Tunnel - South Interceptor Parallel

King County, WA

This 2,500 foot long portion of the underground sewer line was originally designed to be constructed of precast jacked pipe. Subsurface conditions were not favorable for that tunneling method and Sehulster Tunnels, Inc. was approached by the contractor to submit an alternate design for a bolted-gasketed precast segment lining. 

The alternate proved to be more economical and 3,750 precast segments were fabricated and shipped to the jobsite. These were assembled into rings underground by the tunnel boring machine as it excavated the tunnel . The 625 rings, each 4 feet long and 9 feet in diameter were left behind as the final waterproof liner while the tunnel boring machine continued along its path, excavating and removing material from the hole.


  • Precast Tunnel Liner Segments - 3,750 pieces


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