At least nine people were killed on Sunday (Dec. 2) morning in Japan when hundreds of tons of concrete fell from the ceiling of the Sasago Tunnel west of Tokyo.
Aging ceiling bolts—which may never have been replaced since the tunnel opened in 1977—and an incomplete inspection in September may have caused the tunnel ceiling to give way about 8 a.m. Sunday, said Ryoichi Yoshikawa, head of maintenance at Central Nippon Expressway Company (NEXCO), the tunnel's operator.
Between 180 and 330 concrete slabs, each weighing approximately 1.2 tons, smashed down on commuters, news reports said.
"Superannuated (bolts) may be" the cause of the tunnel collapse, Yoshikawa said. "There is no record that shows repair work was carried out in the past."
|Wikispaces / CCTV|
News reports said that anywhere from 180 to 330 concrete slabs dropped onto cars in the tunnel.
The company said a routine inspection in September showed no irregularities, but it admitted that hammer tests had not been conducted on the section of ceiling that later collapsed.
The Sasago Tunnel is located about 50 miles west of Tokyo in Yamanshi Prefecture.
Inadequate Inspection, Old Bolts
According to expressway officials, failed bolts were found at the site where the concrete panels crashed down, trapping 30 cars, filling the tunnel with smoke, and ultimately killing at least nine people.
Inside the tunnel, concrete slabs sit on metal plates, which are bolted to the ceiling, and the bolts are reinforced with adhesives.
"At this moment, we're presuming that the top anchor bolts have come loose," said Motohiro Takamisawa, chief of NEXCO's Otsuki safety center, according to CNN. He added that the bolts hadn't been changed since the tunnel first opened; however, a company spokesman said that was not the company's official statement.
Officials said that the tunnel was inspected in September, but that the inspection involved only flashlights and binoculars to check the sections attached to the tunnel ceiling, according to The Asahi Shimbun.
"There was no record that we conducted the tapping inspection at the top of the ceiling in the tunnel," said a NEXCO spokesman.
Inspections were ordered for 48 other tunnels with the same design as the doomed Sasago Tunnel.
The company's 2011 annual reported that "although hammer tapping test is commonly carried out to investigate concrete structures, it takes enormous time and cost to conduct the test on all concrete structures we have."
Yoshikawa reportedly admitted that the hammer tests should have been carried out.
"That is something we need to reflect on. I offer a profound apology," he said. "We will deal with the victims in a sincere manner."
The Japan Daily Press called the statement "one of the most inadequate apologies since the Fukushima crisis."
There are 48 other tunnels with a similar design to the Sasago Tunnel, with ceiling sections suspended by metal rods anchored by bolts. The Transport Ministry has ordered expressway operators and regional bureaus to check the safety of those tunnels.
The Central Nippon Expressway Company is one of the three main operators of expressways and toll roads in Japan that were established when the Japan Highway Public Corporation was privatized.