The Thameslink Hornsey depot, which is expected to be completed in 2016, is being constructed within a live operational rail environment adjacent to the East Coast mainline and the existing Hornsey depot.
The project comprises the co-ordinated redevelopment of two separate areas of existing infrastructure, including the existing operational depot and the derelict sidings immediately to the north of the existing depot. The work involves the widening of two existing bridges, a new three road, 12-car maintenance shed, two carriage washing machines, offices and all associated depot infrastructure. Alterations to the existing depot are being undertaken in close consultation with the train operating company to minimise disruption throughout the project.
The main contractor for the works is VolkerFitzpatrick. In order to create the footprint for the access road and car parking to the south of the new depot building, VolkerGround Engineering were appointed to install a steel sheet pile retaining wall at the top of the existing embankment. The total length of wall installed was 321linm, 258m of AZ36-700 sheet piles at 15m and 63m of AZ28,700 piles 14m long. The structure was located along the site boundary at the top of the existing slope with piles driven to a designed reduced level through the embankment made ground and into the underlying London clay.
To drive the sheet piles into the stiff clay, VolkerGround Engineering utilised an ABI 16/20 hydraulic leader rig which pre drilled stronger areas of the material with a 300mm diameter Continuous Flight Auger attachment and then drove piles to practical refusal with the rig's vibratory hammer. Where required piles were back driven with a crane suspended SL 30 hydraulic impact hammer to the required embedment depth.