WSDOT Suspends SR 99 Tunneling Following Sinkhole

The SR 99 TBM has progressed 1,280 ft. (Photo by WSDOT)

The SR 99 TBM progressed 190 ft since re-launching. In total, it has mined 1,280 ft of its approximately 10,000 ft alignment. (Photo by WSDOT)

The Washington State Department of Transportation (WSDOT) has notified Seattle Tunnel Partners, the deign-build contractor for the SR 99 tunnel, that it must stop tunneling operations in the wake of a recent sinkhole that developed along the tunnel alignment.  The sinkhole, which developed on Jan. 12, occurred about 35 ft north of the access pit and 100 ft behind the cutterhead.

Earlier on Jan. 12, a separate incident occurred in which a barge that was used to transport tunnel spoils began to list, resulting in some spoils spilling into Elliott Bay, WSDOT reported.

RELATED: SR 99 TBM Advances Out of Access Pit

The stop order was issued on Jan. 14. According to WSDOT, STP must complete a detailed analysis and modify tunneling operations to ensure appropriate ground control. STP will not be allowed to resume tunneling until their analysis and work plans meet the satisfaction of the design-build contract and WSDOT’s experts.

As of Jan. 12, STP had mined more than 190 ft and installed 30 concrete tunnel rings since the TBM first moved forward in the pit on Dec. 22. This brings the total distance tunneled to 1,280 ft and a total of 188 concrete rings.

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