Tunnel - Mercer Street CSO

Seattle, WA

The precast tunnel liner segments are used for a single-pass, bored concrete tunnel that is located approximately under Mercer Street in Seattle and extends from Lake Union to Elliot Bay. The 14'-8" diameter tunnel is a combined sewer overflow (CSO) facility that can store up to 7 million gallons of storm water during peak demands before releasing it back into the sewer system for treatment. 

The liner system is composed of 1550 rings, 4 ft. long x 14'-8" i.d. and 9" thick. Each ring is segmented into 6 precast curved panels. The circumferential and radial joints between segments are bolted or pinned and gasketed to form a watertight seal as they are installed by the tunnel boring machine. 

The need for a watertight final fit dictates exacting dimensional tolerances for these products.


Precast Tunnel Liner Segments - 9300 pieces


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