐿𝑠𝑘𝑖𝑛

Where: εskin = skin strain at limiting allowable bolt stress εbolt = bolt strain at limiting allowable bolt stress Lbolt = length of bolt under tension Lskin = circumferential width of tunnel segment Based on the critical imposed radius of curvature in the sagging mode of 19.6km, the bolt lining stresses required to accommodate this curvature is as follows:

Table 8: Imposed bolt and lining stresses

Distortion mode Sagging Imposed radius of curvature R’ (km) 19.6 Number of circumferential bolts 19 Imposed bolt stress (N/mm²) 85.2 Condition Factor (bolts) 0.9 Bolt stress factor of safety1 3.6 Imposed lining stress (N/mm²) 2.1 Lining stress factor of safety2 65 Condition Factor (lining) 0.9 Notes:

1 The existing stresses in the bolts are unknown and the analysis is based on comparing the imposed stress with the ultimate bolt tensile stress. The ultimate tensile stress (including a condition factor) is 342 N/mm2 x 0.9= 307.8N/mm2

2 The ultimate lining tensile stress = 4 x permissible stress with a lining condition factor of 0.9 = 4 x 0.9 x 38 = 136.8N/mm²

The imposed stresses on the bolt in Table 8 present the limiting case with the calculated bolt stress, in the sagging mode of distortion, having a factor of safety of 3.6 in relation to the ultimate bolt stress of 307.8 N/mm2 (this relates to bolts at the extreme fibre in the invert). Since the factor of safety is greater than 1, the impact on the Tower Subway lining and bolts, due to the Thames Tunnel works, is considered to be minor and no further assessment will be undertake. In addition to the assessment above, a review of case studies, for instance, Burford (1996), Standing & Selman (2001), Vaziri & Steen (2008) which are similar in nature to the proposed Thames Tunnel / Tower Subway interface has been undertaken. No significant damage was noted for the case studies reviewed.



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4.3.8 Gap opening up between rings (2nd check)

The tunnel lining is assessed by examining the maximum gap that can occur between two rings. The imposed radius of curvature is used to calculate the maximum gap due to bending which may open up between rings.

Gap = (bxR)/(R-ø) - b Where b = overall width of section R = imposed radius of curvature Ø = External diameter

The maximum gap from bending at the Tower Subway interface is 0.05mm. However, the maximum gap from bending as explained above together with maximum imposed gap due to horizontal displacement gives a maximum combined gap of 0.17mm. This gap is considered small and since the Tower Subway tunnel is founded in the relatively impermeable London Clay, there is no significant risk associated with opening up of the tunnel joints.

4.3.9 In house structures

The Tower Subway tunnel houses in tunnel structures such as brackets, fibre optic cables and redundant water mains. It is considered that the cables are more flexible than the segmental cast iron lining itself and based on the calculated ground movement, the impact on in tunnel structures is considered likely to be negligible.



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5 Conclusion The assessment described in this report is based on PBA/Arup’s understanding of the proposed Thames Tunnel project. Any recommendations should be considered holistically by the Thames Tunnel project team within the detailed context of the proposed works onsite. The assessment is based on a number of assumptions regarding lining material and properties while the geometry has been taken from archive drawings and from a visual inspection undertaken on the 4th November 2011. The assessment also considers the condition of the lining and a condition factor has been applied to account for corrosion identified during the tunnel inspection. The Tower Subway tunnel is located at a minimum clear distance of 26.5m above the proposed Thames Tunnel. Results from the ground movement assessment in the longitudinal and transverse direction have been used to calculate the resulting stresses imposed on the tunnel lining. The maximum vertical movement is 14.5mm. The current assessment indicates that the impact on the Tower Subway tunnel in both transverse and longitudinal direction is within the lining capacity. The maximum combined gap of 0.17mm which may open up between two segments is considered to cause no risk to the integrity of the tunnel structure. This assessment indicates that the impact on the Tower Subway tunnel due to the Thames Tunnel works is limited. However, since the tunnel lining and bolts show signs of corrosion, it is recommended that a condition survey is carried out after the proposed construction of the Thames Tunnel. This will confirm whether any adverse changes in the condition of the tunnel have occurred as a result of the Thames Tunnel construction. In addition, the need for monitoring during and after excavation will be discussed with the asset owner during the detailed design stage and agreed prior to construction.



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References Tunnel 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.

• Burford (1996). Heave of Bakerloo line tunnels under the Shell building, London. Unpublished BRE report N31/96.

• CIRIA (2001). Building response to tunnelling. Case studies from construction of the Jubilee Line Extension, London. Burland, Standing and Jardine, (eds). Volume 1 – Projects and methods & Volume 2 Case Studies. Includes Standing and Selman (2001) reference taken from this publication.

• Duddeck H. and Erdmann J. (1985), ITA tunnel lining design, On structural design

models for tunnels.

• H J B Harding (1945), Emergency Repair to the Tower Subway, London, after Air-raid damage, Journal of the ICE, Volume 25, Issue 1, pages 73 –79

• Mair, R., Taylor, R. & Bracegirdle, A (1993), Sub-surface settlement profiles above tunnels in clays, Geotechnique, Vol. 43 No. 2, pp 315-320.

• Mayne, P. and Kulhawy, F. (1982), K0 – OCR Relationship in soil.

• Morgan H. (1961), A contribution to the analysis of stress in a circular tunnel, Geotechnique, Vol.11, No. 1pp 37-46.

• Standing and Selma (2001), Building Response to Tunnelling, Case Studies from construction of the Jubilee Line Extension, London, Volume 2, Chapter 29,

• 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.

• M. Vaziri, T. Hartlib (2008). BBC W1 Development Case Study – Tunnel Movement Class A Predictions. The 12th International Conference of International Association for Computer Methods and Advances in Geomechanics (IACMAG) Goa, India.

