Expert Says Subway Tunneling Machines Increase Risk of Sinkage

The two machines now digging subway tunnels in North Hollywood are wrong for the job because they increase the risk of ground slumping, a leading expert said Thursday--even as the Metropolitan Transportation Authority is bickering with its subway contractor over blame for sinkage damage to more than a dozen buildings.

“I have said from Day 1 that I didn’t like the way the Lankershim [Boulevard] tunnels are built,” said Dan Eisenstein, a civil engineering professor at the University of Alberta.

Using a more efficient machine would have reduced by 90% the millions spent on grouting--a substance pumped into soft ground to create a firm surface through which to dig, Eisenstein told the MTA directors Thursday.

Eisenstein was appointed by Mayor Richard Riordan, an MTA board member, to lead an independent review panel of tunneling experts. He said the type of excavating machine being used in North Hollywood is rarely used anywhere in the world on sandy soil, such as prevails in the area.

The machine allows too much subsidence at the surface and demands expensive grouting to harden the ground ahead, Eisenstein--one of the world’s leading experts on tunnel excavation--said he told an MTA board meeting Thursday.

John J. Adams, the MTA’s deputy executive officer for construction, said that if the agency was “deciding on the job today,” a different type of machine would be chosen. But there was little experience three years ago with more efficient “earth balance” tunneling machines now in common use, Adams said.

Eisenstein did not directly link the tunneling for the MTA’s Red Line 60 feet beneath Lankershim Boulevard to the damage plaguing more than a dozen businesses on the street above--sinking floors, cracking walls and burst water pipes. Whether the tunneling caused the damage is still at issue.

Meanwhile, The Times obtained a copy of a letter to the MTA from the firm doing the tunnel digging, the Obayashi Corp., complaining that the MTA is trying to blame the company for damage to the surface buildings. The company in turn blamed the MTA.

In the March 27 letter, Obayashi project manager Carl Linden replied:

“After the owners of structures located along Lankershim Boulevard have complained of cracks and sinkages, the Authority has begun assigning responsibility and blame to Obayashi, when actually the onus lies within the Authority’s own organization.”

The MTA’s Adams said he could not comment on the letter.

A spokesman for Obayashi, one of the world’s 10 largest construction firms with $14 billion in annual revenues, said the company could not reply directly to questions because the MTA orders contractors not to speak to the news media.

The assessment of blame is critical because the repair bill for the damaged structures could rise to millions of dollars.

In an example of the potential for runaway costs, Los Angeles County Supervisor Zev Yaroslavsky, an MTA board member, on Thursday morning visited El Sombrero nightclub on Lankershim Boulevard--which has the worst reported damage on the street.

On Wednesday, Yaroslavsky had announced that the MTA--without conceding responsibility--was willing to pay to repair a 15-inch slump in the nightclub’s floor, estimating the bill at $20,000. On Thursday, however, he said the agency would pay as much as $100,000.

A number of El Sombrero’s neighboring businesses have joined a $2-billion lawsuit against the MTA filed by property owners in Hollywood who allege that the MTA’s tunneling also caused damage to their buildings.

Eisenstein said the ground subsidence problem in both places could have been largely avoided by using modern “earth balance” tunneling machines, which cost twice as much as the $2.5-million open-face shield model used by the MTA’s contractor.

According to engineering sources with inside knowledge of the project, the MTA’s construction management team in 1994 rejected Obayashi’s design for another kind of tunnel-boring machine that would have helped prevent ground settlement of the type on Lankershim Boulevard.

The MTA team instead favored the machine now used in the tunnel because it would cost less, move faster and allow geologists to inspect soil during the digging process, the sources said.

The MTA’s Adams would not comment on the allegations.

Grouting has caused most of the inconvenience to business owners on Lankershim Boulevard. The chemical and silicate cocktail is mixed 24 hours a day on the street with a deafening roar and injected directly into the holes in the pavement by truck-mounted machines that block curbs for a quarter of a mile at a time.

The substance also rises in a fine white cloud of powder that settles faster and wider than diligent MTA crews can clean. Business owners complain that the noise, lack of parking and dust have scared off customers.

Through March 1, the tunneling project was 367 days behind schedule because of repeatedly halting to insert grout. The latest 24-hour halt occurred Wednesday after half an inch of ground settlement was discovered outside a bank in the 4400 block of Lankershim. Before that, work had stopped March 10 for 10 days of grouting after the sinkage at the nightclub was discovered.

Interviews with business people along the two-block stretch of Lankershim found that more than three-quarters had suffered damage to floors, walls or water pipes within a month of the time Obayashi dug two tunnels that will ultimately carry northbound and southbound trains under the street.

“They are destroying my business and I feel helpless,” said Al Siegel, who has run Al’s Discount Furniture on Lankershim for 30 years.

“Last year we did $5 million here. This year we’ll be lucky to do half that. They close down Lankershim all weekend. I have six salesman on the floor looking at each other.”

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Down Lankershim

Most merchants in the 4600 and 4700 blocks of Lankershim Boulevard have reported cracks or subsidence in the floors and walls of their buildings in the wake of Metro Rail subway tunneling over the past three months.

Mid-march, Isaia & Co.: Floors buckled, walls cracked, windows popped.

Mid-January, the Pedal Shop: Floors and walls cracked.

March 19, Toyota of North Hollywood: Water pipes burst; floors and walls cracked.

Jan. 23, Winston Tire: Water pipes broke, floors and walls cracked.

March 11, El Sombrero: Water pipes broke; floors and walls cracked, Floors sank 15 inches.

March 26, In ‘n Out Stereo and Jack’s Auto Repair: Water line burst; floors cracked; roof buckled.

Mid- January, Cousins Country Cafe: Floors and walls cracked.

Mid- March, Prestige Auto Upholstery: Floors and walls cracked.

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Settling Ground

The steps leading to sinking ground:

1. Tunneling advances.

2. Soil is destabilized.

3. Topsoil settles into voids, creating trough- like depressions.

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The Shakes

Four- car muck trains weighing up to 100 tons each roll dirt away from tunneling machines every half- hour. Rails are attached directly to concrete tunnel liners rather than to vibration- diffusing wooden ties.

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Tracking the Tunnels

Obayashi Corp. miners dug the cast tunnel in January and the west tunnel in March at the fast pace of 80 to 100 feet a day.

Researched by JON MARKMAN / Los Angeles Times