C435 Crossrail Farringdon Station

Tunnelling works at the Crossrail Farringdon Station in central London are underway; the majority of the sprayed concrete lining (SCL) tunnels are completed. Almost 90% of the Westbound and Eastbound platform tunnels, both 300 metres long with a tunnel axis at a depth of approximately 30 metres below street level, have been constructed. Furthermore multiple cross passages and two stub tunnels for the reception of the two Earth Pressure Balanced (EPB) Tunnel Boring Machines (TBMs) arriving from the East have been completed.

The station is being constructed in diverse ground conditions due to the presence of several faults and the heterogeneous Lambeth Group. The challenge of excavating through varied ground conditions required the implementation of temporary works contingency measures and in-tunnel depressurisation to alleviate the water-bearing sand channels of the Lambeth Group. Especially during the excavation of the Eastbound platform tunnel, a combination of dewatering, grout injections, grouted spiles installation and pocket excavation were implemented. Thus a 30m long, water bearing sand lens located at the crown could be sucessfully excavated.

A thorough daily in-tunnel and surface monitoring process is in place to ensure the safety of the SCL works and protect party assets.

At present, the SCL works are focused on the excavation of the western escalator shaft, while underground preparation works for the arrival of the two remaining TBMs, Elisabeth and Victoria, are on-going.

Secondary lining works are concurrently in progress, with installation of the sheet waterproofing membrane and in situ casting of the invert concrete.

The Dr. Sauer & Partners team is providing 24/7 site supervision support to the Bam Nuttall, Ferrovial Agroman and Kier Joint venture (BFK) until the completion of the SCL tunnelling works. These are scheduled to be completed later in 2015.