AP/Wideworld Caltrans will have a cost estimate of damage and repair needs by end of the month.

California’s Dept. of Transportation is still investigating the cause and extent of damage at the site of an Oct. 12 multi-vehicle pileup on Interstate 5 near Santa Clarita in Southern California. The accident caused a concrete-popping fire in the southbound truck-only bypass tunnel.

The Friday-night fiery freeway pileup involved 30 tractor-trailer trucks. It killed at least three people and completely closed a section of the main traffic lanes near Santa Clarita until Monday morning. The truck tunnel remains closed.

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The cause of the crash, which occurred at 10:20 p.m. in the southbound I-5 truck tunnel, is still unknown, says Kwan Lam, a Caltrans division office chief for structure, maintenance and investigations. He says it will take between one and two more weeks before Caltrans determines the total cost and extent of damage.

The two-lane tunnel is a 550-ft-long reinforced concrete boxed girder built in 1975 and normally handles about 19,306 trucks per day. It was last inspected in April, and no problems were found, Lam says. However, funding has been authorized for emergency repairs, should they be needed.

The Caltrans-designed structure, known as the Newhall Pass Tunnel, runs under the main eight-lane freeway overhead, which is supported by the tunnel’s concrete roof. It is located just north of the intersection with the 14 Freeway.

Lam says preliminary Caltrans assessments so far show that the fire damaged both sides of the tunnel, causing concrete spalls as large as 6 ft by 10 ft along a third of the tunnel’s length.

“Reinforcements are exposed in these spalls,” says Lam. “Near the northern end of the tunnel, the concrete pavements have many concrete spalls, approximately 2 in. to 3 in. deep and about 1.5 ft by 2 ft in size.”

Caltrans officials say that concrete split apart after temperatures reached 1,000 F to 1,400 F inside the tunnel during the fire, which raged all day Saturday and included numerous explosions. The inferno reduced wrecked vehicles to chunks of molten metal and killed two men and a six-year-old boy. The California Highway Patrol says that 10 people also were injured in the chain-reaction crash.

Caltrans Director Will Kempton stated at the scene on Saturday that he does not think the structure will have to be replaced. Caltrans regional director Douglas Failing added Sunday that there appears to be no major damage to the freeway deck and that concrete girders supporting the structure appear intact. He said it would most likely be months before Caltrans reopens the southbound lanes.

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Steel shoring (right) has been added to the tunnel as Caltrans officials examine concrete spalling with core samples (left) that resulted from fiery crash involving 30 trucks on Oct. 12 (top).

For added safety, Caltrans has placed support beams in the tunnel to reinforce the concrete girders. As crews complete their investigation, Lam says Caltrans will begin the process of advertising and awarding an emergency-repair contract.

The 1,381-mile-long I-5 is California&rsquos main commercial highway, stretching from the Mexican border to Canada. Caltrans estimates about 230,000 motorists use this stretch daily.