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As you can see I emphrasised the "mostly" which I think is strange to word it that way. If it was mostly the steel pipe, then perhaps there must be something else as well.
A buried steel pipe is mostly to blame for stopping the giant tunnel-boring machine Bertha, which has been stuck since Dec. 6 along the Seattle waterfront near South Main Street.
Here is the image of the head of the most boring machine in the world. You have to wonder what made it stop...
Picture is from popsci article rickymouse linked and that works in east Canada.
The contingency fund is 20% apparently but they have had that labour dispute which stopped tunnelling for some weeks too.
Bertha is unable to chew through steel. A railcar or metal beam would need to be plucked out. It’s unknown whether the blockage will lead to cost overruns. Tunnel builders might conceivably file a claim based on “differing site conditions” that state studies didn’t predict. The Highway 99 contract includes contingency funds for such cases.
Currently the tunnel is behind schedule. They are considering options like increased work hours to get the project back on schedule. Right now they can still get it back on time, but at some point in the near future that won't keep them on time. The only reason it is still on budget is because STP and the other contractors are still working out the price tag and who is paying for the last two issues.
The 17.5m diameter machine currently stands about 60ft (18m) - still with only just one TBM diameter of cover - below the junction of South Jackson and South Main streets, to the west seafront side of the viaduct (Fig 1). On Wednesday of last week (18 December), crews were able to turn the machine's screw conveyor and remove some material from the excavation chamber to allow a quick view through one of the man locks at the top of the machine, states the WSDOT release. It continued that "nothing extraordinary" was observed in the chamber before it began to fill quickly with water and the lock door had to be closed.
* On Dec. 7, our contractor, Seattle Tunnel Partners (STP), began prepping the machine and surrounding environment so crews could inspect the cutterhead and excavation chamber safely.
* On Dec. 17, a brief visual inspection of a small section of the excavation chamber and cutterhead found dirt, sand and cobbles – nothing unusual.
* Over the holidays, STP crews were on-site to drill dewatering wells, maintain the machine and switch out cutting tools on the machine’s face.
* Earlier this week, STP drilled 17 small-diameter, exploratory holes near the front of the machine to see if they could identify an obstruction. They encountered obstructions in four of the holes.
* On Jan. 2, the water pressure was low enough and enough soil was removed from the excavation chamber to inspect the top 15 feet of the chamber.
* This inspection showed an 8-inch-diameter steel pipe protruding through one of the many openings in the cutterhead. We believe the steel pipe is a well casing installed by WSDOT in 2002 after the 2001 Nisqually earthquake to better understand how groundwater flows through this area. The location of this pipe was included in reference materials in the contract.
* We also believe at least some of the obstructions found by the exploratory holes are pieces of the 2002 steel pipe, which could be a contributing factor in the delay of boring.
* Other potential factors include changing soil conditions that may have caused excessive wear of cutting tools, potential objects in front of the cutterhead or objects in the lower portion of the excavation chamber that still aren’t visible.
STP is considering several options to remove the steel pipe and identify other potential obstructions.
Washington's transportation secretary is again defending the Seattle tunnel project, despite telling lawmakers in a letter Wednesday there have been a number of concerns since the tunneling machine launched in July.
WSDOT Secretary Lynn Peterson told lawmakers she has asked for answers to questions about the project including why the world's largest tunneling machine was operated at "extremely high temperatures" before it was shut down in December after running into an obstruction, and what the contractor is doing to make sure it can deliver on the project as promised.
But Peterson refused to criticize the contract or the contractor during an interview Thursday with KIRO Radio's Dori Monson, insisting WSDOT is just keeping oversight.
"If we weren't strong owners, we wouldn't be doing what we've been doing since the actual construction of the machine itself, which is ask the hard questions," Peterson said. "We just want to make sure that before Bertha goes any further below Seattle that we have all the answers we need to feel confident that she can make the entire run."
“All of our ground investigation out in front of the machine has been inconclusive,” he said.
Trepanier said the pipe might not be the only problem. “I think maybe that is a contributing factor," he said. "But there are other issues that are being dealt with and wanting to be understood at this point in time on why this machine stopped.”
There have been difficulties, he said, with material not flowing correctly through the machine and wear to its metal teeth, which weigh about 1,200 pounds each.
“I don’t necessarily agree with the word stuck,” Trepanier said later, referring to Bertha’s current status. “The cutter head turns, you can mine with this machine. It would be like driving in your car and the warning light is coming on and telling you to stop.”
Teams of five to six people will clean and examine the cutter in three-hour shifts, working in air at 1.4 times atmospheric pressure, the paper said. Then, the crew members will spend one hour in a hyperbaric tank aboard the tunnel drill to gradually decompress to normal pressure.
In order to prepare the examination area, workers had to pump out groundwater away from the surrounding soil. A ‘slurry’ of bentonite clay was sprayed in, to stick to the soil walls, allowing a water and air-resistant crust to form. The procedure allows compressed air to be pumped in a 5 foot chamber, pushing outward to prevent water and soil leaks, the Times reported.
The state DOT has said that a buried steel pipe is only partly to blame for blocking Bertha, but managers would not describe their other theories when asked earlier this week.
Interesting wonder if the block has something to do with the old streets/Seattle underground.