Snaresbrook Embankment Stabilisation Project

Project team: Metronet & Trans4m: Alliance, Cementation Foundations Skanska

Metronet Rail, in partnership with London Underground, has been revitalising and upgrading two thirds of the Tube. Part of this work involves strengthening and repairing embankments, including one between Snaresbrook and South Woodford stations located at the eastern end of the Central line in Wanstead, East London.

The 100-year-old embankments along this stretch of the Central line had deteriorated over the years and the works were required to make them more stable. The Project was undertaken by Metronet & Trans4m alliance, with Cementation Foundations Skanska responsible for the design and build contract. The CEEQUAL assessment was conducted by Atkins.

The Snaresbrook Embankment Stabilisation Project was conducted between the station bridge adjacent to Snaresbrook Station and the subway at the end of Falcon Way. Works were undertaken on the westbound embankment slope, which is situated behind residential gardens off Sylvan Road, and behind Trafalgar Place.

The site was identified as being in need of remedial stabilisation works, which then took place between November 2004 and July 2005. Large parts of the upper portion of the embankment showed bare areas, where loose ash-fill surfaces were exposed and were actively ravelling down the slope. This was causing crest stability problems which, in turn, had undermined support to both the line-side services and track. After an analysis of options, it was concluded that the preferred solution would be to construct a bored pile retaining structure along the central areas of the embankment, with localised earthwork berms at either end of the site

Environmental management

Metronet & Trans4m alliance is ISO 14001-registered and all projects are carried out under the organisation’s environmental management system. Hence, the principles of effective environmental management were applied throughout this project. The project team included a dedicated environmental manager who provided ongoing support and guidance to the project manager.

The project team showed its commitment to environmental protection from the start, as other solutions that would have involved extensive vegetation and tree removal and a large amount of night-time working were rejected.

Ecology & landscaping

In order to conduct the essential stabilisation works, it was necessary to remove some existing trees and vegetation from the embankment. Ecology and landscaping were therefore key environmental concerns for this project.

There was full consultation with the London Borough of Redbridge, and comprehensive ecological surveys were conducted to identify any protected flora and fauna. Moreover, when nesting birds were discovered earlier than anticipated in the initial survey, the whole project was postponed by over six months. No other protected species were identified on site. Nevertheless, a Metronet & Trans4m alliance ecologist was involved to ensure any potential issues could be managed effectively.

Wherever possible, existing trees were retained, with both the construction scaffolding platforms and the final structure re-designed to maximise tree retention. A replanting programme is now underway to reduce the visual impact of the repair works

Community liaison

The other key issue for this project was disruption to local residents, which was managed with a high degree of consideration and sensitivity by Metronet & Trans4m alliance. The embankment backed onto some local residents’ gardens and properties, and hence some degree of disturbance was unavoidable.

However, thanks to an extensive community relations programme, which included press releases, letter drops and face-to-face liaison, the project was received well by the local community. A Metronet Rail Exhibition bus visited the site to help promote awareness of the works and to answer any queries from local residents and community representatives, including the Mayor of Redbridge and the MP for Ilford North.

With works completed, the project team was keen to leave a positive impression and, by laying a new road surface, clearing rubbish and erecting a new fence on land which they had used as their site compound, they were able to leave the area in a better condition than before the works, much to the delight of local residents.