The soil around tunnel-boring machine Bertha pushed upward after groundwater flows were restored, but the project remains stalled. Structural experts found no major damage to buildings, said an official with the Highway 99 tunnel project.
The soil around tunnel-boring machine Bertha rose upward three-fifths of an inch after normal groundwater flows were restored last month.
“Some of the Alaskan Way Viaduct columns and buildings show similar movement,” says an update Friday by the Washington State Department of Transportation (WSDOT).
However, structural experts found no damage to building foundations, said Dave Sowers, deputy program administrator for the Highway 99 tunnel project.
This surge of three-fifths of an inch represents a partial rebound, Sowers said, after the ground settled up to 1¼ inches during previous groundwater removal.
“This is somewhat expected,” he said.
Ground surges occurred mainly between the waterfront and Second Avenue, and from South Washington Street to South King Street.
In November 2014, four deep wells were removing as much as 800 gallons per minute to reduce the pressure against Bertha’s 120-foot-deep repair access vault. Otherwise, groundwater at up to four times atmospheric pressure could have leaked into the vault or endangered workers by blowing up through the vault floor.
Settlement related to rapid groundwater removal was suspected of damaging an old city water main, now being replaced under Western Avenue. Other construction in the area could be a factor, state experts say. Structural inspectors found no building foundations damaged, though property owners did file four claims for lesser damage.
Since then, the machine’s 4 million-pound front end was lifted to street level, strengthened and reattached.
Gov. Jay Inslee and the WSDOT suspended drilling Jan. 14, two days after a sinkhole of 250 cubic yards formed near South Main Street, in a spot where Bertha’s rotary cutterhead had passed through.
Chris Dixon, project manager for Seattle Tunnel Partners (STP), has called the stoppage “wrongful and unjustified,” and said Bertha should immediately resume drilling 250 more feet, until it reaches a concrete-lined rest stop near the Viaduct.
Inslee’s staff say it’s unsafe for drilling to proceed until STP shows how it can properly manage the rate of soil removal.
The dispute might add weeks to a schedule that already slipped from a December 2015 grand opening until April 2018, for traffic to enter the four-lane tolled tunnel that will link Sodo and South Lake Union.
Sowers declined to speculate on when drilling might resume, or comment about whether the frayed relationship between the state and its contractors is mending.
“All I could say is we’ve got a lot of good people trying to reconcile these issues,” Sowers said.
Meanwhile, contractors have received permits to repair damage at Terminal 46, where a barge carrying tunnel soil tilted Jan. 12 and dislodged at least 15 vertical pilings that protect the dock.
And at the project’s north end, the first phase of sign construction work was finished a week early in the median of Aurora Avenue North — so the southbound bus-only lane into downtown reopened Friday afternoon, except for one block at Comstock Street, spokeswoman Laura Newborn said.