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Mayor’s response to Thames Tunnel Consultation

Appendix 3 – Crossrail Letter

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0203 229 XXXX

CRL1-XRL-C-COL-CRG03-00001

14th December 2010

Mr Phil Stride Head of London Tideway Tunnels The Point, 7th Floor 37 North Wharf Road Paddington London W2 1AF

Dear Phil,

Crossrail: Response to Thames Tideway Tunnel Public Consultation

The following document is a formal response to your letter of the 10 September 2010, requesting Crossrail Ltd.’s response to the TTT public consultation.

Our response has focussed on the areas where there are likely to be impacts between your proposed scheme and Crossrail (See Appendix I).

Direct impacts and potential Settlement Impacts There is a potential alignment clash at the intersection of the Crossrail and TW (Abbey Mills Branch) route alignments. The location also coincides with the DLR viaduct and Limehouse Link, both of which require assessment of settlement impacts. Crossrail will need assurance that any settlement resulting from this, TTT will be discernable from that of Crossrail, and that it will not impair or increase the cost of delivering Crossrail. The point of interception between Crossrail and the proposed TTT route, at this location, is where Crossrail’s Drive Z will be running.

A further potential impact arises where Crossrail and TTT route alignments cross beneath the Thames, opposite North Woolwich Station, (Crossrail Drive H). Acceptance of TTT alignments is dependent on proximity, timing, geographical features, separation and ground movements caused as a result. Details of which, need to be advised by Thames Water.

Given that the Crossrail tunnel will have been constructed before the TTT, sufficient instrumentation and monitoring within the TTT tunnel and the CRL tunnel to monitor the impact of the construction of TTT will be required.

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TTT would monitor the impacts of their own construction and would need a system for doing this. For any damage caused to the Crossrail tunnel, TTT would need to mitigate and pay for any remedial work that is required.

The other potential impact of settlement caused by the TTT tunnel, is where the settlement troughs under the Crossrail running tunnels cross, have an impact on third party assets on the surface. Wider instrumentation and monitoring should be used in order to differentiate between the impact on the tunnel and third party assets. Crossrail will only be maintaining their settlement monitoring for a further 12 months following project completion.

Finally, Crossrail will also be undertaking various mitigation works on Thames Water utilities impacted by tunnelling and therefore, would expect work on TTT not to interfere with Crossrail programme in respect of these works.

Dewatering Dewatering will be required where shafts are sunk. Crossrail is expected to dewater at a rate of 150L per second for over four years at sites like Limmo, Stepney Green and the drive Y and Z cross passages.

The issue around dewatering concerns the adverse impact on third parties who have dewatering licences to supply water for their business. When the TTT is constructed the issue will be compounded as further dewatering will be required. As the TTT is deeper, it may cause additional loss of water supply.

Existing contamination sites will also require careful monitoring, in the event they are mobilised by modified groundwater flows, the appropriate client will be allocated responsibility for mitigation measures. Dewatering is only likely to be an issue in the East London area.

Logistics There is no immediate evidence of clash or construction interface issues, but Crossrail would expect Thames Water to consult Crossrail as detail develops, in order to avoid interference to Crossrail construction traffic on prescribed routes. Crossrail would expect to be committed on a logistics network (levy routes etc) to ensure minimum impact on project delivery.

Crossrail and TTT have construction sites which are in close vicinity of each other (eg the Crossrail Pudding Mill Lane site and TTT (Abbey Mills Branch)). In such instances we would expect Thames Water to consult Crossrail on their proposed construction arrangements including traffic routes and vehicle numbers to ensure there are no conflicts. This would be in the interest of both parties to ensure the combined impact is not detrimental to London. Furthermore, Crossrail are developing logistics solutions regarding the disposal of excavated material and minimising vehicle movements. These proposals will progress as we start to award the main tunnelling contracts. As Thames Water develop their proposals for these activities the Crossing the Capital Connecting the UK

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two parties should continue to share ideas and solutions to determine whether there are combined benefits to both.

Crossrail Line 2 There doesn’t seem to be any apparent conflict with Crossrail Line 2 – Chelsea Hackney Line (CHL) and the TTT.

An outstanding matter however, is the vertical separation between the CHL and the TTT. We have not yet set a firm level for the CHL below the River, as we have little information on the depth of the River at this point. Until we have this information, we cannot set a tunnel depth and ascertain the vertical clearance between CHL and the TTT. The depth of the river could force CHL closer to the top of the Tideway Tunnel, which may influence the method of construction and any resulting mitigation works. It would be useful to the both parties, if the a copy of the Thames Water log for the borehole close to Chelsea Bridge is provided to Crossrail in order to ascertain a clearer position regarding this point.

I trust this is satisfactory as an initial assessment of the potential impacts caused as a result of the proposed TTT. As the TTT scheme develops, including preferred option selection, a further assessment will be required by Crossrail, to ensure that potential impacts are mitigated where necessary. .

Yours faithfully,

Sanjay Patel Head of Utilities Management Crossrail Limited

c.c. Clinton Leeks, Andy Mitchell, Chris Sexton

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Appendix I – Crossrail and TTT Route Alignment

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