U230 Light Rail Capitol Hill Station – Utility Support Beams and Temporary Construction Bridge, Sound Transit
CivilTech designed temporary utility support beams to span the excavation pit required for the Capital Hill Station. The underground station required excavating 540’ by 56’ by 75’ deep to install the tunnel structure. Existing utilities in the area include a 16” diameter gas line, 115kVA electrical line encased in an 8” steel pipe, 12” diameter water line, 10 fiber optic conduits, and two 5” diameter Comcast conduits. The existing utilities were suspended from the utility support beams to straddle the excavation pit. The support beams were designed as single span structures with a deflection limit of l/360. CivilTech also designed a temporary haul bridge to provide access across the excavation pit for construction equipment and traffic. The 67’ long by 28’ wide bridge consisted of WSDOT standard precast prestressed voided concrete slabs with a 3” non-composite concrete topping slab. The bridge was founded on cast-in-place piles at each end to avoid exerting excessive lateral loading on the adjacent soldier pile shoring walls.