Stalled for more than a year Bertha, the Highway 99 tunneling machine, has began churning again — toward the daylight of a deep repair pit.
By Lewis Kamb, February 18, 2015
After more than a year, Bertha — the Highway 99 tunneling machine
stalled beneath downtown Seattle — began her slow chew through 20 feet
of concrete late Tuesday on her way toward the daylight of a deep repair
And by Wednesday afternoon, the damaged boring device had moved more
than 6 feet in all, state Transportation Secretary Lynn Peterson told
Project contractors Seattle Tunnel Partners (STP) “managed to move
Bertha forward today,” Peterson told the Senate Transportation
Committee. “ ... She’s now 6 feet through.”
STP started operating Bertha at 10:15 p.m. Tuesday as part of a
rescue plan that requires the machine to mine through the concrete on
its way to the 120-foot-deep access pit. Once inside, crews are expected
to lift the broken part of the machine to the surface for repairs.
By 7 a.m. Wednesday, Bertha had managed to mine more than 3 feet,
prompting the Washington State Department of Transportation (WSDOT) to
issue a news release on the machine’s progress. By 4 p.m., when Peterson
briefed the Senate committee, Bertha had moved another 3 feet.
“The machine is at an angle, so the first part of the move went
through dirt on the lower end of the machine,” WSDOT spokeswoman Laura
Newborn said in an email Wednesday afternoon. “The majority of the
mining, however, has been in concrete.”
After the 2-yard trudge, contractors halted Bertha’s forward progress
for the day to begin building a concrete support ring inside the tunnel
— the 151st ring to be installed.
“Mining will resume after the ring has been built,” a WSDOT news release said.
Transportation officials have declined to say how long they think
Bertha’s slow journey to the repair pit might take or how long it will
take to fix the machine.
But because Bertha is damaged and prone to overheating, the trek is
expected to go slowly. Bertha might also have to take periodic breaks
along the way, should the machine become too hot, officials have said.
Contractors were keeping a close eye on Bertha’s heat levels Wednesday, Peterson told lawmakers.
“Her temperature — everybody’s worried about her temperature,”
Peterson said. “They are keeping it at a very slow, even pace as they go
through this to make sure she does not overheat and to ensure there is
no further damage to the machine.”
Bertha’s re-start is the latest screw-turn in the saga of the
troubled Alaskan Way Viaduct replacement project, started in 2012.
STP’s $1.35 billion undertaking aims to dig and construct a nearly 2-mile-long highway tunnel from Sodo to South Lake Union.
The tunnel contract is part of an overall $3.1 billion project to
replace the aging, earthquake-damaged viaduct, a key segment of the
north-south highway corridor through Seattle.
When digging began, Bertha’s tunneling work was expected to be
finished by last October, with the new tunnel scheduled to open to
traffic by the end of 2015.
But so far, Bertha has only mined about 1,000 feet.
Custom-built for the project, the world’s largest-diameter tunneling
machine first overheated on Dec. 6, 2013. The machine was shut down
about 60 feet underground near Pioneer Square. STP later determined
Bertha had a damaged rubber-seal system and main bearing. Since then,
Bertha has moved only a few feet.
To repair the machine, STP dug and constructed the access vault to
perform the needed fixes. Crews completed chipping a circle into the
pit’s south wall Tuesday to allow Bertha an easier breakthrough when it
eventually moves into the pit.
Once inside, repair crews plan to disassemble parts of Bertha before a
giant crane hoists her 4 million-pound front end to the surface,
Newborn said. The crews then plan to make alterations to Bertha’s
cutterhead, and replace the bearing and damaged rubber seals.
Still to be determined is who will pick up the tab. Last year, STP
requested $125 million for the repair work, but the WSDOT denied that
request, claiming it had “no contractual merit.”
Since then, STP has asked that the state pay an additional $22.3
million for costs tied to excavating Bertha’s repair pit. As of last
Friday, the department said it was reviewing those change-order
As the project runs behind schedule, the WSDOT also disclosed last
week that a section of the viaduct between South Main Street and
Railroad Avenue South sank another quarter-inch in the past month.
Damaged in the 2001 Nisqually earthquake, the viaduct has gradually
settled since then, sinking by as much as 6 inches at Yesler Way.
Transportation officials have said the viaduct remains vulnerable to future earthquakes but remains safe for everyday use.
During her briefing to lawmakers Wednesday, Peterson noted, “The viaduct is being monitored, and there has been zero movement.”