Tunnel boring has been halted at Beacon Hill rail station in Seattle to await the outcome of investigations into a fatal supply train crash in early February.
All construction work was initially stopped on the Obayashi contract following the accident at the west portal to the underground works on 7 February. Excavation work inside the station and construction at the east portal were cleared to restart within two days.
The TBM in the southbound bore is at a standstill. Excavation will not be allowed to restart until regulatory agencies investigating the accident have released the site, which is at the logistical supply hub of the tunnelling works.
The fatal accident happened when a loaded supply train emerged from the west portal and collided with a stationary loco. One of the two workers on the moving train died, but it wasn’t known if the major injuries he suffered were caused directly by the collision or if he fell or jumped from the loco. The other worker, the loco operator, was onboard throughout the incident and suffered minor injuries.
Contractor Obayashi expressed regret at the tragic accident and said it would work with local authorities to determine the cause of the crash, but declined to give further comment.
A train accident happened at the west portal late last October, when brakes failed and workers jumped well before the loco broke through the rail stop, a guardrail, and over a wall, to fall to an access road below. They escaped with minor injuries. The train system had been subject to an investigation following the accident, which produced a safety audit in mid-January to which the contractor was to respond by 7 Feb (the day of the second accident). The deadline was extended by a week.
Obayashi had only re-launched the Mitsubishi EPB TBM in mid-December. The machine had waited for station excavations to progress enough to let it be taken through the cavern and continue the southbound bore (T&TI, January 2007, p8).
*Also in Seattle, further developments on the options to replace the Alaskan Way Viaduct saw a slimmer ‘hybrid’ tunnel option appear, pushed by the city council.
Balking at the estimated US$4.6bn cost of the original proposal worked up by the state for a six-lane cut and cover tunnel, the council advocated a smaller, four-lane US$3.4bn tunnel to help reduce the gap on the US$2.8bn quote for a replacement elevated structure.
Washington’s State Governor, Christine Gregoire, wanted voters to choose between the options of a six-lane tunnel versus the much cheaper replacement structure.
