Crossing the Line : Platform Buckling at Station

Water-saturated fill beneath the Del Amo station has caused part of the Metro Blue Line to sink more than an inch since April, buckling the trolley line’s elevated concrete platform and forcing trains to slow to a crawl as they enter.

Yellow flags and flashing lights greet trolleys as they approach the station and the Rapid Transit District has instructed its operators to pull up to the platform gingerly. The government agency responsible for building the station says it is safe.

“There is no danger whatsoever,” said Laurence Weldon, the Blue Line project manager at the Los Angeles County Transportation Commission. He said private consultants hired by the commission, which supervised construction of the Blue Line before turning it over to the RTD, blame the problem on “differential settlement” of dirt.

Weldon said repairs should run several hundred thousand dollars, but the exact cost will not be known until the project is bidded. Whatever the cost, he said the commission will try to recover it from the private contractor they say is responsible for causing the problem.

The station rests atop a large, open concrete box filled with dirt. When heavy rains hit in March, runoff from the platform filtered through the rock ballast on which the tracks rest and percolated into the fill dirt.

Normally, Weldon said, the water would drain out of the box through “weep holes” at the bottom. Weldon said that the contractor who landscaped the station covered the holes with topsoil and plants, blocking drainage.

“When the ground gets wet, it gets inordinately heavy and it starts exerting extraordinary pressure on parts of the fill, which has settled unevenly,” Weldon said. Water saturation was so bad that the box on which the station is built “became like a . . . swimming pool, to be perfectly frank.”

Markings penciled on the side of the buckled platform indicate that the problem was first measured April 2, when the northern part of the platform had sunk one inch. It has sunk another quarter of an inch since then.

The short step now bisecting the 20-foot-wide platform is temporarily masked with 20 inches of steel plate held in place with gaffer’s tape. Thinner sheet-metal flashing is secured with screws to the platform’s sides.

The subsidence is barely noticeable to riders as they enter and leave trains.

Weldon said the commission already is looking for contractors who can jack up the station and inject additional fill under the platform to prop it up. This, along with the clearing of the weep holes, will fix the problem, he said.

Weldon said the commission is negotiating with the company that built the station, Morrison-Knudson Co. Inc. of Boise, Ida., and the company that installed the landscaping, Marina Contractors of Irvine, to try to recover the cost of repairs.

Company officials were unavailable for comment Friday.

The Blue Line cost $877 million to build, $192 million more than stated when ground was broken in October, 1985.

Weldon said there is no evidence the subsidence indicates a larger, more fundamental problem with station design or construction. The box on which the station is built was filled with appropriate material applied in three-foot layers, properly compacted.

Weldon added that the commission’s outside contracting advisers, Transportation Consultants of California Inc., have reviewed the records and found them in order.