Reports reveal frantic effort to keep Bertha tunneling
Newly released reports contain information that could help Hitachi-Zosen, the manufacturer, troubleshoot how the giant tunnel machine broke down. The chronology almost certainly will factor into any disputes between Seattle Tunnel Partners and the state over who pays for cost increases.
Seattle Times transportation reporter
Seattle Tunnel Partners spent three work shifts trying in vain — as temperatures spiked, motors shut down and mud flooded in — to budge its giant boring machine after stalls Dec. 6 and 7, newly released records show.
Daily reports by state inspectors explain how the contractors discussed probing the soil from above to look for an obstruction.
But before doing so, they pushed the $80 million drill near its limits, in hopes of breaking through a mysterious clog in the watery soil.
“Unable to move machine forward efficiently all shift. Thrust force and torque are running very high,” says a Washington State Department of Transportation (WSDOT) wrap-up from the day shift Dec. 6.
Two of the 24 huge electric motors that turn the round cutterhead automatically tripped off, and were reset.
“High temperatures in the main drive are causing shutdowns of machine as well,” the inspector wrote. Two more attempts during the swing shift also failed.
Before and after the drilling attempts, workers wanted to open a hatch to peer at the cutterhead, but the area was filling too quickly with groundwater. The drill advanced only 4 feet that entire day, after moving as much as 32 feet per day earlier in the week.
WSDOT on Tuesday released Highway 99 tunnel quality-verification reports for Dec. 2, 3, and 6 to The Seattle Times, after a public-disclosure request. The state previously released reports for other days of the week, including Dec. 7, when the machine known as Bertha overheated again, sand was found in grease around the bearings, and operators decided to stop drilling.
The quality reports contain information that could help Hitachi-Zosen, the Osaka, Japan-based manufacturer, troubleshoot how the machine broke down.
The chronology almost certainly will factor into any disputes between Seattle Tunnel Partners (STP) and the state over who pays for cost increases to the $1.44 billion contract. The state already is questioning some of STP’s decisions.
Of course, the machine is now stranded, after digging 1,025 feet of the 9,270-foot route from Sodo to South Lake Union. Rubberized seals that protect the main bearing, and possibly the bearing itself, need to be replaced. Drilling will restart Sept. 1 or later.
State officials sent the contractors 11 questions about how they’ve operated the machine. Transportation Secretary Lynn Peterson told state lawmakers in January she’d had “concerns” since drilling began in July.
“What are the factors and decisions that led to operating the TBM (tunnel-boring machine) at extremely high temperatures before the shutdown on the afternoon of December 6. Were any fail safe mechanisms overridden during the period leading up to shut down?” one question says.
Chris Dixon, STP’s project director, vigorously defended the work in a reply letter Jan. 15, released by the state.
He says the contractors followed a preset threshold of 60 degrees Celsius (140 degrees Fahrenheit), then adjusted it to try mining at 65 C, and quit before the machine breached its true limit of 70 C.
“The final fail safe temperature was never changed or exceeded,” he wrote.
He also charted how the excavation rate plummeted soon after Bertha hit a buried steel pipe, left over from state groundwater tests in 2002 and 2010.
The quality reports don’t mention the buried steel pipe — an indication workers on the front line didn’t immediately see a crisis when Bertha struck it Dec. 3.
An email the next morning, from a supervisor with tunneling company Dragados USA, said a search of state records couldn’t find any abandoned wells. The worker surmised the pipe was so shallow it didn’t tangle with the cutter at all:
“The tunnel crown is approximately 48’ (deep) at this location and judging by the straight verticality of the pipe, it would make sense that the bottom of the pipe (well screen) was above the crown and TBM pressures pushed it straight up.”
Steel fragments were found later that day in the conveyor system.
Dixon theorized at a news conference Feb. 11 the pipe gouged some cutting teeth and wrapped around the face, which kept it from scraping away dirt. Instead, the soil squeezed through without crumbling and became stuck in the cutterhead gaps, he said. Dixon’s letter to Peterson was headed “Re: PCO #0250 — TBM Obstruction,” a warning of a potential change order to bill the state for the December stall.
The state’s Dec. 2 quality report raises a previously unknown issue: Scales that weigh the excavated soil in the front and the back end of the conveyor were uncalibrated and gave different readings. That’s not necessarily a big deal along the waterfront, where the Alaskan Way Viaduct is shielded by a row of buried pilings — the “tunnel in a box” strategy, to isolate the machine during its early shakedown phase.
But if the scales aren’t adjusted, the results could be dire later — tunnelers need to keep an accurate record of how much soil they remove, or risk causing voids or settlement that damage the viaduct or downtown buildings.
“That’s one of the things that need to be proofed out during this test section,” said Matt Preedy, deputy program administrator for WSDOT.
Voids happened in recent years above both King County’s Brightwater sewer tunnel and Sound Transit’s Beacon Hill light-rail tunnel. In response, WSDOT required multiple muck-measuring systems, and 900 sensing devices on streets and buildings.
Based on January inspections of the cutter face, the December stall was caused by soil clogging the cutterhead, Preedy said.
But he said the exact reason for the clog remains under investigation by STP.
Under the design-build contracting method, the state is supposed to keep arms length from the builders, so that private companies are responsible for their tools and decisions.
WSDOT runs a risk that if it micromanages the job by telling STP how to run the machine, the state might wind up absorbing liability later.
Think of the Highway 520 bridge — the state took the design of the pontoons in-house, and therefore will spend $208 million for repairs and delays due to cracking in the first batch from 2012.
Preedy reiterated the public should have patience, and the contractors need time to reach correct conclusions about how to finish the job.
“I’m confident they are 100 percent dedicated to this task, and at the end of the day they will pass muster,” he said.
Mike Lindblom: 206-515-5631 or email@example.com. On Twitter @mikelindblom