EARTHQUAKE / THE LONG ROAD BACK : MTA Closes Downtown Subway to Examine Strength of Tunnels

The Downtown Los Angeles subway, although it sustained no visible earthquake damage, will be shut down this weekend to allow technicians evaluating the tunnels’ structural integrity to complete their work, officials said Thursday.

The testing is not related to any safety hazard, but the closure of the tracks will help a special investigative panel to complete its work within the next few weeks, according to Metropolitan Transportation Authority officials.

The Red Line was closed Monday because of quake-related electrical problems and reopened Tuesday.

The announcement of the weekend closure came as transit officials provided television camera crews and reporters a tour Thursday of a tunnel under construction near MacArthur Park.

The durability and structural soundness of the 1.8 miles of twin tunnels now in service between Union Station and Pershing Square are subjects of an ongoing inquiry by a panel of three specialists appointed by the MTA. The panel is also examining the remaining tunnels on the Red Line.

Evaluation of the structures has been under way since fall, after a Times report that tunnel segments were built with concrete thinner than the 12 inches specified by designers. The panel, whose work has been described as wholly independent of the MTA staff, is expected to issue its findings sometime next month.

On Thursday, however, MTA rail construction President Edward McSpedon told reporters that instrumentation data gathered by the tunnel panel showed that Monday’s quake caused no changes in any of the pre-existing cracks.

“Since the (instrumentation) equipment was down there, we did ask whether there was any noticeable change in those cracks. And the answer was, ‘No, the cracks have not changed, related to the earthquake,’ ” McSpedon said.

Later, MTA officials said that only visual inspections, and not measurements, had been performed.

Two other MTA officials, along with Federal Transportation Administration head Gordon J. Linton, said that the tunnels, by surviving in apparently good condition, have passed an important test.

“The riding public can be assured of the safety of the Metro Red Line,” said Chairman Richard Alatorre, a Los Angeles City Council member.

However, Alatorre and Chief Executive Officer Franklin E. White also said that final judgments about the tunnel should be withheld until the special panel issues its report.

Michael Gonzalez, an aide to White, said that in addition to evaluating the concrete thickness, the testing this weekend will seek to verify the proper placement of rods of reinforcing steel. Called rebar, the rods are crucial to helping the tunnels withstand the bending forces of an earthquake, according to engineers.

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Caltech professor emeritus George W. Housner, an authority on earthquake design engineering, said the MTA’s panel, having already identified the cracks that existed in the structures before the quake, should check for any changes. Noting that seismic measurements of ground-shaking intensity in the Central City showed up to two times less impact than nearer the San Fernando Valley epicenter, Housner said Downtown structures still received motion that was moderate to strong.

Housner chaired a state government commission that studied the disastrous 1989 Loma Prieta quake and made recommendations regarding the design of structures and transit systems.

Edward J. Cording, a soils engineering specialist who is the chairman of the MTA’s tunnel panel, declined to discuss the group’s work before its findings are made public.

However, Richard P. Kennedy, an engineer employed by the tunnel panel as a seismic expert, said in an interview before the earthquake that the cracks in the tunnels between Union Station and Pershing Square are out of the ordinary.

“There are cracks in the concrete that are bigger than desirable,” Kennedy said. “Clearly, the tunnel isn’t built in accordance with the design in certain locations. It’s too thin; there may not be the rebar.”