ROADS/BRIDGES: Seattle’s S.R. 99 tunnel rescue resumes

Dec. 17, 2014

Following up on our story of Dec. 10, “Bertha” drill repair op is back online

On Dec. 10, Roads & Bridges reported on a halt in the operations to excavate a tunnel down to the boring machine known colloquially as “Bertha,” in order to perform repairs that would allow the machine to once more begin tunneling for the S.R. 99 project.

State engineers had voiced concerns that soil settling near the pit, apparently the result of groundwater pumped out by Seattle Tunnel Partners (STP) in the process of digging the 120-ft access pit needed to reach Bertha, was a potential hazard to adjacent buildings, as well as the viaduct itself.

The boring machine is stuck about 60 ft under a street not far from the Seattle waterfront. To remove the damaged 57-ft diameter cutting head, the 80-ft diameter access pit needs to be 120 ft deep. At present, it is less than 70 ft deep. Bertha has drilled only about 10% into the planned 2-mile tunnel to replace the Alaskan Way Viaduct.

It is now announced that crews will be allowed to resume excavation at the tunnel access pit, according to the Washington State Department of Transportation. Seattle Tunnel Partners expects to resume digging on the evening of Dec. 18.

WSDOT stated that it had “suspended excavation to give our team time to gather more survey data and review STP’s contingency plan for turning off the dewatering wells, should that become necessary.”

WSDOT says that data now shows recently measured settlement has stabilized. 

Sponsored Recommendations

Concrete Protection That’s Easy on the Environment and Tough to Beat

PoreShield's concrete penetration capabilities go just as deep as our American roots. PoreShield is a plant-based, eco-friendly alternative to solvent-based concrete sealers.

Proven Concrete Protection That’s Safe & Sustainable

Real-life DOT field tests and university researchers have found that PoreShieldTM lasts for 10+ years and extends the life of concrete.

Revolutionizing Concrete Protection - A Sustainable Solution for Lasting Durability

The concrete at the Indiana State Fairgrounds & Event Center is subject to several potential sources of damage including livestock biowaste, food/beverage waste, and freeze/thaw...

The Future of Concrete Preservation

PoreShield is a cost-effective, nontoxic alternative to traditional concrete sealers. It works differently, absorbing deep into the concrete pores to block damage from salt ions...