Two tunnel collapses have hindered operations on the US$12bn Taiwan High Speed Rail Link in the past month, both on the 4.3km Hokou tunnel in Taoyuan county. Nobody was injured.
Contract C215 (that involves construction of part of the Hokou tunnel and Taoyuan station) suffered what is understood to be a 100m3 collapse at the beginning of December 2002. This preceded a second smaller fall about two weeks later on C210, the contract for the rest of the tunnel which is being constructed in conjunction with C215.
Contractor, Obayashi/Futsu JV, has halted construction and is investigating the collapse with the client, the Taiwan High-Speed Rail Corporation, and its consultants.
The geology along the alignment has been well-documented, with excessive hydrostatic conditions carefully monitored in some tunnels.
The tunnels are being mined using the sequential excavation and support method. Temporary support was achieved with rock bolts from the spring line to the crown, lattice girders spaced 1m-1.5m apart, and shotcrete ranging from 175mm to 350mm thick. The final tunnel lining is typically a reinforced concrete shell designed to support the tunnel without the benefit of the temporary lining.
