Subway Tunnel Walls Thinner Than Designed : Red Line: Concrete flaws in some areas may add risk in a big quake, experts say. Officials say the structure is sound.

Numerous segments of tunnel in the new Los Angeles subway were built with less concrete than designed--defects that experts say might reduce the subway’s ability to withstand a major earthquake.

Metro Rail officials became aware of deficiencies late last year after their chief tunnel designer had warned in an internal memorandum that sections of tunnel built below original specifications could be jeopardized “when exposed to seismic” forces and other long-term stresses.

A consulting firm’s report later identified dozens of locations where the concrete walls of the tunnel may be only six to eight inches thick, instead of the required 12 inches. These thin areas span more than 2,000 feet of the 9,970 feet of tunnels between Union Station and Pershing Square.

But transit officials ordered the tunnel contractor to buttress only a fraction of the suspected problem areas. Thick steel plates, covering 90 feet of tunnel, were installed at three locations in time for the opening of the Red Line in January.

Officials said that more sweeping repairs did not appear necessary. They said they believe that the tunnels are safe and structurally sound.

Edward McSpedon, president of the Metropolitan Transportation Authority’s rail construction subsidiary, noted that three major earthquakes during the last two years--centered 100 to 120 miles from Downtown--had no impact on the tunnels. He said that another, less intense temblor, centered about 20 miles from Downtown, also inflicted no damage.

McSpedon said it was debatable whether installation of the three steel plates was even necessary. “It was felt, as a minimum, as a perception issue, (that) we ought to do something,” he said.

Asked whether the Union Station to Pershing Square tunnels meet the original design specifications for structural integrity, Martin Rubin, program director of Metro Rail’s design consulting team, said: “I’m not sure they meet the original design specifications . . . but we are comfortable with the structural integrity.”

The tunnels, constructed by Tutor-Saliba Corp. and a joint venture partner at a cost of $89 million--are part of the 4.4-mile Red Line, the subway component of Metro Rail. The mass transit project mainly is funded by the federal government and local sales tax revenue. Construction has been overseen by local transit agencies.

Inspection reports and other public records reviewed by The Times raise questions not only about the structural quality of some tunnel segments but also about the effectiveness of transit officials’ supervision of construction.

Officials failed to require the contractor to build the tunnels according to original design specifications. For example, reports indicate that Tutor-Saliba poured concrete for some tunnel walls even though inspectors had withheld authorization for the work.

“This is a disgrace,” said James Pott, an engineer and former member of the MTA’s Rail Construction Corp. board. “The specifications called for 12 inches. The taxpayers paid for 12 inches and they didn’t get 12 inches. If I was still on the board, I would raise hell about this.”

MTA Board Chairman Richard Alatorre said: “This is outrageous. There is absolutely no excuse” if the concrete is below the required thickness.

Newly installed MTA Chief Executive Officer Franklin E. White declined to comment Saturday, saying he wanted to familiarize himself with the issue.

The problems with the tunnel work have prompted transit officials to revamp their concrete inspection procedures, but no action has been taken against the contractor. Although Tutor-Saliba paid to install the steel plating, the company has not been billed for testing or other expenses related to the construction shortcomings.

A variety of experts contacted by The Times said the tunnel would be weaker than designed unless the contractor had added extra steel reinforcing rods, known as rebar, to compensate for the thinner concrete walls.

“If it does not have the (extra) rebar, we would be concerned with it,” said Krishniah N. Murthy, director of engineering and projects for the consulting team that designed the subway.

Charles W. Stark, the transit authority’s project manager for the subway, said that thin areas require either extra steel rods inside the concrete or the installation later of exterior steel plating.

But transit officials said they have not determined whether extra steel reinforcing was placed throughout the suspected thin sections of tunnel.

Josh Randall, Tutor-Saliba’s vice president for heavy construction, said extra reinforcing rods were installed within only about 300 linear feet of the tunnels. Randall said that in the company’s opinion, six inches of concrete is sufficient, even with no reinforcements.