• Wongsaroj J et al (2006), Effect of TBM driving parameters on ground surface movements: Channel Tunnel Rail Link Contract 220, Proc. Geotechnical Aspects of Underground Construction in Soft Ground pp 335-341

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Appendix A – Calculations

Printed on:09:44 19/03/2012File name:TowerSubway_TunnelAssessment_post TT_rev1.xlsx

Job No. Sheet No. Rev.

215748-00 1.0 1

Member/Location

Job Title Thames Tunnel - Tower Subway Assessment Drg. Ref.

Post Thames Tunnel construction Made by YKL Date 19-Mar-12 Chd.

1.0 Input DataMaterials Young's Modulus of cast iron, Ecast iron = 112 500 MPa

Poissons ratio of cast iron, νcast iron = 0.26Permissible compressive strength of cast iron Rp in c. = 150 N/mm²

Permissible tensile strength of cast iron, Rp in t= 38 N/mm²Material safety factor for cast iron = 1.00

Elastic Modulus of ground, Ec= 40 MPaPoissons ratio of ground, ν= 0.20

Tunnel geometry internal diameter, D = 2 134 mm ext. dia, ED = 2 295 mmoverall depth of section, h = 81 mm

internal depths for gaskets: internal, iint = 0 mm, external, iext = 0 mmdepth of skin, hf = 31 mm

length of centre rib, hr = 0 mmoverall width of section, b = 448 mm

total width of ribs, bw = 48 mm from: rib 1, t1 = 24 mmrib 2, t2 = 0 mm

Density of cast iron = 7 200 kg/m3 rib 3, t3 = 24 mmnumber of segments, n = 3

angle subtended by segment, β = 120 ºCondition factor Fc = 0.9 from LU G-055

Loading GL= 91.03 mTD Factored Loads Unfactored Loads

GWL = 69.27 mTD 316.728 263.94 (vert. tot stress)Tunnel axis level = 84.35 mTD 0 0 (pwp)

Unit weight of soil = 20 kN/m3 316.728 263.94 (vert eff. Stress)K = 0.7 221.71 184.76 (hor. eff. stress)

Surface surcharge = 130.34 kPa 221.71 184.76 (hor. tot. stress)Partial factor on overburden = 1.2

Partial factor on surcharge = 1.2Vertical Pressure at the Axis Pfv= 316.73 kPa Puv= 263.94 kPa

Horizontal Pressure at the Axis Pfh= 221.71 kPa Puh= 184.76 kPa

Duddeck and Erdmann analysisThe continuum model derived by Duddeck and Erdmann is use to derive the forces and moments in the lining. This model gives different equations for (a) full bond between the lining and the ground, and (2) tangential slip. The type of analysis used in this spreadsheet need to be input in the box below.

If full bond is to be used type F, if not type T for tangential slip FFull bond has been specified

Ovalisation due to Thames Tunnel construction - from XDISP or other calculationsmaximum "squat" = 0.00023 of internal radius

∴ maximum radial displacement, u2ϕ = -0.25 mm

Bolt geometryDiameter of bolt, Dbolt = 19 mm Ult. Tensile, Ubolt = 342 N/mm²

Length of bolt, Lbolt = 115 mm Ult. Shear, Sbolt=0.4Ubolt = 137 N/mm²Cross sectional area, Abolt = 283.53 mm2 Young's Modulus, Ebolt = 190 GPa

Number of circumferential bolts = 19 Material factor Mbolt= 1.2Number of radial bolts = 6 Opening assessment required Y or N? N

No. of bolts around the ring act in shear, Ns=Size of bolt hole, Dbolt hole = 25.4 mm Number of rings in opening, No = Input data

Cast-iron bolted

Lining Assessment Spreadsheet

Printed on:09:44 19/03/2012File name:TowerSubway_TunnelAssessment_post TT_rev1.xlsx


215748-00 3.1 1

Member/Location 0

Job Title Thames Tunnel - Tower Subway Assessment Drg. Ref. 0Post Thames Tunnel construction Made by YKL Date 19-Mar-12 Chd.

3.1 Duddeck and Erdmann analysis (Ie) - consider the effect of panels for lining stiffnessInput parameters:Ground: Elastic Modulus Ec= 40 MPa

Poisson's Ratio ν = 0.20Lining: Radius of Centroid ro= 1.12624 m

Elastic Modulus E= 120656 MPa E=Ecast iron/(1-νcast iron2) - Muir Wood

Effective Moment of Inertia Ie= 1.09E-05 m4/mSectional Area A= 0.03586 m2/m

Loading: Factored Loads Unfactored LoadsVertical Pressure at the Axis Pfv= 316.73 kPa Puv= 263.94 kPa

Horizontal Pressure at the Axis Pfh= 221.71 kPa Puh= 184.76 kPaTheory:The loading on the lining is calculated using the Duddeck and Erdmann analysis. These equations alloweither full bond between the lining and the ground, or tangential slip. This is selected below based on anappreciation of the behaviour of the ground Full bond specified F

Duddeck and Erdmann FormulaeFull Bond Tangential Slip

(Derived from Nav)

Results Factored Unfactored Bending Moment+/- M= 6.58 kNm/m M= 5.48 kNm/m

Average Hoop Thrust Nav= 302.16 kN/m Nav= 251.94 kN/mVariable Hoop Thrust+/- Nvar= 47.07 kN/m Nvar= 39.23 kN/m

Constant Radial Displacement Uo= 0.08 mm Uo= 0.07 mmMax, Radial Displacement Umax= 2.12 mm Umax= 1.77 mm

Relative Flexibility Factor Q2= 3.03 Q2= 3.03Design Shear(Lining/Ground) T= 73.22 kPa T= 61.01 kPa

