Hitachi-Zosen has decided to add 86 tons of steel ribs and plates to stranded tunnel-boring machine Bertha, in hopes of making it more stout when drilling resumes next year.
Highway 99 contractor Seattle Tunnel Partners announced today that its repair plan includes 216 steel pieces. Some will reinforce the bearing block, which surrounds the rotating drive system, and some will strengthen the front body, next to the spinning cutter face.
STP has posted an animation of the repair project. The most spectacular feature will be a crane lift of the entire 2,000-ton front end, which will be set on the surface, disassembled, and repaired next to Elliott Bay.
The added weight suggests that Hitachi-Zosen engineers, who designed the $80 million machine, have noticed vibrations or some other structural problem during the first 1,021 feet of drilling last year, or maybe in a 4-foot test drill in January. But when asked about that today, Chris Dixon, STP project director, says he hasn’t been briefed yet about what happened to make reinforcement necessary. The world-record, 57-foot, 4-inch diameter machine, working in wet and abrasive Seattle soils, is testing the limits of tunnel boring machine (TBM) technology, which has evolved toward greater girth for more than a century.
The plates “will enhance the overall rigidity of the TBM and improve its performance,” Dixon said.
He said STP remains on track to restart drilling in March 2015, which he called an aggressive schedule. However, he said there’s also a month of “float,” or time cushion, if Bertha can be reassembled and begin testing by January.
This month, workers from Malcolm Drilling have installed 23 of 73 deep, vertical shafts to form a repair pit. Bertha will drill forward to enter the repair pit, where a crane by Mammoet will make the lift.
A new bearing will be installed, after sand and groundwater penetrated seven bearing seals last year. Dixon said it’s unknown yet whether the old bearing was damaged.
STP, which is working under a $1.44 billion contract, has said repairs and delays could cost more than $125 million. The contractor has asked the state to pay, but WSDOT has denied the request. Dixon and Todd Trepanier, WSDOT’s Highway 99 administrator, were reluctant to talk about the dispute Monday, a possible sign their priority is to pull together and get the job done.
Meanwhile, about 250 workers are onsite, mostly to build the north and south portals, Dixon said. STP is trying to gain time on non-drilling features of the project — for instance, by installing electrical lines and utility rooms along the western edge of the tunnel tube this year, instead of waiting until after Bertha’s done drilling.
When tunnel boring began July 30, the WSDOT was advertising a December 2015 date for the four-lane tube to open for traffic between Sodo and South Lake Union. Now the team is aiming for fall 2016.