Randall and company President Ronald N. Tutor attributed any thin spots to construction errors.

“These are human beings who pour these tunnels,” Tutor said. “If it came in under 12 inches, it wasn’t deliberate.”

Tutor said he was unaware that transit agency records indicated that the problem extended beyond the few areas reinforced with steel plating. He also said that he had no knowledge of his crews pouring any concrete without proper authorization.

In order to withstand the bending and compressive forces of an earthquake, the concrete subway tunnels were designed to be a minimum of one foot thick. That is the standard enforced elsewhere on the Metro Rail project, according to people involved with that work.

But public documents indicate that several stretches of the 1.9 miles of tunnels linking Union Station and Pershing Square are under the minimum. A consulting firm retained by the transit authority in August, 1992, found, through radar and ultrasound testing, that 2,082 feet of the tunnels--21% of the total--may be just six to eight inches thick. Other records indicate that the tunnels at two locations are less than five inches thick.

“Results indicate that the tunnel liner concrete is generally 10 to 12 inches thick,” concluded a report by Massachusetts-based Weston Geophysical Corp. “However, at several locations primarily along the spring line, the concrete liner is only six to eight inches thick.” The spring line of a tunnel is roughly halfway between the crown and track level.

The thin areas, the report said, have “concrete six to eight inches thick, and/or high air entrapment or air-filled void(s).” Air pockets would weaken concrete, according to experts.

Weston Geophysical said in a subsequent, October, 1992, report that the contractor “may have” installed extra rods of steel within 215 linear feet of the tunnels.

Transit officials said they did not know whether more than 215 feet of the tunnels contain the extra rods of steel.

George B. Morschauser of Parsons-Dillingham, the construction management firm that supervises all work on the subway, said the agency did not undertake further testing to search for extra steel reinforcing in part because of time considerations.

McSpedon, of the MTA subsidiary, said that in his view the average thickness of the concrete in the tunnels is adequate, because although there are thin sections, other locations are thicker than 12 inches. He also pointed out that the strength of the concrete material itself is greater than the original design specifications.

Experts said the added strength of the concrete is helpful but not a substitute for thickness.

“You just cannot say that just because you have (a strength of) x pounds-per-square-inch, you can reduce your thickness,” said Robert W. Shuldes, consulting engineer for the Portland Cement Assn., an Illinois-based group that represents concrete companies.

In the end, transit officials said they were comfortable with the structural integrity of the tunnels, based on a variety of test results.

They put more stock, they said, in test borings of the tunnel walls than in the radar testing, which Stark said “is not an exact science.” Experts contacted by The Times estimated the margin of error in radar testing at 10%.

Officials said they began taking borings of the tunnel walls in March, 1992, initially in response to water leaks. That testing, they said, showed areas with thin concrete. Later that spring, staff members were directed to perform additional tests after a former Parsons-Dillingham inspector had alleged that the concrete was defective.

On June 24, 1992, chief tunnel designer Timothy P. Smirnoff wrote in a memo that two corings brought to his attention showed that the concrete was thinner than required.

“The diminished section,” he said, “may decrease the serviceability and long-term performance of the lining, especially when exposed to seismic and other combined loadings. Further, such a variation in lining thickness must be considered a nonconformance” with the contract specifications.

“We are unaware of any investigations by contractor or construction manager (Parsons-Dillingham) to determine the limits and extent of this nonconformance nor any credit or recovery for the owner on account of this defective work,” Smirnoff concluded.

On July 31, 1992, the transit agency issued a press release saying that limited testing by a consultant had found one “small patch of thinner” concrete, near Union Station. McSpedon said “all evaluation, testing and investigation support the integrity of our construction and confirm that its safety is beyond reproach.”

Two weeks earlier, Smirnoff and his design staff noted that another coring, taken near the Civic Center station, found concrete only 4.87 inches thick. They recommended that the transit agency undertake radar testing of the entire subway and make “follow-up coring in any identified suspect areas” by Sept. 11, 1992.