Moments and Hoop Stresses Induced in the Lining factored maximum hoop load, Nfmax = 349 kN/m (or 0.349 MN/m) factored minimum hoop load, Nfmin = 255 kN/m (or 0.255 MN/m)

unfactored maximum hoop load, Numax = 291 kN/m (or 0.291 MN/m)unfactored minimum hoop load, Numin = 213 kN/m (or 0.213 MN/m)

factored maximum moment, Mfmax = 6.6 kNm/m 6.58 -6.58unfactored maximum moment, Mumax= 5.5 kNm/m 5.48 -5.48

Duddeck and Erdmann (lining stiffness considering segments)

(σv-σh)R 2+ 4νEcR3/EJ (3-4ν)(12(1+ν)+EcR3/EJ)

0.5(σv+σh)R2 (1-υ)(1-K0)EcR3 + EA

(1-2υ)(1+υ)

(σv-σh)R4/EJ

12+ 3-2ν EcR3 (1+ν)(3-4ν) EJ

.

(σv-σh)R2

4+ 3-2ν EcR3 3(1+ν)(3-4ν) EJ

.

(σv-σh)R2

10-12ν + 2 EcR3 3-4ν 3(1+ν)(3-4ν) EJ

.

(σv+σh)R

2+ 2(1-ν)(1-K0) EcR (1-2ν)(1+ν) EA

.

(σv-σh)R

10-12ν + 2 EcR3 3-4ν 3(1+ν)(3-4ν) EJ

.

(σv-σh)R4/EJ

6(5-6ν) + 2 EcR3 3-4ν (1+ν)(3-4ν) EJ

.

Average hoop thrust

Nav

Variable hoop thrust

Nvar

Constant radial displacement

u0

Maximum radial displacement

u2ψ

Maximum bending

moment,M

Cast-iron bolted


Printed on: 09:44 19/03/2012File: TowerSubway_TunnelAssessment_post TT_rev1.xlsx


215748-00 5.1 1

Member/Location 0


5.1 Comparison of actual loads with lining capacity: consider the effect of panels

The capacity graph from section 2.0 is reproduced here, with the loads calculated plotted on.All loads are factored.

Capacity vs Actual (lining stiffness considering segments)

0.00

1.00

2.00

3.00

4.00

5.00

6.00

-30.00 -20.00 -10.00 0.00 10.00 20.00 30.00

Axia

l For

ce (M

N/m

)




Lining forces including distortion due to TT construction

I=Ie

Cast-iron bolted


using Duddeck & Erdmann equation to calculate existing BM

Printed on: 09:44 19/03/2012 File: TowerSubway_TunnelAssessment_post TT_rev1.xlsx


215748-00 6.0 1

Member/Location 0


6.0 Longitudinal curvatureCHECK 1

σ = M yextreme / I yextreme = dist. between neutral axis and extreme fibre 1520.4 mmε = M yextreme / E I I = Second moment of area of tunnel section

Three modes of tensile strain are considered: a) The strain assuming the lining only deforms and reaches its permissible stress.

The radius of curvature, R', can be calculated as:R' = EI /M

R' limiting = E yextreme / σpermissible Lining σpermissible = 34 N/mm2

a) assume lining failure only, y extreme = external radius of the tunnelε lining, limiting = σpermissible/E = 2.83E-04 where E= 120656 MPa (for lining)

R' limiting = r/ ε lining, limiting= 4048 m (for information)

b) assume strain of lining at bolt allowable stress, yextreme = external radius of the tunnelassume working bolt stress σbolt= 85.5 N/mm2 (= Ult ten./4 (BCIRA))

Cross-section area of bolt = 283.529 mm2 Maximum force per bolt = 24.242 kNSkin area = 216981 mm2

Number of circumferential bolts = 19 Skin area per bolt = 11420 mm2Stress on the lining from a single bolt (at the bolts allowable stress) = 2.1227 N/mm2

From aboveε lining, limiting = σlimited by bolt stress/E = 1.76E-05 where E= 120656 MPa (for lining)

R' limiting = r/ ε lining, limiting= 65224 m (for information)

c) consider the strain along the extreme fibre bolt and lining and calculate required bolt stress using εtotal = εlining + εbolt * Lbolt / Llining and yextreme = 1520.4 mm

where εlining = lining strain at limiting allowable bolt stressεbolt = bolt strain at limiting allowable bolt stressLbolt = length of bolt under tension assume 0.06 m, between the nut and head of boltLlining = circumferential width of tunnel segment = 0.448 m

imposed radius of curvature = 19600 m Manual inputεtotal = 8E-05Ebolt = 190 GPa

Elining = 121 GPa

Required bolt stress = 85.182 N/mm2 okImposed lining stress = 2.11 N/mm2 ok

CHECK 2calculate the size of gap if the circumferential bolts are not considered (i.e. missing or loosen bolts)

gap = 2b * Rimposed / (Rimposed - ED) - 2b= 0.1049 mm

Longitudinal - Radius of curvature

b) The strain assuming the lining deforms based on the limiting stress caused by the bolt reaching its allowable stressc) The required bolt stress at the imposed radius of curvature assuming that both the lining and bolt deform

Assume the tunnel is a continuous flexible tube, the extreme fibre stress and strain of a tunnel section can be calculated as follows:

Cast-iron bolted


Printed on:09:43 19/03/2012File name:TowerSubway_TunnelAssessment_pre TT_rev1.xlsx


215748-00 1.0 1

Member/Location

Job Title Thames Tunnel - Tower Subway Assessment Drg. Ref.

Post Thames Tunnel construction Made by YKL Date 19-Mar-12 Chd.

