Shallow TBM launch of the Northolt Tunnel West TBMs at West Ruislip

Abstract Launching tunnel boring machines (TBMs) from a station box or launch shaft is a delicate operation that requires careful planning to maintain safety. Seven TBMs excavate the tunnels on the southern section of the High Speed Two (HS2) Phase One route and will bore an approximately 23km twin tunnel connecting Euston Station in London, Old Oak Common in North Acton and West Ruislip. Three out of seven TBMs are set to be launched in very special conditions due to shallow alignment constraints. This paper describes the structural and geotechnical works designed for the West Ruislip area, where two TBMs will start the bore of the HS2 Northolt Tunnel West (NTW). These works include extensive piling, civils, ground treatment and soil works. The innovative method described in this paper and its implementation in the HS2 Project promote confidence in economic and environmentally sustainable technical solutions with a minimum carbon footprint.