Transit officials in part followed the designers’ recommendations by commissioning a more comprehensive study between Union Station and Pershing Square. They retained Weston Geophysical in August, 1992. The company used radar waves and ultrasound to measure the tunnel thickness and reported its test results to transit officials that month. Forty suspected thin areas were identified.

Records show only 19 core samples were taken from the tunnel. More than half of the samples were less than 12 inches thick, and 16% were less than 10 inches thick.

Morschauser said the list of coring locations was determined by Weston in consultation with Parsons-Dillingham. Some samples were taken, he acknowledged, from areas where thin concrete was not even suspected. Morschauser said he could not offer an immediate explanation.

These core samples and other data, officials said, were used to select the three areas of the tunnels that were repaired.

Outside engineers said in interviews that without the extra reinforcing, tunnel walls less than 12 inches thick would be more vulnerable to bending forces of an earthquake. This is particularly a concern, they said, at the spring line, or horizontal midpoint.

“In general, that would hurt its ability to withstand loads--earthquake loads or soil loads,” said concrete specialist Ziad Bayasi, an assistant professor of engineering at San Diego State University.

“It makes a huge, radical difference when the thickness goes down at the spring line,” said Michael L. Shank, a veteran Denver-based tunnel contractor whose company built two other Los Angeles subway tunnels, between Pershing Square and MacArthur Park. “When you go down to eight inches, you’d have to have twice as much steel” to try to compensate.

George W. Housner, a professor emeritus at the California Institute of Technology who played a role in early planning intended to protect the Los Angeles subway from earthquake stresses, also said that thin concrete at the spring line would be important.

“If the thickness of the wall is only 60% of its required thickness, that means that the stress would be approximately 50% greater,” he said.

How could a tunnel end up thinner than designed?

Construction experts said that such defects can result when a tunneling crew strays off course. If the bore is misaligned, it can cut into the space required for placement of a concrete tube. This, in turn, can force workers to trim the thickness of the tunnel wall.

To guard against such problems, transit officials prohibit contractors from pouring tunnels until the concrete forms are inspected.

Inspection records indicate that on at least a dozen occasions, Tutor-Saliba poured concrete into the tunnel although field inspectors had withheld authorization. On May 24, 1990, a Parsons-Dillingham inspector declined to authorize a pour in part because “forms had to be moved from proper line to allow proper thickness.”

In the area of this pour, transit officials last fall installed one of the three reinforcing plates.

The Metro Rail tunnels were the first tunnels constructed by Tutor-Saliba, a company that has built public works projects statewide and has won more than $400 million in Los Angeles subway contracts.

Tutor said his Sylmar-based company has performed high quality work and he was unaware that any concrete was poured without authorization.

“We fix things when we make a mistake,” he said.

Thin Tunnels

Concrete lining sections of two Metor Red Line subway tunnels may be 33% to 50% thinner than originally designed. The areas of suspected thin concrete cover 2,082 feet of tunnels. This raises questions about how tunnel construction was administered--and how the segments would fare during a major earthquake.

In southbound tunnel

A) Suspected problem areas: 7

Total number of feet: 1,270

B) Suspected problem areas: 8

Total number of feet: 295

In northbound tunnel

C) Suspected problem areas: 12

Total number of feet: 232

D) Suspected problem areas: 13

Total number of feet: 285

The Problem: Tunnels are supposed to contain a concrete liner that is 12 inches thick, along with rods of reinforcing steel. If the concrete falls below that level of thickness, it becomes more exposed to the stresses of earthquakes and other forces.

Where: Tunnels carrying trains in opposite directions between Union Station and Civic Center station and Pershing Square station are affected.

The Repairs: Last fall, officials ordered installation of half-inch-thick steel plates at three locations, covering 90 linear feet of tunnel, to reinforce areas of thin concrete. But officials did not reinforce dozens of other areas where thin concrete was suspected.