130km of tunnels on US rail link
20 February 2003The North American state of California is currently conducting an Environmental Impact Report (EIR)/ Environmental Impact Statement (EIS) for the construction of a 1,127km long high-speed rail link running from San Diego in the south to Sacramento and San Francisco in the north, which will be published in August 2003.
Alignments under consideration require a total of over 130km of twin-tube tunnelling, with some individual tunnels stretching more than 48km. Crossing the Tehachapi mountains between Los Angeles and Bakersfield could require up to 72km of tunnelling.
The proposed route traverses terrain with challenging tunnelling conditions. Kip Field, project manager with Parsons Brinckerhoff, told T&TI that the engineers expect hard and fractured rock, high pressure ground water, oil and gas deposits, and difficult seismic conditions – including faults with lateral displacements of up to 20m.
Numerous studies and reports have already been published on the viability of the project, with interest already being shown by DMJM & Harris, Hatch Mott MacDonald, Shea Construction and Obayashi.
In September 2002, the first US$9.95bn was promised to the California High Speed Rail Authority, by Governor Gray Davis, who said "every major population centre in the state will benefit". The General Obligation Bond will be placed on the November 2004 ballot. The total cost of the project is expected to be in the region of US$25bn.
The studies and reports already agree on some aspects of the associated tunnelling works. TBMs are the expected excavation method, as they require less construction time than drill and blast. On tunnels longer than 10km, a third tunnel should be built for ventilation, evacuation and construction access, and all tunnels should be lined for structural, water-tightness and aerodynamic reasons.
Parsons Brinckerhoff is the lead company in the programme management team, responsible for setting engineering and tunnelling criteria. The schedule for works will follow the publication of the EIR/EIS.
