University Link Light Rail, Contract U230 is a component of the 3.15-mi light rail extension that will connect downtown Seattle with the University of Washington campus. The project includes construction of 0.75 mi of twin tube metro tunnels and associated cross passages, excavation and support of the Capitol Hill Station structure, and excavation of a TBM retrieval shaft at the Pine Street Station. The tunnels are approximately 19.3 ft in diameter and are being excavated through a range of overconsolidated fine- and coarse-grained materials using an earth pressure balance TBM.
Lachel was retained by the contractor (JCM U-Link, JV) to provide independent geotechnical and tunnel engineering services for the project. For the running tunnel construction, Lachel was tasked with structural design of the precast concrete segmental tunnel liner. The design included critical analysis of governing ground and hydrostatic loads, and construction loads such as handling, jacking and grouting pressures. Forces in the lining were assessed using two- and three-dimensional structural analysis software, and reinforcement quantities and arrangement were determined. Segment gaskets, bolts, and connector systems were evaluated; and all required calculations, analysis, drawings, and details were packaged for contractor submittal.
Lachel 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, Lachel 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.