Sound Transit is seeking international interest in the Beacon Hill project in Seattle, US. It anticipates overseas contractors partnering with American companies to offer speciality experience.
There will be a two-step procurement process for the Beacon Hill tunnel contract, which includes the Beacon Hill station and tunnels, and an adjacent aerial station. A ‘request for qualifications’ will be issued at the end of this month, followed by bid-invitations to pre-qualified contractors.
The 1.3km long Beacon Hill tunnel is part of the Central Link light rail line. The underground Beacon Hill station, will be one of 11 stations planned for the 22.5km long initial segment.
The running tunnels will be mined by EPB TBMs, while the station will be constructed by the Sequential Excavation Method (SEM), similar in many ways to NATM. A 15m diameter main shaft will house the elevators, providing access to the twin 122m long platform tunnels. Both the main shaft and the 9m diameter ancillary shaft will house emergency stairs as well as tunnel and station ventilation systems. An exploratory test shaft was recently excavated in this location to gain a better understanding of the complex glacial soils and groundwater conditions (see photograph).
Data gathered from the test shaft will be used in completing the design and will be incorporated into contract documents (prepared by Hatch Mott MacDonald).
The shaft provided information that could not be obtained from traditional soil borings. Based on the results, the designers, and a review committee, recommended that the means and methods of constructing the shaft’s initial support be adjusted in order to stabilise the soils before installing the permanent structures. For example, slurry walls should be used as initial support for the main and ancillary shafts instead of the planned SEM.
Tunnelling engineers are invited for a presentation and a tour of the site, on 11 and 12 November 2003.
Contact John Carpenter, on +1 206 398 5149 or carpenterj@soundtransit.org for details.