1.0 Input DataMaterials Young's Modulus of cast iron, Ecast iron = 112 500 MPa

Poissons ratio of cast iron, νcast iron = 0.26Permissible compressive strength of cast iron Rp in c. = 150 N/mm²

Permissible tensile strength of cast iron, Rp in t= 38 N/mm²Material safety factor for cast iron = 1.00

Elastic Modulus of ground, Ec= 40 MPaPoissons ratio of ground, ν= 0.20

Tunnel geometry internal diameter, D = 2 134 mm ext. dia, ED = 2 295 mmoverall depth of section, h = 81 mm

internal depths for gaskets: internal, iint = 0 mm, external, iext = 0 mmdepth of skin, hf = 31 mm

length of centre rib, hr = 0 mmoverall width of section, b = 448 mm

total width of ribs, bw = 48 mm from: rib 1, t1 = 24 mmrib 2, t2 = 0 mm

Density of cast iron = 7 200 kg/m3 rib 3, t3 = 24 mmnumber of segments, n = 3

angle subtended by segment, β = 120 ºCondition factor Fc = 0.9 from LU G-055

Loading GL= 91.03 mTD Factored Loads Unfactored Loads

GWL = 69.27 mTD 316.728 263.94 (vert. tot stress)Tunnel axis level = 84.35 mTD 0 0 (pwp)

Unit weight of soil = 20 kN/m3 316.728 263.94 (vert eff. Stress)K = 0.7 221.71 184.76 (hor. eff. stress)

Surface surcharge = 130.34 kPa 221.71 184.76 (hor. tot. stress)Partial factor on overburden = 1.2

Partial factor on surcharge = 1.2Vertical Pressure at the Axis Pfv= 316.73 kPa Puv= 263.94 kPa

Horizontal Pressure at the Axis Pfh= 221.71 kPa Puh= 184.76 kPa

Duddeck and Erdmann analysisThe continuum model derived by Duddeck and Erdmann is use to derive the forces and moments in the lining. This model gives different equations for (a) full bond between the lining and the ground, and (2) tangential slip. The type of analysis used in this spreadsheet need to be input in the box below.

If full bond is to be used type F, if not type T for tangential slip FFull bond has been specified

Ovalisation due to Thames Tunnel construction - from XDISP or other calculationsmaximum "squat" = 0.00023 of internal radius

∴ maximum radial displacement, u2ϕ = -0.25 mm

Bolt geometryDiameter of bolt, Dbolt = 19 mm Ult. Tensile, Ubolt = 342 N/mm²

Length of bolt, Lbolt = 115 mm Ult. Shear, Sbolt=0.4Ubolt = 137 N/mm²Cross sectional area, Abolt = 283.53 mm2 Young's Modulus, Ebolt = 190 GPa

Number of circumferential bolts = 19 Material factor Mbolt= 1.2Number of radial bolts = 6 Opening assessment required Y or N? N

No. of bolts around the ring act in shear, Ns=Size of bolt hole, Dbolt hole = 25.4 mm Number of rings in opening, No = Input data

Cast-iron bolted


Printed on:09:43 19/03/2012File name:TowerSubway_TunnelAssessment_pre TT_rev1.xlsx


215748-00 3.1 1

Member/Location 0


3.1 Duddeck and Erdmann analysis (Ie) - consider the effect of panels for lining stiffnessInput parameters:Ground: Elastic Modulus Ec= 40 MPa

Poisson's Ratio ν = 0.20Lining: Radius of Centroid ro= 1.12624 m

Elastic Modulus E= 120656 MPa E=Ecast iron/(1-νcast iron2) - Muir Wood

Effective Moment of Inertia Ie= 1.09E-05 m4/mSectional Area A= 0.03586 m2/m

Loading: Factored Loads Unfactored LoadsVertical Pressure at the Axis Pfv= 316.73 kPa Puv= 263.94 kPa

Horizontal Pressure at the Axis Pfh= 221.71 kPa Puh= 184.76 kPaTheory:The loading on the lining is calculated using the Duddeck and Erdmann analysis. These equations alloweither full bond between the lining and the ground, or tangential slip. This is selected below based on anappreciation of the behaviour of the ground Full bond specified F

Duddeck and Erdmann FormulaeFull Bond Tangential Slip

(Derived from Nav)

Results Factored Unfactored Bending Moment+/- M= 6.58 kNm/m M= 5.48 kNm/m

Average Hoop Thrust Nav= 302.16 kN/m Nav= 251.94 kN/mVariable Hoop Thrust+/- Nvar= 47.07 kN/m Nvar= 39.23 kN/m

Constant Radial Displacement Uo= 0.08 mm Uo= 0.07 mmMax, Radial Displacement Umax= 2.12 mm Umax= 1.77 mm

Relative Flexibility Factor Q2= 3.03 Q2= 3.03Design Shear(Lining/Ground) T= 73.22 kPa T= 61.01 kPa

Moments and Hoop Stresses Induced in the Lining factored maximum hoop load, Nfmax = 349 kN/m (or 0.349 MN/m) factored minimum hoop load, Nfmin = 255 kN/m (or 0.255 MN/m)

unfactored maximum hoop load, Numax = 291 kN/m (or 0.291 MN/m)unfactored minimum hoop load, Numin = 213 kN/m (or 0.213 MN/m)

factored maximum moment, Mfmax = 6.6 kNm/m 6.58 -6.58unfactored maximum moment, Mumax= 5.5 kNm/m 5.48 -5.48

Duddeck and Erdmann (lining stiffness considering segments)

(σv-σh)R 2+ 4νEcR3/EJ (3-4ν)(12(1+ν)+EcR3/EJ)

0.5(σv+σh)R2 (1-υ)(1-K0)EcR3 + EA

(1-2υ)(1+υ)

(σv-σh)R4/EJ

12+ 3-2ν EcR3 (1+ν)(3-4ν) EJ

.

(σv-σh)R2

4+ 3-2ν EcR3 3(1+ν)(3-4ν) EJ

.

(σv-σh)R2

10-12ν + 2 EcR3 3-4ν 3(1+ν)(3-4ν) EJ

.

