University Link Light Rail Contract U230

Connecting downtown Seattle with one of the oldest universities on the West Coast, the University Link Light Rail, Contract U230, project was a component of the 3.15 mile light rail extension that linked the downtown area with the University of Washington campus. Schnabel was retained by the contractor (JCM U-Link joint venture) to provide independent geotechnical and tunnel engineering services.

The project included the construction of .75 mile of twin tube metro tunnels and associated cross passages, excavation, and support of the Capitol Hill Station structure, as well as excavation of a tunnel-boring machine (TBM) retrieval shaft at the Pine Street Station. The 19.3-ft diameter tunnels were excavated through a range of over-consolidated fine- and coarse-grained materials using an earth pressure balance TBM.

For the running tunnel construction, we were tasked with the structural design of the precast concrete segmental tunnel liner. Our design included critical analysis of governing ground and hydrostatic loads, and construction loads such as handling, jacking, and grouting pressures. We assessed forces in the lining using 2-D and 3-D structural analysis software to determine reinforcement quantities and arrangement. Segment gaskets, bolts, and connector systems were evaluated, and all required calculations, analysis, drawings, and details were packaged for contractor submittal.

We also assisted the contractor with value engineering proposals and provided additional design services related to welded and bolted structural connections of temporary excavation support systems. For the Capitol Hill Station construction, our field staff monitored the installation and testing of more than 1,500 structural elements (soldier piles, tie back anchors, and soil nails) used in the support of the 400-ft-long, 50-ft-wide, 60-ft-deep station excavation.