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Seattle Tunnel Status: On Again

Wednesday, March 2, 2016

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Six weeks after a sinkhole halted excavation of the new State Route 99 tunnel in Seattle, the design-build firm in charge of digging the underground portion of the Alaskan Way Viaduct Replacement Project has received “conditional permission” to resume operations.

Seattle Tunnel Partners picked up tunneling operations Feb. 23 after the Washington State Department of Transportation conditionally lifted the “suspension for cause” it issued Jan. 14, halting boring and barging-related activities following two safety incidents, the agency announced in a statement.

The most recent project delay came after the drilling machine nicknamed "Bertha," which had been was taken out of service for repairs in 2013, had just returned to work on Dec. 22. Reports indicate that Bertha had dug only about 150 feet when digging stopped again on Jan. 12.

Conditions of Resuming Work

As part of the conditions for lifting the suspension for cause, STP will be permitted to tunnel forward a short distance and install approximately 25 concrete tunnel rings, according to WSDOT.

SR 99 Tunnel Progress, WSDOT
Photos: WSDOT unless otherwise specified

Seattle Tunnel Partners picked up tunneling operations Feb. 23 after WSDOT conditionally lifted its Jan. 14 “suspension for cause,” halting boring and barging-related activities following two safety incidents.

During this time, the company must demonstrate that they have instituted safety measures that they can safely continue mining. These changes include:

  • Updated tunnel work and quality plans, including calculations of the amount of soil removed during excavation of each tunnel ring;
  • Realignment of key personnel within their quality assurance program;
  • New quality assurance protocols;
  • New personnel at key positions within the tunneling operation; and
  • Restructured daily tunneling meetings that include additional participants and protocols.  

WSDOT made the decision to conditionally lift the suspension for cause after its tunneling experts evaluated documentation submitted by STP over the past several weeks.

“WSDOT, in consultation with its team of tunnel experts, lifted the suspension of tunneling for cause and said that conditional tunneling should resume for 25 more tunnel rings,” said Washington Gov. Jay Inslee. “I concur with their decision, and WSDOT has notified the contractor,” said Inslee.

“The contractor has a plan for modifying tunnel operations to ensure positive ground control,” he explained. “It has also made changes to key personnel, and it has put in place protocols for quality control and assurance. The contractor now has an opportunity to show progress during this test period, prior to tunneling under the viaduct and underneath Seattle.”

While digging can resume, use of barges to haul away excavated material will remain restricted until additional documentation is received.

As a result, STP will remove excavated soil by truck while addressing the barging issue.

Conditional Lift Period

The boring machine, currently located west of the Alaskan Way Viaduct, will be permitted to tunnel ahead approximately 160 feet as part of STP’s initial testing phase.

If STP demonstrates that their revised mining procedures are effective, crews will continue to move an additional 100 feet north to a planned maintenance stop.

Once there, crews could spend several weeks performing final maintenance before the machine tunnels beneath the Alaskan Way Viaduct.

Conveyor / WSDOT

During the Jan. 12 barge incident, STP workers feared the listing barge would damage the conveyor system, part of which is shown here, used to transport dirt from Bertha's digging site to the barges to be hauled away.

WSDOT will fully close SR 99 through downtown for approximately two weeks while the machine passes beneath the viaduct. The closure date will depend on the tunneling machine’s progress.

Unsafe Conditions

Work was suspended for cause on Jan. 14 per section 14.2 of the project contract, which specifies the state can suspend work without liability to WSDOT under a number of conditions, including the contractor’s failure to “correct conditions unsafe for the project personnel or general public,” WSDOT indicated.

In the suspension for cause document supplied to STP, WSDOT indicated that the contractor had failed to correct unsafe conditions affecting project personnel or general public.

At that time, WSDOT asked STP to confirm the following before tunneling could resume:

  • The tunneling machine is operating as intended and meets the design-build contract’s technical requirements;
  • All necessary training for staff on the tunneling machine is complete;
  • The tunneling work plan is updated to address the over-excavation that led to the sinkhole;
  • Processes are in place to ensure STP’s tunneling work plan is followed; and
  • STP updates its quality program to ensure key quality program managers are involved in all tunneling activities.

The specific series of events leading to the stoppage included discovery of a sinkhole over the tunnel on Jan. 12, as well as a barge that listed “beyond STP’s control” at the filling operation that same day, according to WSDOT.

Sinkhole Discovery

At the time, STP said the 35-foot-wide sinkhole would not be “dire” to the project, as reported earlier.

“The sinkhole is an unfortunate event, but isn’t something that is unique or something that wasn’t anticipated,” STP project manager Chris Dixon told the Seattle Post-Intelligencer.

Dixon went on to say that the walls built in the ground to isolate the tunnel from the viaduct during the shallow portion of the dig protected the viaduct from issues around the tunnel, such as the sinkhole.

However, he could not provide a cause for the sinkhole. He told the PI that the group would manually check soil samples moving forward.

WSDOT required STP to provide a detailed analysis and modify tunneling operations to ensure appropriate ground control. The contractor was not permitted to resume tunneling until its documentation and work plans met the satisfaction of the design-build contract and WSDOT’s experts.

Loose, Listing Barge

The barge incident took place as crews were loading it early Jan. 12. When the barge began to lean over, the STP crew released it from its moorings at Terminal 46 in order to prevent damage to the conveyor system, WSDOT reported.

The agency acknowledged that some excavated clean soils were spilled into Elliott Bay before the barge drifted into nearby Pier 48, which is owned by WSDOT and slated for demolition damaging both the terminal and the pier.

In addition to the unpermitted spill of material, the incident posed a hazard to project personnel and the public, the agency noted.

As STP divers and marine surveyors inspected the Terminal 46 damage, crews also assessed necessary steps to ensure safe staging of a barge to load excavations at Terminal 46. Repairs to the pier were completed earlier in February. 

Project Background

As reported previously, the replacement project focuses on the 2-mile-long elevated double-deck road originally built in the 1950s. Damage from a 6.8 magnitude earthquake in 2001 led to the need to stabilize and repair the structure and restrict heavy vehicle traffic.

Most of the existing bridge deck has been replaced with new roads, and the viaduct itself will be replaced by the tunnel.

The 1.7-mile-long tunnel is expected to boast an inside diameter of 52 feet (15.8 meters), allowing it to hold the planned double-deck roadway.

The suspension for cause only addressed tunneling operations involving the boring machine and the loading of barges at the site, WSDOT said. It did not apply to the other ongoing work under the design-build contract with STP or any other contracts being managed by the viaduct program, it added.


Tagged categories: Accidents; Asia Pacific; Department of Transportation (DOT); EMEA (Europe, Middle East and Africa); Infrastructure; Latin America; North America; Program/Project Management; Roads/Highways; Transportation; Tunnel

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