(σv+σh)R

2+ 2(1-ν)(1-K0) EcR (1-2ν)(1+ν) EA

.

(σv-σh)R

10-12ν + 2 EcR3 3-4ν 3(1+ν)(3-4ν) EJ

.

(σv-σh)R4/EJ

6(5-6ν) + 2 EcR3 3-4ν (1+ν)(3-4ν) EJ

.

Average hoop thrust

Nav

Variable hoop thrust

Nvar

Constant radial displacement

u0

Maximum radial displacement

u2ψ

Maximum bending

moment,M

Cast-iron bolted


Printed on: 09:43 19/03/2012File: TowerSubway_TunnelAssessment_pre TT_rev1.xlsx


215748-00 5.1 1

Member/Location 0


5.1 Comparison of actual loads with lining capacity: consider the effect of panels

The capacity graph from section 2.0 is reproduced here, with the loads calculated plotted on.All loads are factored.

Capacity vs Actual (lining stiffness considering segments)

0.00

1.00

2.00

3.00

4.00

5.00

6.00

-30.00 -20.00 -10.00 0.00 10.00 20.00 30.00

Axia

l For

ce (M

N/m

)




I=Ie

Cast-iron bolted


using Duddeck & Erdmann equation to calculate existing BM



Printed 19/03/2012

Appendix B – Drawings

60 60

215748-00APR. '11 SKETCH 1215748-00

CABLE & WIRELESS TOWER SUBWAY 1870 “GREENFIELD” GROUND SETTLEMENT 1.0% VL

25mDistance of inspection

beyond 1mm contour lineDistance of inspection

beyond 1mm contour line

25m

14.5

mm

Inspection Zone (~130m)

Scale 1:200

NOTE: 1. SETTLEMENT TROUGH VERTICALLY EXAGGERATED FOR CLARITY .2. DO NOT SCALE FROM DRAWING



Printed 19/03/2012

Appendix C – Risk Register

Hazard Risk Register

J:\200000\215748-00\50_DESIGN_ANALYSIS\TOWER SUBWAY\DETAILED ASSESSMENT\TOWER SUBWAY REV AE\APPENDIX C\HAZARD RISK REGISTER_TU014 TOWER SUBWAY_REV AC.DOCX

Page 1 of 5 ©Arup | F18.2a | Rel 14.2 14 February 2011

Register reference

Project Thames Tunnel Detailed Assessment Package 2a Job number 215748-00

Package/Topic Tower Subway Crossing Design stage

Remember: Avoid – Reduce – Control and communicate relevant information to others (CDM Regulation 11)

Date Area/Location of Risk Exposure

Description of Hazard and Risk Exposure

Mitigation of Risk (Potential or Achieved) A R C Further Action by

Status

(+ initials) Active/closed

Thames Tunnel (TT) excavation below Tower Subway (TS) tunnel

Unidentified geological anomalies may cause water ingress during tunnel excavation and the risk of ground movement at the above TS tunnel increases.

• Desk study to identify geological anomalies

• Boreholes to confirm strata at TT face and TT/TS interface

√ TT to issue desk study TT to drill borehole at TT/TS interface

Tower Subway tunnel lining

The London Clay strata is more permeable than anticipated and water ingress could occur through the gap which may open up between segments.

• Boreholes at tunnel interface to identify sand lenses in the London Clay strata

√ TT to drill borehole at TT/TS interface


The assumed lining dimensions are incorrect and the structural capacity is overestimated. The induced impact on the TS tunnel may exceed the lining capacity.

• A visual inspection of the tunnel has been undertaken to confirm dimensions for the flange

√ No further actions




Register reference







Status


thickness, rib and skin thickness for the detailed assessment.

• Base detailed assessment on As-built drawings


The assumed cast iron strength is incorrect and the structural capacity is overestimated. The induced impact on the TS tunnel may exceed the lining capacity.

• Use conservative cast iron strength parameters

• Use London Underground recommended parameters for the assessment

√ TT (Cable & Wireless) to confirm cast iron grade and strength.


The assumed Young’s modulus for cast iron is incorrect and the structural capacity is overestimated. The induced impact on the TS tunnel may exceed the lining capacity.

• Use London Underground recommended parameters for a conservative Young’s Modulus.

√ TT (Cable & Wireless) to confirm cast iron grade.




Register reference







Status


Tower Subway tunnel bolts

The existing tensile forces in the circumferential bolts are not known. If there is significant pre-existing force in the bolt, then small increments of tensile stress caused by ground movement may potentially caused the bolt or flange to break.

• Case studies referenced in the report highlight several instances where cast iron tunnels have been subjected to larger distortions and no damage has been noted.

• There is no reason to believe that significant torque was applied to bolts when fastened.

√

Tower Subway tunnel bolts

For assessing the longitudinal distortion, only initial screening assessments have been carried out. These use of an ‘index’ parameter (radius of curvature) to

• The effects on the circumferential bolts indicate that the stresses do not result in a FOS of less than 1.

√




Register reference







Status


appraise the effect of longitudinal distortion and effects on the circumferential bolts and skin has been used. No check on stresses on the flanges or account for longitudinal axial stresses has been accounted for in the assessment.

Comparisons with other case studies indicate that greater levels of distortion have resulted in no appreciable impact on cast iron tunnels. It is also likely that the vertical movements result in a combination of both bending and shearing. The initial check using an initial ‘index’ parameter such as the radius of curvature is considered to be a reasonable approach for an initial assessment, thereafter, consideration of other modes of




Register reference







Status


deformation should be considered in greater detail.



