Modifying Machines May Enable Subway Excavation to Resume : Transit: MTA officials say North Hollywood work may begin in a month if hoods on equipment are extended forward to stabilize soil ahead of the digging.

Modifying two high-tech tunneling machines to help prevent loose earth from sinking should enable subway excavation beneath Lankershim Boulevard to resume in about a month, transit officials said Thursday.

After just two months of fitful work, digging beneath North Hollywood stopped at the beginning of April when workers detected a half-inch of subsidence at the tunnel face. The $65.4-million project has been stalled since, as the Metropolitan Transportation Authority and its contractor hash out how best to deal with the sandy soil that makes tunneling in the area difficult.

MTA spokesman Steve Chesser said the agency’s experts have recommended extending the hoods of the tunneling machines a few feet forward to stabilize the soil ahead of the actual excavation.

The adjustments will take place in two phases, because only one of the tunneling machines is actually in use at the moment, Chesser said. Workers will first modify the machine that has yet to begin tunneling, then retrofit the other.

To reach the second machine, which has already excavated about 200 feet of the twin tunnels, workers will dig a 50- to 60-foot shaft down from the surface of Lankershim just north of Magnolia Boulevard--an operation that the agency acknowledges could negatively impact businesses in the area. Other merchants near the construction site have complained of noise and dust.

“We’re going to do everything we can to minimize that,” Chesser said.

Workers will probably begin the modifications next week and complete the changes in about three to four weeks. Tunneling--already behind by two months--would resume thereafter.

Chesser said it has not been determined how much the modifications to the tunneling machines--which are worth hundreds of thousands of dollars--will cost. He said the MTA expects the contractor, Obayashi Corp. of South San Francisco, to foot the bill because the company “didn’t have it right in the first place.”

Although Chesser said Obayashi has agreed to the MTA’s plan to extend the hoods on the machines, the company had disagreed with the agency on the best course of action and who should pay for it. Obayashi had argued that injecting grout into the soil prior to tunneling--a potentially expensive remedy for the MTA--was the best solution.

Representatives from Obayashi declined to comment Thursday.

The unfriendly soil conditions in North Hollywood are similar to those in Hollywood, where tunneling caused the surface to sink nearly a foot last summer. Two months ago in North Hollywood, the ground sagged five inches at the tunnel face, but the settlement was barely perceptible at street level.