Sound Transit Beacon Hill TBM

In early July the Mitsubishi TBM for the Beacon Hill contract arrived in Seattle on a container ship from Kobe, Japan.

The arrival of the 327t machine was a milestone in the construction programme for Sound Transit's 22.5km long Central Link Light Rail (CLLR) project a third of which will be tunnelled (T&TI, February, p10). The Beacon Hill scope involves a deep station complex and two new running tunnels 1.3km and 1.29km long excluding the platforms. The tunnels are to be driven to a 5.7m finished i.d. through glacial soil varying between fine grained silt to clay and boulders.

The 6.44m diameter Mitsubishi EPB machine will drive the first tunnel from west to east and then be turned to excavate the return drive. Contractor for the contract is Obayashi Corporation, who now has to transport more than 30 truckloads of TBM components from the port to the west tunnel portal for assembly. T&TI was told work on the first tunnel should be underway by September this year, with an advance rate of 12m per day expected.

Also in July, Sound Transit chief executive officer, Joni Earl, recommended to the board that the First Hill underground station be dropped from the agency's extension to Husky Stadium. The reasons given were that poor soils would mean the tunnel would have to be built 64m underground, which would eliminate conventional tunnelling methods, as well as funding concerns. T&TI was told the Sound Transit board voted in favour of Earl's recommendations by 12-1 to revise the route and eliminate the station.

With the final environmental impacts still underway and final decisions on planned routes not expected until later this year, there is still hope for the station to be included in the plans in a modified form. Currently decisions are being based on who and how to apply for funding, but it is believed a motion may be put before Sound Transit's board to assess alternative construction methods or locations for the station.