Printed 19/03/2012

Appendix D – Inspection Report

307-RI-TPI-TU014-000001| AB| 25 November 2011

Cable & Wireless Tower Subway Tunnel Crossing

Inspection report

Inspection Report for Cable & Wireless Tower Subway Crossing

i Printed 25/11/2011

Table of contents

Page number

1 Executive summary ............................................................................................. 3

2 Introduction........................................................................................................ 4

3 Tunnel construction ............................................................................................ 5

4 Tunnel inspection ................................................................................................ 6

4.1 Scope of inspection .................................................................................... 6

4.2 Access and limitations ................................................................................ 7

5 Observations ....................................................................................................... 8

5.1 General condition ....................................................................................... 8

5.2 Tunnel geometry ........................................................................................ 8

Appendices .................................................................................................................. 9

Appendix D1 – Figures ....................................................................................... 10

Appendix D2 - Ring observations ......................................................................... 11

Appendix D3 – Photographs ................................................................................ 12


ii Printed 25/11/2011

List of tables Page number

Table 1 - Inspection team ............................................................................................... 6

Table 2 - Tunnel geometry ............................................................................................. 8

Cable & Wireless - Tower Subway Tunnel Crossing


3 Printed 25/11/2011

1 Executive summary Thames Water is currently progressing with its planned Tideway improvements. The improvement works consists of the construction of two new tunnels, the Thames Tunnel and the Lee Tunnel, together with a programme of sewer upgrades. Construction of the proposed Thames Tunnel (TT), an 8.1m – 8.8m excavated diameter tunnel, stretching approximately 23km for much of its route under the River Thames from West London to Abbey Mills is due to commence in 2014.

The proposed interface between the Thames Tunnel and the Tower Subway tunnel is located in the middle of the River Thames. The Thames Tunnel will be constructed below the Tower Subway with a clear distance of 26.5m between the two tunnels.

To date, an interim detailed assessment report has been issued to the Thames Tunnel team to assess the likely impact on the Tower Subway due to the construction of the Thames Tunnel. The interim report is based on a number of assumptions regarding the tunnel lining geometry and tunnel condition. In order to confirm these assumptions and to record the condition of the tunnel, a visual inspection of the Tower Subway was undertaken on Friday 4th November 2011.

The inspection indicates that the cast iron segments show a fairly high degree of pitting corrosion in some areas which has affected the pans, flanges and particularly the bolt heads. It is not considered that the corrosion is severe enough to impact on the cast iron lining properties. However, since the bolts are highly corroded the capacity of the bolts is unlikely to be as competent as for non corroded bolts.



4 Printed 25/11/2011

2 Introduction The Tower Subway tunnel is located west of Tower Bridge. The tunnel runs between the south shaft, located off Tooley Street, to the north shaft near Tower Hill by the Tower of London. The tunnel is located approximately 6m below river bed level.

The Tower Subway tunnel is currently owned by Cable and Wireless and is used for carrying communications cables and redundant water mains beneath the River Thames. Cable & Wireless has appointed Mitie Engineering Limited as the main contractor for the maintenance of the Tower Subway tunnel. Mitie employs Jascom Electrical Contractors Limited to carry out access and maintenance of the tunnel

The proposed interface between the Thames Tunnel and the Tower Subway tunnel is located in the middle of the River Thames. The 8.8m excavated diameter Thames Tunnel will be constructed below the Tower Subway with a clear distance of 26.5m between the two tunnels.

As part of the assessment of the Tower Subway, a visual inspection will be undertaken to confirm assumptions made in the detailed analysis and to record the general condition of the tunnel lining and bolts. The tunnel inspection is limited to a zone, extending approximately 65m on either side of the tunnel interface. This zone represents the length of the Tower Subway tunnel which is subject to ground movement greater than 1mm. An additional 25m has been added on either side to ensure that a sufficient length of the tunnel is inspected, see Sketch 1 in Appendix D1.



5 Printed 25/11/2011

3 Tunnel construction The Tower Subway was constructed in 1869 between Tower Hill and Vine Street, by James Henry Greathead. It has the distinction of being the first ‘tube tunnel’ constructed in the world; a technique whereby a circular excavating shield was advanced through the ground and a tunnel lining constructed using segmental cast iron sections. The lining in the Tower Subway is formed from bolted cast iron rings and comprises 3 larger segments plus a key at the crown. At either end of the Tower Subway, the tunnel increased in diameter to form a waiting room for passengers, approximately 7.5m long.

The Tower Subway was used for passenger transport across the Thames for only a short period of time before it was made redundant by the opening of Tower Bridge in 1894. The tunnel was subsequently purchased by the London Hydraulic Power Company to convey 2 hydraulic cast iron mains (7” and 10” diameter) which are now redundant but remain in the Tower Subway. During this period of ownership, an agreement was made with the Metropolitan Water Board to install a 20” diameter cast iron main (in 1898), and later a 24”steel main (in 1924) in the tunnel. More recently, the tunnel leasehold has been purchased by Cable and Wireless Communications Services Ltd and has been used to carry fibre optic cables.

In 1988, an extension to the tunnel as well as a new shaft was constructed near Tooley Street. Both the new tunnel and shaft were constructed using pre-cast concrete segmental linings. The original access shaft to the Tower Subway was backfilled following the construction of the extension.

It should be noted that the visual inspection did not include the enlarged tunnel sections or the shafts.



6 Printed 25/11/2011

4 Tunnel inspection An inspection of the Tower Subway tunnel was carried out on Friday 4th November 2011 between 8am and 4pm. The inspection team consisted of Arup Tunnel Engineers with safety personnel from Jascom Electrical Contractors (on behalf of Mitie Engineering Limited).

Table 1 - Inspection team

Name Company Role

Linn Nordstrom

Arup Tunnel Inspector

Yung Loo Arup Tunnel Inspector

7x Jascom personnel

Jascom Electrical Contractors Limited (appointed by Mitie)

Tunnel escort, top men and rescue team

A method statement had been prepared for the tunnel entry protocol and safety, and this was fully complied with by all parties.

