September 19, 2014

'A lot of great work is underway' in the tunnel; you just can't see it

Photos by Jon Silver [enlarge]

The machine had burrowed only about 1,000 feet of its 1.7-mile path when it got stuck last December.

[enlarge]

Powerful hydraulic rams called thrust jacks push off completed segments to drive Bertha forward.

[enlarge]

Bertha’s control panel includes a target that helps keep the machine centered as it digs.

Bertha may be out of commission until at least March, but the Washington State Department of Transportation wants you to know that work on the $2 billion state Route 99 tunnel hasn't stopped.

The agency values the work at $750 million, including the construction of roads and infrastructure for the tunnel.

More than 230 workers are on the job at the south tunnel site, west of Seattle's stadiums, according to Chris Dixon, project manager for the contracting team Seattle Tunnel Partners. Fifty-eight of those people are working on Bertha, the tunnel boring machine.

Bertha stalled in December 2013 after damage to the machine's seal system was discovered. The machine had burrowed only about 1,000 feet of its 1.7-mile tunnel path.

Seattle Tunnel Partners is juggling the construction schedule to complete as much work as it can while the repairs are underway.

During a tour on Thursday, Dixon pointed out new infrastructure that is getting built far ahead of original plans. Crews were busy installing concrete corbels — they look like giant steps — along either side of the 52-foot-diameter tunnel interior to support what will become the upper road deck that carries southbound traffic.

Utilities such as electrical and fire-suppression systems were also being installed.

South of the tunnel, several hundred feet of double-decker roadway has been completed, running just short of where it will meet the existing highway.

Inside the 80-foot-deep launch pit, crews were encasing walls with shotcrete for waterproofing. The water table rises to just 9 feet below the surface, said Matthew Preedy, deputy program administrator for WSDOT.

Payoff for this advance work will come at the end when STP can make up time lost to the Bertha repairs. The contracting team hopes to recover as much as five months of its schedule to meet the November 2016 tunnel opening date set by WSDOT.

The tour took reporters deep into the bowels of the 326-foot-long boring machine, which was crowded with tight stairways and mechanical equipment.

Powerful hydraulic rams called thrust jacks push off completed tunnel liner segments to drive Bertha forward into the ground as it mines. Conveyor belts carry out soil and rocks along the length of the tunnel. By the end of the project, the conveyor belt will have grown to 9,000 feet in length.

As the machine pushes forward, 10-piece concrete rings are installed behind it, each segment about 2 feet thick, 6.5-feet wide and 17.5 feet long. Segment widths actually vary a few inches so the tunnel can make gentle turns along its route.

Nearly 1,450 rings will be installed along the length of the tunnel.

Bertha's high-tech operating room sits along an ordinary-looking corridor lined with windowed meeting spaces. One room has a sign exhorting crews to keep a positive attitude.

Dixon said workers assigned to Bertha are busy maintaining equipment and making modifications to improve the machine's performance as needed. He explained various buttons and screens on the control panel, including a target that helps keep the machine centered as it digs.

The din of mechanical equipment was relatively muted in the operations room, and Dixon said it doesn't get much louder in there when drilling happens less than 60 feet away.

Back in an office trailer after the tour, Preedy from WSDOT said drivers whizzing by on SR 99 wouldn't know from the looks of things that so much activity is taking place underground.

At a time when the tunnel project is facing bad publicity after its stumbling start, WSDOT wants to assure taxpayers that progress continues, even amid calls to pull the plug on the whole thing.

“This contractor is committed to finishing the work,” Preedy said of STP. “A lot of great work is underway.”