Owner
Sound Transit
Client
Jacobs Engineering
Cost
$4.9 billion USD to $5.3 billion USD
Timeframe
April 2025
— December 2032
Services performed
During planning phase 1 DSP prepared the preliminary engineering design of the TBM starter tunnels, of cross passages every 800 feet, and temporary and permanent support of excavation of the Alaska Junction Station. Phase 1 services included further early works design, value engineering, cost saving analysis, and cost estimates. Planning phase 2 of the project will anticipate the preparation of the final design of said structures.
Description
The West Seattle Link Extension (WSLE) is part of Sound Transit’s regional transit system expansion and will add 4.1 miles of light rail, a new bridge, tunnel and three new stations at SODO, Delridge, and Alaska Junction, connecting Seattle's SODO neighbourhood with West Seattle's Alaska Junction neighbourhood. WSLE will improve regional mobility by increasing connectivity and capacity to Downtown Seattle to meet the projected transit demand.
Geology
Glacial and nonglacial deposits, with layers of till, cohesionless sand / gravel, cohesionless silt / sand and cohesive clay / silt. The project site is in an area of high seismicity. Geologic hazards include landslides, fault rupture, liquefaction and lateral spreading.
Location
Seattle, WA, USA
Highlights
- TBM Starter Tunnel in SEM, temporary & permanent SOE for station box, and cross passage design in soft ground.
- Area of high seismicity and geologic hazards such as liquefaction.
- Cost saving design.
West Seattle Link Extension (Source: Sound Transit)
TBM Starter Tunnels Cross Section including cross passage - Planning Phase 1