The weather on the morning of inspection was rainy and it had rained during the night. The weather improved during the course of the inspection and the rain stopped mid-morning.

The inspection was undertaken from the north to the south, however, the inspection team only used the south shaft for access and egress.

4.1 Scope of inspection

The scope of the inspection was to undertake a visual observation of the tunnel lining to confirm the lining geometry and to determine the presence of any signs of distress or damage that may compromise the structural capacity of the tunnel. Such features include but are not limited to; cracking / spalling of tunnel segments; corrosion of tunnel segments; water ingress; and birdsmouthing of segments.

The visual inspection consisted of a walkthrough with notes and photographs taken where necessary to flag up any potential areas of concern.

It should be noted that the inspection was not intended to be a full structural survey or an intrusive investigation. The following information was recorded as a minimum:

Tunnel details including;

• Location

• Lining Type Tunnel Lining

• Segment and key position

• Segment dimensions



7 Printed 25/11/2011

• Identify defects, major (cracked segments, spalled concrete joints) and minor (seepage and corrosion)

• Lipping / stepping

• Evidence of previous repairs including bolt loosening or removal.

4.2 Access and limitations

It should be noted that the visual inspection did not include the enlarged tunnel sections or the shafts. The area of inspection was limited to;

• 280 rings of the cast iron tunnel centred on the Thames Tunnel crossing beneath the River Thames

As discussed in Section 3, the tunnel contains four water mains which obscured significant portions of the tunnel lining. The findings of this inspection are therefore based on those portions of the tunnel that were visible at the time of the visit.



8 Printed 25/11/2011

5 Observations The findings of the inspections are summarised below. Recorded observations for each ring are included in Appendix D2 whilst Appendix D3 contains photographs of some of the defects observed.

5.1 General condition

The survey started near the north shaft and for ease of reference the location of the first ring coincides with the location of the electrical light with reference number L43.

The tunnel was naturally ventilated during the inspection and the pumps were in operation to reduce the water level. Water was encountered in the invert between Ring 91 and Ring 188, reaching a maximum depth of about 50mm at Ring 110. The rest of the tunnel invert was dry.

The cast iron segments show a fairly high degree of pitting corrosion which has affected the pans, flanges and particularly the bolt heads, most of which have substantial degradation due to corrosion (e.g. Photo 40 & 43). Due to the location of the redundant water mains, it was not possible to inspect the tunnel axis or knee in great detail (e.g. Photo 17 & 37); however it was clear that the corrosion at the tunnel crown is much greater than at tunnel axis or knee.

No active seepage was recorded in the tunnel. However, stalactites and calcite build up were visible, indicating evidence of previous water ingress. A description of observations is presented in Appendix D2. Photographs of observations are presented in Appendix D3.

5.2 Tunnel geometry The following measurements and observations in regards to the tunnel geometry were made during the inspection.

Table 2 - Tunnel geometry

Parameter Value No segments 3 Segment type Cast Iron Segment width 448mm Segment length 910mm Bolts per circumferential joint 3 Total:13 (observed), 19 (expected) Bolts per radial joints 2 Total: 5 (observed), 6 (expected) Bolt diameter Nut: 32mm | Thread: 19mm Bolt Length 115mm Depth of flange 50mm Thickness of skin 30mm Thickness of flange 24mm Notes:

Appendices


9 Printed 23/11/2011

Appendices

Appendices


10 Printed 23/11/2011

Appendix D1 – Figures

60 60

215748-00APR. '11 SKETCH 1215748-00

CABLE & WIRELESS TOWER SUBWAY 1870 “GREENFIELD” GROUND SETTLEMENT 1.0% VL

25mDistance of inspection

beyond 1mm contour lineDistance of inspection

beyond 1mm contour line

25m

14.5

mm

Inspection Zone (~130m)

Scale 1:200

NOTE: 1. SETTLEMENT TROUGH VERTICALLY EXAGGERATED FOR CLARITY .2. DO NOT SCALE FROM DRAWING

Appendices


11 Printed 23/11/2011

Appendix D2 - Ring observations

ArupTower Subway Crossing - Cable and Wireless Tunnel AssessmentCondition survey results

Job No. 215748 Sheet 1/5

TU014 - Tower Subway CrossingLegend: 1 = cracking 2 = corrosion 3 = rust or other staining

4 = calcite buildup 5 = water ingress / evidence of 6 = missing caulking7 = displacement of segments 8 = open joints 9 = loose or missing bolts10 = seepage at grout holes 11 = seepage at joints 12 = seepage at bolt holes

Date: 4th November 2011Surveyor: LN/YL

Ring Number LK LA LS K RS RA RK Notes Photo

It should be noted that the inspection was carried out from the north side to the south side. Ring 1 is located approximately 160m from the north shaft.

1 Location of Light no. L4323456789

10 1-51112131415 2 61617181920 7 Damage at bolt hole2122 4 Location of Light no. L42 723242526272829303132333435 83637383940 Location of Light no. L41 9,104142434445 5 High Stalactite Buildup 114647484950 2 Bolt highly corroded51525354555657585960616263 6 12,1364656667 4,5 1468697071727374

Corrosion, rusting, condensation and evidence of water ingress occurred throughout. The following additional observations were noted where there was an excess or lack of these conditions. Restricted viewing at LK,LA,RK,RA due to presence of redundant water main pipes.

