Engineering challenges on the East London Line

From May last year, Tony Gee and Partners (TGP) has been working with Balfour Beatty Carillion Joint Venture providing design services for key sections of the Phase 1 renewal and extension of the East London Line project being developed by Transport for London.

Since the closure of the line at the beginning of this year, much of the work has centred around the central underground section between Whitechapel in the north and Surrey Quays to the south. The section includes an interface with future Crossrail development at Whitechapel, the Thames tunnel between Wapping and Rotherhithe and an interchange at Canada Water.

This original section of the line was built around 150 years ago, designed by Brunel with the river crossing originally developed by Brunel’s father. The tunnels run through London Clay and water bearing gravels and were subjected to both constructive and destructive modifications during the last war. The work in these sections involves upgrading the stations to modern standards incorporating secondary means of escape, fire hydrants and modern fire systems as well as renewal of mechanical and electrical installations such as passenger lifts and traction supply.

Further to the south major works are being carried out at New Cross Gate where the main servicing depot is currently under construction. The depot is being built on a constricted site which is combined with a new grade separated junction creating complex logistical problems for Balfour Beatty Carillion Joint Venture.

The depot has a substantial four road 100m long maintenance building, a wheel lathe and heavy cleaning building and a carriage wash along with stabling facilities for 20 trains. The facilities are specifically designed to meet the requirements for the new Bombardier Class 378 trains being built in Derby. TGP was appointed by Balfour Beatty Carillion Joint Venture to prepare the detailed design for the depot in May last year and construction is now well advanced. The site also includes the operational building complex and Surrey Canal Road substation resulting in highly complex services routing throughout the site. The site is also bisected by Coldblow Lane tunnel which restricts drainage and services across the site.

Further to the south, TGP has recently commenced the design for the new grade separated junction at Silwood providing the connection between the East London Line and the South London Line to Clapham Junction which will be constructed under phase 2 of the project. The grade separation is to be constructed as a dive under and presents complex problems with a potentially high water table and contaminated ground. Stage two site investigation works are currently in progress.

Whilst these two major elements of the project have complex challenges, the central underground sections present some unique engineering problems. These have been developed through early scoping and preliminary design by TfL’s engineers and have been passed to BBCJV’s design managers for detailed design by TGP. One example of this is the Crossrail route protection works at Whitechapel where substantial foundations are required to be incorporated to facilitate a future construction deck for extended station facilities alongside the East London Line.

Another is the installation of the secondary means of escape stairways at Wapping which have to be constructed alongside the station vent shaft retaining wall through water bearing gravels just a few metres from the river. These shafts are then to be connected at low level through the existing retaining walls to the station platforms. The existing cast iron props supporting the retaining walls have been found to be under strength and are being replaced at the same time as the shaft installation following a strictly controlled sequence.

Teamwork amongst the various engineering groups within TGP, BBCJV and TfL is an essential part of this project with design, approval, assurance and construction processes running concurrently with integration across the multi-disciplined environment.

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