Hitachi Zosen was surprised when WSDOT, which is a party to the suit against the insurance companies, started behaving as if it didn’t want the insurance money. WSDOT asked the court to move the case to Thurston County, where WSDOT and STP were battling each other in a separate lawsuit over who should pay for the additional costs resulting from the damage to Bertha. If the two had been combined, the insurance case, the simpler of the two lawsuits, might have been delayed and lost in the complexity of the multiple parties and multiple claims arising from the project. The logic? Success against the insurers would imply external issues like the steel casing might have played a role in the damage to Bertha, thereby putting the state in a weaker position vis-à-vis STP.

WSDOT declines to comment directly on its legal strategy, issuing this statement: “WSDOT has always denied Seattle Tunnel Partners’ claims that an eight-inch steel well casing caused the tunneling machine damage.”

Hitachi Zosen, long averse to litigation, reluctantly joined the fray. It countersued STP for the $25 million it says it was never paid for the boring machine, and an additional $80 million for repairs to Bertha.

Hitachi Zosen executives say their primary interest is in finding out what really happened so it can manufacture even better machines. Based on evidence gathered so far, Soichi Takaura, general manager of the company’s Shield TBM unit, believes the damage was caused by a combination of improper operation by STP and the machine’s encounter with the well casing.

Bertha was an earth pressure balance machine (EPBM) designed to work with many varieties of soil and sand. It’s a device Hitachi Zosen has special expertise in building. For the machine to work, even pressure must be maintained on the face of the tunnel as the cutter head scrapes away rock and soil. Various additives are mixed into the soil to make it a toothpaste-like substance that can be drawn into a chamber behind the cutter head to apply balancing pressure against the tunnel face. That pressure is controlled by a massive corkscrew that draws soil from the chamber and out on a conveyor belt to its back end, where the soil can be transferred to trucks and carried away. When that mixture gets too soft or too hard and cannot be drawn through the chamber, the machine can have trouble moving forward and can overheat.

In late August, Hitachi Zosen executives, from left, Yukinobu Nakamoto, Shinji Ogaki and Hidetoshi Hirata posed

in South Lake Union at the northern end of the viaduct replacement tunnel dug by Bertha.

Because the machine had a diameter of nearly 58 feet, substantially larger than any previous tunneling machine, operators were simultaneously dealing with many kinds of soil, says Shinji Ogaki, Hitachi Zosen’s project manager at the Seattle site. He points to a chart displaying the clay, gravel and other soils Bertha had to contend with, which may have made operating the machine more complicated than those the operators had been accustomed to.

Howard Handewith, a Seattle-based tunneling expert, suspects the industry may be reaching the limit to how big boring machines can get. “I admire good Japanese engineering,” he says, “but nobody had built a machine that big before, so nobody could have known what it would do.”

The unprecedented size of the cutter head also may have made the machine more difficult to manipulate. Among the many innovations Hitachi Zosen incorporated into Bertha at the request of STP and WSDOT were special atmospheric chambers that would allow workers to adapt more easily to the high-pressure environment required to do maintenance, such as replacing worn cutters. That capability was designed to allow STP to complete the project more quickly, but it also required the cutter head to be substantially thicker, making it harder to maneuver.

Whatever the reason, Ogaki says, some of the operators driving the machine had trouble keeping the soil at the right consistency. There were times when the soil was as hard as concrete, requiring workers to use jackhammers to loosen it so it could be carried through the conveyor system. Although Ogaki says he suggested to STP in several instances that it use more additives to soften the soil, the contractor declined to do so. He says he is not sure whether the high cost of the additives was a factor in that decision.

“When you face conditions like that, you should slow down and get the soil mixture right,” says Takaura. If STP kept pushing when the soil was hard and the machine kept reaching high temperatures, that could have stressed the machine and made it more susceptible to damage when the machine hit the casing, he says. “The pipe may be just 8 inches in diameter, but when it gets inside the machine, it will do damage.”

“Even if a sports car is advertised as being able to go 200 kilometers an hour,” Takaura adds, “that doesn’t mean you can take it out on some dirt mountain road and go that fast. These machines have to be treated properly.”

One possible factor, says Hitachi Zosen, could have been STP’s desire to complete the project quickly. Under the contract, the company would have earned an additional $25 million if the tunnel could be completed 10 months ahead of what was already an aggressive schedule, giving STP a strong incentive to push the machine to its limits. STP declined to comment on its operation of Bertha, but reiterated that it was the steel well casing that damaged the machine.

Hitachi Zosen believes that when Bertha hit the well casing, the steel got tangled up in the teeth of the machine’s cutter head, damaging the teeth and making it harder for the machine to continue digging. Pieces of the pipe also broke off and were sucked into the machine, clogging its innards. When the machine wouldn’t progress, and even after it flashed warning signals, the operators continued to push Bertha forward. The 27,000 kilowatts of power driving the machine, instead of being applied to carve the soil, turned into heat, damaging the seals and allowing debris to enter and impair the machine.

Governor Inslee’s statement that Bertha should have been able to cut through the well casing “like cheese” reveals a fundamental misunderstanding of how tunnel-boring machines work, says Hirata. “Boring machines don’t cut,” he says. “They scratch at the surface of the soil or rock and then scrape it away.”

Most tunneling experts agree the machines are not designed to deal with metal, one reason the concrete wall Bertha ground through to start its journey was reinforced with fiberglass bars rather than steel. But many experts are also skeptical that the casing alone could have damaged a machine of Bertha’s size.