The steel pipe that tunnel machine Bertha struck in December wasnt just some scrap that a contractor forgot to remove in 2002 but a crucial piece of equipment that engineers reused as recently as 2010, to learn how groundwater and construction affect each other.
The findings were shared with construction companies during the homestretch of the bidding competition to drill the worlds widest single-bore tunnel.
The pipes location and purpose are described in two documents the state Department of Transportation (DOT) provided to potential bidders, including Seattle Tunnel Partners (STP), which won the $1.44 billion Highway 99 tunnel contract.
Yet somehow, Bertha hit the pipe Dec. 3. Workers removed a 55-foot section that had been pushed upward, and the machine advanced for three more days, until the cutting teeth stopped grabbing soil. Operators turned off the tunnel machine to avoid damaging it.