Machine Stuck Since July 4 Is Freed

With evident relief, a county transit official announced Thursday that a giant subway tunnel digging machine that had become stuck deep in a tricky section of Santa Monica Mountains shale since July 4 has finally been freed.

Metropolitan Transportation Authority construction chief Stanley Phernambucq told the agency’s board members at a committee meeting that the agency’s tunneling contractor had made two major modifications to the machine’s digging mechanism to help it gnaw a bigger hole through the rock.

The extra four inches of diameter, he said, will help prevent the 300-foot-long machine from becoming lodged again in zones of heavily faulted rock that geologists call “squeezing ground.” The machine began to burrow south again at 10:20 a.m, he said.

However, two MTA board members angrily demanded a report detailing the events that led up to the immobilization of the machine over the Fourth of July weekend.

The Times reported Sunday that daily tunnel inspection reports filed by MTA’s construction management consultants described cave-ins and difficulty in installing steel tunnel support ribs three weeks before the holiday. The reports, according to experts contacted by The Times, should have provided ample evidence that the ground was squeezing, making the tunnel smaller, well before the machine became stuck.

Board member Nick Patsaouras tersely told the construction chief that he had been promised a chronology of events by Monday afternoon, and then again by Thursday morning. “I still haven’t seen it yet. . . . You seem to take this so lightly,” he snapped.

Patsaouras also questioned whether the MTA’s engineering consultants had drilled enough deep test borings in the Santa Monica Mountains to determine exactly the type of rock that its tunneling contractor would encounter.

Project manager Charles Stark said geotechnical experts had not yet concluded whether the contractor--Indiana-based Traylor Bros./Frontier-Kemper--or the MTA was at fault for the long, embarrassing delay in tunneling in the Cahuenga Pass.

He said that it was the contractor’s responsibility to decide the appropriate way to support its tunnel. The MTA’s contract, he said, specified that the builder could either use six-inch-wide steel ribs to hold up the tunnel, or a heavy grade of steel mesh stapled into place with long metal dowels called expansion bolts.

Before Traylor Bros. began work, he said, its executives received permission to use four-inch-wide steel ribs in certain places rather than the six-inch ribs or expansion bolts, where it believed the ground would be firmest.

The first 730 feet of the tunnel were supported by rings of six-inch-wide steel ribs; the next 210 feet were supported by rings of four-inch-wide steel.

Asked to explain why he believed the ground came in on the tunneling machine, Stark said: “The only mistake, if one was made, was that we did not switch back to six-inch ribs soon enough.”

To shore up the tunnel, the MTA ordered Traylor Bros. to replace 44 sets of four-inch steel ribs with six-inch ribs. Only eight sets of four-inch steel supports will remain in the tunnel, Stark said.

Patsaouras, an electrical engineer as well as a longtime regional transit specialist, castigated the construction executives for writing the contract in a way that gave such a range of choices to the builder.

“That’s not engineering. To say you can do either this or that is baloney,” he said.

Alistair Biggart, who heads the engineering consortium that is managing the construction project for the MTA, said it is the practice of governments worldwide to let tunneling contractors choose their support from a range of choices. He noted that the Santa Monica Mountains tunnel starts with 2,630 feet of soft Topanga shale and ends two miles later in diorite, “one of the hardest rocks known to man.”

Biggart, a veteran of the English Channel tunnel project, said the contractor was doing “extremely well indeed” in a twin tunnel being excavated alongside the one where the digging machine became stuck.