Arch Replacement Delays Tunneling Again

A Metro Rail subway builder will delay the resumption of tunneling through the Santa Monica Mountains for at least another week because it must replace 22 more support arches weakened by settling ground, the county’s transit agency said Thursday.

The postponement is the third since the contractor’s digging machine became trapped in the mountains over the Fourth of July holiday. The new estimate brings to 44 the number of 4-inch tunnel arches that must be ripped out and replaced by stronger, 6-inch arches. That is double the previous reckoning and almost nine times the number the builder said would have to be replaced just two weeks ago.

The slowdown and additional repair cost will add to a bill that was already over budget well before the tunnel-boring machine, nicknamed “Thelma” by workers, got snagged in siltstone 940 feet into its 2.3-mile journey from Studio City to Hollywood.

According to figures released this week in a monthly report by the federal government, which foots half the bill for the subway construction, the cross-mountain tunnel was 51 days late and at least $4.3 million over budget by June 28. The report shows that the Indiana-based contractor--Traylor Bros./Frontier-Kemper--had also asked for $6.7 million in additional payments.

Traylor Bros. won the job in 1994 with a bid of $124.4 million. If the changes pending through June 28 are approved, the cost will rise to $135.4 million.

The Metropolitan Transportation Authority has declined to estimate how much it will spend to extricate Thelma and replace the tunnel arches, but industry experts have pegged the bill for the delay alone at a minimum of $40,000 per day.

The agency has also declined to lay blame for Thelma’s entombment at the contractor’s feet quite yet.

“We’ve learned that you’re always going to find unknown situations underground, because short of drilling a pilot tunnel ahead, there’s no way to know what conditions you will encounter,” MTA project manager Charles Stark said Thursday.

Stark said the contractor last week had planned to replace just the 22 four-inch arches closest to the face of the tunnel, then shore up the next 22 segments of ring steel by spraying a thick band of concrete over them.

The agency’s engineering consultants, however, rejected that proposal, he said, asking Traylor Bros. to do more math to support its theory. Instead, Stark said, the contractor decided to replace all the thin rings with the thicker ones.

Once the new steel is in place, Stark said, miners will reattach the tunnel boring machine’s 275 feet of trailing gear to its giant cutter head, blast free the contraption from the soft rock’s embrace with high-powered jets of water, and go forth again deep beneath Cahuenga Pass.

Meanwhile, the MTA said a second digging machine two days ago embarked on a parallel tunnel. The twin tunnels are to carry commuters in opposite directions between the San Fernando Valley and downtown by August 2000.

Stark said the second machine, nicknamed “Louise,” has been modified to cut its tunnel two inches wider on each side to create enough room for bigger steel supports in the heavily faulted area that trapped Thelma, called a shear zone by geologists.

In another change of strategy, Stark said miners will install bolts through the 18-foot-wide rock pillar between the two tunnels to strengthen the excavation.