University Link extends the existing light rail service from Capitol Hill to downtown Seattle and the airport. The twin precast concrete segment tunnels are approximately 3,800 ft. each and were excavated via earth pressure balance tunnel boring machine (EPBTBM). The tunnel depths range from more than 130 ft. to less than 18 ft. where it crosses Interstate I-5, the major north-south artery in Seattle. Nearly the entire tunnel alignment consisted of horizontal & vertical curves with the tightest curve radius being only 550 ft. Five cross passages that connect the twin tunnels were constructed utilizing the sequential excavation method (SEM).
The Capitol Hill Station (CHS) shaft excavation was 540 ft. long x 80 ft. wide x 80 ft. deep. The ground support utilized was a combination of soldier piles and lagging supported, tiebacks, shotcrete and soil nails. The CHS shaft excavation also includes the construction of a concrete base slab for the future subway station. This base slab is 8 ft. thick and required placing approximately 12,000 cy. of concrete.
