AASHTO Journal, 24 July 2015
The contractor for Seattle’s Alaskan Way Viaduct Replacement Program now expects to open the SR 99 tunnel for traffic in the spring of 2018, the Washington State Department of Transportation announced.
That would be nearly three years past the original schedule, news agencies reported, in a major project that stalled when a giant tunnel boring machine became stuck while tunneling in December 2013.
It took many months for Seattle Tunnel Partners to excavate a vertical shaft so it could bring up the boring head to be repaired. Crews brought the machine up in March, repairs are now under way and the contractor projects that machine – called “Bertha” – will resume digging out the tunnel in late November.
WSDOT said July 17 the contractor had begun installing a new main bearing on the tunneling machine. “Machine repairs are scheduled to wrap up this fall,” the announcement said. “STP and manufacturer Hitachi Zosen will then perform an extended series of tests to ensure the machine is ready to complete the tunnel drive.”
After Bertha gets back to tunneling, it is expected to emerge at the north end of downtown Seattle about a year later, although WSDOT said “the state is not able to verify the contractor’s schedule.”
In addition to beginning the main bearing installation, WSDOT said the contractor’s crews installed parts of a new seal system that will protect the bearing. Other modifications, the agency said, include addition of reinforcing steel, new monitoring systems and upgrades to prevent clogging.
“Fully disassembling and assessing the machine was always the key to determining how long the repairs would take,” said Chris Dixon, STP project manager. “We want to reassemble the machine and resume tunneling as quickly as possible, but we also want to ensure the repairs are done right.”
The cause of the damage to Bertha has not been determined. “Responsibility for costs associated with the delay will be determined through the process outlined in the tunnel contract,” WSDOT said.