SEATTLE — The sinkhole that formed behind the tunnel machine Bertha in January followed a pattern set by a previous sinkhole on the project, and state officials expressed concern about it happening again as the machine exits a maintenance stop just before drilling beneath the Alaskan Way Viaduct.
The concerns are revealed in a January 25 letter from Brian Nielsen, the deputy program administrator for the Washington State Department of Transportation, to Chris Dixon, project manager of Seattle Tunnel Partners.
KIRO 7 obtained the letter through a public records request.
It referred to a sinkhole that formed in November 2013 as Bertha mined out of a planned maintenance stop called Safe Haven 2.
Similarly, January's sinkhole appeared as the machine mined out of a "controlled ground condition," the giant pit used to repair Bertha after a breakdown kept it from drilling for two years.
Nielsen wrote that both scenarios are similar to the planned maintenance stop, called Safe Haven 3, where Bertha is now spending about a month before tunneling beneath the viaduct.
"As you are fully aware, should tunneling out of Safe Haven 3 and under the viaduct create voids, there could be severe consequences," Nielsen wrote.
Nielsen's letter came during a halt in tunneling ordered by Gov. Jay Inslee after the sinkhole developed.
In February, Inslee lifted the tunneling suspension after six weeks.
On Wednesday, WSDOT spokeswoman Laura Newborn sent KIRO 7 a statement:
"Seattle Tunnel Partners has implemented a number of changes to ensure they can safely continue mining. Since Feb. 23, STP has safely built almost 300 feet of the SR 99 tunnel. As a precaution, WSDOT plans to close SR 99 through downtown Seattle while the machine passes underneath the Alaskan Way Viaduct."
The dates for the two-week traffic closure on the viaduct have not yet been announced.
Nielsen's January letter also said that in addition to the sinkhole, "a void of at least 12 yards has been identified, and additional voids continue to be identified."
Neilsen wrote that STP's "refusal to accept responsibility for these very serious problems" in a previous letter "illustrates a fundamental failure of leadership that puts the successful completion of this project at risk."
Letters from STP fire back at the state.
Chris Dixon wrote the suspension of tunneling was "grossly disproportionate" to the sinkhole and that the governor's decision was "wrongful" and "more fodder for WSDOT's political and media agenda."
Dixon also described the suspension as "risky," arguing keeping Bertha in place for an extended period increased the chance of future sinkholes and other problems, like muck clogging the machine.
Dixon also made clear STP planned to bill the state for costs related to the suspension "which are currently estimated to be in millions, not thousands, of dollars."
STP and WSDOT are already disputing the cause of Bertha's breakdown in 2013, which STP says is a result of the machine striking a well casing for which state officials did not provide adequate warning, a claim WSDOT vigorously denies.
STP also wrote to WSDOT saying that it intends to submit a change order requesting more money related to a barging incident in January, when excavated muck from the tunnel spilled into Puget Sound.
STP claims WSDOT directed contractors to utilize members from ILWU Local 19, which resulted in positioning unsecured barges with an assist tug, rather than positioning secured barges with deck winches, "which made it more difficult to safely and evenly load the barge in a controlled manner."
WSDOT officials responded that they never made such a demand.
Despite the war of words in January, both sides managed to work together, and the machine successfully mined without incident to Safe Haven 3.
Cox Media Group