MTA Tunneling Resumes After 2nd Long Delay

A subway tunnel digging machine ground to a prolonged halt in the Santa Monica Mountains for the second time in six months, waylaid for nine days when it hit an unexpected fault zone 600 feet underground, the MTA acknowledged Thursday.

The giant machine, which was trapped for six weeks in July and August in a similar stretch of highly fissured sandstone, stopped Nov. 12 because falling rock made plowing forward too dangerous, said Charles Stark, Metropolitan Transportation Authority project manager. Miners had to shore up the tunnel with extra sets of steel support ribs and fiber-enhanced concrete before work resumed this week.

Tunneling contractor Traylor Bros./Frontier-Kemper was stymied in several attempts to advance in the next few days as rock continued to fall into the tunnel despite repeated attempts to solidify it with injections of cement grout, Stark said. The rotating blade at the front of the 300-foot-long boring machine was pulling the loose rock into the tunnel instead of grinding through it, he said.

“That is not an acceptable occurrence,” he said. “We don’t want to make a bigger hole than we need.”

On Monday, he said, the contractor called in a specialist to harden the rock around the tunnel by injecting foam-like grout that expands like a sponge to fill voids in the sandstone. The contractor managed to restart mining late Wednesday, and had advanced 12 feet by Thursday afternoon, Stark said.

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Metro Rail officials repeatedly denied in interviews with The Times last week that the machine, nicknamed Thelma by miners, had been halted again in the mountains. Stark said Thursday that the machine was not squeezed tight by expanding rock as it was during the summer, but nevertheless could not advance safely.

The explanation did not impress Rocky Rushing, a deputy to state Sen. Tom Hayden (R-Los Angeles), who has helped Hollywood Hills homeowners obtain information from the MTA about the tunneling.

“Whatever words they use, they spell out delays, increased costs and not being honest with the public,” Rushing said.

The troublesome tunnel is the easternmost of twin passages that by 2000 are expected to carry commuters 2.2 miles through the mountains from Studio City to Hollywood. Miners have advanced 3,116 feet since May, a rate of about 35 feet a day.

In a related development, the MTA sent a letter to Traylor Bros. on Monday stating that a five-month investigation had led the agency to conclude that the contractor was to blame for the summertime construction accident. The letter accuses the contractor of using steel support ribs that were not strong enough, installing steel plates at the bottom of the ribs that failed to bear weight properly, and designing its digging machine in such as way that the diameter of the tunnel was too small.

In prior letters obtained by The Times, the contractor has accused the MTA’s engineers of failing to accurately represent the type of rock it would face in the mountains. A geotechnical expert hired by Traylor Bros. said contract documents instructed the contractor to expect a soft rock; instead, he said, the material was more like soil.

The cost of materials used to shore up the tunnel over the summer has been estimated by the agency at a minimum of $2.5 million. The cost of delays has been estimated at about $1.7 million.