A subway tunneling machine trapped by squeezing earth under the Santa Monica Mountains will have to be partially disassembled, and a fifth of the steel ribs supporting the tunnel behind it must be ripped out or reinforced, the Los Angeles County transit agency said Tuesday.
Disclosing its plan to fix a 210-foot section of tunnel weakened by ground that unexpectedly settled over the Fourth of July holiday, the Metropolitan Transportation Authority said its construction contractor must remove and replace 22 steel supporting arches and spray concrete over 22 more.
The MTA's new estimate of the number of 21-foot-tall steel tunnel-support segments the company must repair or replace was more than four times greater than it made last Thursday, when the MTA announced the problem in the tunnel being dug from Studio City to Hollywood.
A swelling section of soft, crushed shale had contracted the tunnel so severely while workers were away that it bent five steel ribs and trapped the subway builder's 300-foot-long boring machine, nicknamed Thelma by construction workers.
To add an extra measure of support, MTA project manager Charles Stark said the 22 four-inch steel ribs that are being torn out will be replaced with six-inch steel ribs.
After the shoring-up operation is completed, Stark said the company--Indiana-based Traylor Bros./Frontier-Kemper-- will blast away the rock trapping its machine, which weighs more than 500 tons, with powerful jets of water.
Stark said the firm expects to complete the repairs over the next week and start digging again by Aug. 2. Industry experts have estimated the cost of the repair at $1 million.
At a news conference and protest staged by state Sen. Tom Hayden at Traylor Bros.' work site in Studio City, residents of the Hollywood Hills above the tunnel route expressed new frustration about a project they have attacked for environmental reasons for two years.
"If the MTA were subject to the three-strikes law, they'd be in jail by now," said Marylane Farris, a Studio City real estate broker and hillside activist.
Homeowner Patricia Marlatt complained that the MTA had held a lavish community reception to discuss the tunneling project a week ago without mentioning the latest bedevilment.
"They don't inspire any public confidence when they have one huge, unanticipated mistake after another and don't talk to us honestly about them," she said. "Now this happens. What's next?"
Meanwhile, new questions have emerged about the MTA's official explanation of how the tunneling machine got stuck.
Stark told MTA board members last week that Traylor Bros. said it was surprised to discover after returning from the holiday that it had parked the machine in a zone of soft, crushed shale that geologists call a "shear zone." According to Stark, it was not until July 8 that the company learned that tiny fissures in the rock had opened during the long weekend and, in the parlance of miners, "relaxed" around the tunneling machine and its supports.
Essentially, the company argues, the rock suddenly grabbed the deserted Thelma in a bearhug only 940 feet into its 2.3-mile journey from Studio City to Hollywood.
But one mining industry veteran has told The Times that he believes Traylor Bros.--which is digging its first Metro Rail tunnel--ignored signs that the ground was squeezing its tunnel well before the Fourth of July.
The expert, who spoke on condition of anonymity, said he inspected the tunnel in late June and wondered why the contractor had not taken steps to shore it up.
"I could see that the ground, left alone without putting in bigger steel, would be a problem," said the miner, who has built tunnels across the country. "If it had been my tunnel, I would have put in bigger steel. It was obvious. You could see it. The only question would have been how much bigger: six-inch or eight-inch?"
In an interview Monday, Stark disputed the assertions of the miner who spoke to The Times.
"The contractor did not know, nor did we know, that we were in squeezing ground until after the July 4th holiday," he said.
The MTA's solidarity with the contractor may be strained next week, however, when the transit agency's top tunneling consultant says he will tell Traylor Bros. that it should have known it could encounter squeezing ground in that section of the mountains, and taken precautions.
The consultant, University of Alberta civil engineering professor Dan Eisenstein, said the shear zone is described in a report of the area's geology that was made available to all construction firms who bid on the tunneling contract.
"It is true that the documents don't say exactly where the shear zone would appear. But it is described," Eisenstein said.
The professor asserted that the firm should have been alert for the zone and used six-inch-wide support beams there. He also said the company should not have stopped in an area of potentially unstable ground for four days.
"When you enter a shear zone, you might not notice that the fissures are tightly closed. But if you leave a tunnel open for a period of time, the fissures open, the ground loses its strength, your support gets overloaded and then it becomes deformed," Eisenstein said. "There is a domino effect of negative factors."
Eisenstein, who downplayed the event as the equivalent of a flat tire, said he did not expect any more such shear zones, but added: "Mother Nature is unpredictable."
Traylor Bros. is prohibited under the terms of its contract from commenting to the news media.
Stark said the contractor had sent a letter to the MTA blaming the agency's subway design team--a private consulting consortium called EMC--for failing to accurately describe the type of rock its miners would encounter.