Reduced Corrosion






Ring Number LK LA LS K RS RA RK Notes Photo7576777879808182 1583 1584 1585868788899091 2 Pooling of water at invert until ring 18892 293949596 2,5 Highly corroded bolts and buildup of stalactites979899

100 16101 4 4102 4 4103 4 4104105106 2 2 2 Highly corroded bolts107108109110 High condensation @key | Deep pooling of water at invert (2")111 High condensation @key112113114115116117118119120 17121 18122 19123 19124 20125 21126127128129130131132133134135136 22137 2 22138 2139 2 Location of Light no. L39140141142 3 buildup @bolts143144145146147 3 Highly corroded bolts 23148149150 Reduced Corrosion 24,25151152153154

Reduced Corrosion

Reduced Corrosion

Reduced Corrosion






Ring Number LK LA LS K RS RA RK Notes Photo155156157158159160161162163164165 7 7 mm stepping between flange 26,27166167168169170171172173174175176177178 Location of Light no. L34179180 28181182 2183184185186187188 Dry Invert: Pooling of water at invert ends189190191192 5 High stalactite buildup 29193194195196197 Reduced Corrosion 30-33198199 High Condensation 2 Location of Light no. L33 34200 Corrosion on segments reduced until ring 320 | bolts corroded throughout201202203204205206207208209210211212213214215216 2217218219220 2,high condensation221222223224225226227228229 2230231232233234 35






Ring Number LK LA LS K RS RA RK Notes Photo235 36236237238239240241242243244245246 2247248249 37250251252253254255256 2257258259260 Increased Condensation261262263264 5265266267268269270 38271 38272 2 5 Stalactite buildup @K 39273274275276277278279280 40-44281 41-44282283284285286287 Location of Light no. L40288289290291292 12293294295296297298 Location of Light no. L28299300 2301302303304305306307308309310311312313314

Reduced Corrosion

Reduced Corrosion






Ring Number LK LA LS K RS RA RK Notes Photo315316317318319320 Location of Light no. L27

Appendices


12 Printed 23/11/2011

Appendix D3 – Photographs

Appendices


13 Printed 23/11/2011

Photo 1 – Corrosion at left shoulder of Ring 10

Photo 2 – Corrosion at key of Ring 10

Appendices


14 Printed 23/11/2011

Photo 3 – Corrosion at key of Ring 10


Appendices


15 Printed 23/11/2011


Photo 6 – Corrosion at key of ring 15 and 16.

Appendices


16 Printed 23/11/2011

Photo 7 – Calcite buildup at the right hand shoulder of ring 22.

Photo 8 – Corrosion at crown of ring 35

Appendices


17 Printed 23/11/2011

Photo 9 – Southwards view down tunnel taken from ring 40

Photo 10 – Southwards view down tunnel taken from ring 40

Appendices


18 Printed 23/11/2011

Photo 11 – Stalactite build up at ring right shoulder of ring 45

Photo 12 – Missing caulking at right axis of ring 63

Appendices


19 Printed 23/11/2011

Photo 13 – Missing caulking at right axis of ring 63

Photo 14 – Calcite build up and seepage around bolt at ring 67

Appendices


20 Printed 23/11/2011

Photo 15 – Reduced corrosion (compared to adjacent segments) at right hand shoulder

segments of rings 82-84

Photo 16 – Corrosion at bolt of left hand shoulder at ring 100.

Appendices


21 Printed 23/11/2011

Photo 17 – View towards south from ring 120 looking onto sump.

Photo 18 –Build up of calcite and rusting on right hand axis of ring 121.

Appendices


22 Printed 23/11/2011

Photo 19 – Corrosion at crown of ring 122-123.

Photo 20 – Reduced corrosion (compared to adjacent segments) at right hand shoulder of ring

124

Appendices


23 Printed 23/11/2011

Photo 21- Reduced corrosion (compared to adjacent segments) at left hand shoulder of ring

124.

Photo 22 – Change from decrease in corrosion (compared to adjacent segments) at ring 136

(right) to increase in corrosion (compared to adjacent segments) at ring 137 (left)

Appendices


24 Printed 23/11/2011

Photo 23 – Highly corroded bolts and segment at left shoulder of ring 147.

Photo 24 – Reduced corrosion (compared to adjacent segments), predominantly on right

shoulder – view looking south from ring 150.

Appendices


25 Printed 23/11/2011

Photo 25 – Reduced corrosion (compared to adjacent segments) on right hand shoulder of ring

150.

Photo 26 – mm stepping between flanges at ring 165.

Appendices


26 Printed 23/11/2011

Photo 27 – mm stepping between flanges at ring 165.

Photo 28 – View to the south from ring 180.

Appendices


27 Printed 23/11/2011

Photo 29 – Build up of stalactites at crown of ring 192

Photo 30 – Reduced corrosion (compared to adjacent segments) in segment at right hand

shoulder of ring 197. Bolts are heavily corroded.

Appendices


28 Printed 23/11/2011

Photo 31 – Heavily corroded bolt at right hand shoulder of ring 197


shoulder bolts. Corrosion around bolts.

Appendices


29 Printed 23/11/2011


shoulder bolts. Corrosion around bolts.

Photo 34 – Left hand shoulder, condensation on cables.

Appendices


30 Printed 23/11/2011

Photo 35 – Reduced corrosion (compared to adjacent segments) on right hand shoulder of ring

234-235

Photo 36 – Reduced corrosion (compared to adjacent segments) on left hand shoulder of ring

234-235 and condensation on cables.

Appendices


31 Printed 23/11/2011

Photo 37 – View south from ring 249 towards south.

Photo 38 – Corrosion on left hand shoulder and crown of ring 270-271

Appendices


32 Printed 23/11/2011

Photo 39 – Corrosion and stalactite build up at ring 272

Photo 40 – Reduced corrosion (compared to adjacent segments) at right hand shoulder of ring

280 to 282

Appendices


33 Printed 23/11/2011

Photo 41 – Corrosion at right hand crown bolts of ring 281.

Photo 42 – Corrosion at right hand crown bolts of ring 281.

Appendices


34 Printed 23/11/2011

Photo 43 – Corrosion at right hand crown bolt of ring 281.

Photo 44 – Corrosion at right hand crown bolt of ring 281.

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

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