Tunneling Machine Is Stuck Under Mountains

Metro Rail subway tunneling has ground to a halt beneath the Santa Monica Mountains because a giant digging machine became wedged in rock while workers took four days off for the long Fourth of July weekend, according to county officials and documents.

Sedimentary rock under the Cahuenga Pass relaxed and squeezed the 300-foot-long machine, bending five segments of tunnel liner behind it, according to a Metropolitan Transportation Authority construction executive.

Work crews have been digging around the clock to pull the broken segments out and free the machine, but said they did not expect success until the beginning of August.

“We only tried to move it Tuesday. It didn’t move,” project manager Charles Stark said.

The MTA called in an expert who told board members Thursday that they “should not push the panic button” because there is no danger of a tunnel collapse.

“Two things went wrong at the same time,” University of Alberta professor of civil engineering Dan Eisenstein said in an interview after an inspection. “The builder stopped for four days in exactly the wrong place. If they had just barreled through without halting, the situation would have been much less adverse.”

The entrapped tunnel-boring machine, nicknamed Thelma by construction workers, is now just 960 feet along its 2.3-mile journey beneath the mountains from Studio City to Hollywood. Its job is to create a passage for the Red Line subway. Thelma is stuck 220 feet below Fredonia Drive in the northernmost of two tunnels that are expected to carry commuters downtown by 2000.

A twin digging machine, nicknamed Louise, has been delayed in its mission to excavate a tunnel for trains headed in the opposite direction while engineers modify its cutter head to match conditions encountered by Thelma.

Thelma is as long as a football field and looks like a giant, mechanical centipede operated by a crew of a dozen workers. In front, its rotating head grinds like a Cuisinart’s cutting blade against the rock. Inside, a 200-foot system of conveyor belts crushes the rock and sends it into four train cars that regularly return to the start of the tunnel. The dirt is lifted out of an 80-foot shaft by a crane and tossed into trucks for a trip to a dump.

Officials refused to estimate what the new problem would cost the tunneling contractor or the MTA after costs of repair, re-engineering and delays are totaled.

An expert familiar with Metro Rail tunneling, who declined to be identified, estimated that the price tag for re-mining to be close to $40,000 a day--or about $900,000 if the job takes the expected 3 1/2 weeks.

Despite Eisenstein’s assessment that the contractor could have avoided the problem by forgoing a long holiday weekend, Stark declined to point a finger at the tunneling contractor, Traylor Bros./Frontier-Kemper.

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 the digging machine would encounter.

Defending the designers, Eisenstein said the fold of crushed shale that appears to have locked the digging machine in a squeeze would be “impossible” to detect in advance. EMC had noted “the possibility” that such a fault might lie across the tunnel’s path, Eisenstein said.

A 230-foot tunnel section supported by four-inch steel ribs bent under the weight of the rock behind the digging machine’s cutter blade, Stark said.

EMC’s contract specifications called for the tunnel to be supported by four-inch steel ribs at four-foot intervals in some places, and six-inch steel ribs at four-foot intervals where the rock was softer, according to Stark.

As a precaution, Stark said, the contractor is replacing the four-inch steel ribs with six-inch steel ribs at two-foot rather than four-foot intervals. A heavy steel mesh is placed between the ribs to prevent the rock from falling.

Traylor Bros. won the job in 1994 with a low bid of $124.4 million, but three other bidders estimated that the job would cost $142.1 million to $148.9 million, according to MTA records.

An executive for one of the losing contractors, who declined to be identified, said his firm believed that the tunnel should be supported by precast concrete segments--as are all other tunnels in the Metro Rail system--rather than the steel ribs.

“There’s no comparison in the strength,” said the executive, who has built other Metro Rail tunnels. “It’s like using a matchstick vs. a 2x4. The bottom line is that someone was trying to save money by not putting in the right material.”

Stark disputed that observation. “Our best information is that the rock conditions here do not call for concrete segments.” He said he was unaware that any bidder had proposed to use concrete segments.

Although the MTA was expecting to carve through hard rock in that stretch of tunnel, the first 2,710 feet proved to be a soft rock called Topanga shale.

The tunneling machine, designed to move forward by pushing hydraulic arms against hard rock, was bogging down even before it got squeezed, according to progress reports filed with the MTA.

Eisenstein offered to take a Times reporter into the tunnel to examine the situation, but the MTA refused to allow the joint visit.