Bolts: Guilty Again

When there is a mechanical disaster, so many times it is a failed bolt at fault. This time, too, the collapse of the roof of the Chuo Expressway's Sasago Tunnel is blamed on aging bolts.

Here is the report from The Japan Times online edition:

Tuesday, Dec. 4, 2012


Fatal tunnel collapse blamed on aging bolts

Kyodo


KOFU, Yamanashi Pref. — Sunday's expressway tunnel collapse in Yamanashi Prefecture that killed at least nine people may have been caused by aging ceiling bolts that failed, Central Nippon Expressway Co. said Monday.

Facing reporters Monday in Nagoya, where the highway operator is headquartered, Ryoichi Yoshikawa, CNEC executive in charge of maintenance, said failed bolts were found at the site where tons of concrete ceiling panels fell onto vehicles traveling through the Sasago Tunnel.

"Superannuated (bolts) may be" the cause of the tunnel collapse, Yoshikawa said, suggesting the bolts were never replaced. "There is no record that shows repair work was carried out in the past."

The two rows of fallen panels were attached to either wall and suspended from the tunnel's roof by metal rods running down its center. CNEC revealed that the tunnel hadn't undergone any major repairs since it opened in 1977. The company stressed that a routine inspection in September showed no irregularities, but admitted they did not conduct hammer tests on the ceiling section that collapsed Sunday.

Yoshikawa also admitted that hammer tests, used to detect, by sound, irregularities in assembly components not visible or physically reachable, should have been carried out.

"That is something we need to reflect on. I offer a profound apology. We will deal with the victims in a sincere manner," he said.

According to the transport ministry, there are 48 other tunnels similar in design to the Sasago Tunnel, in which the ceiling sections hang under the roof, suspended by metal rods anchored by bolts. The rods are embedded in a vertical panel that extends down from the center of the roof to meet the ceiling panels and runs through the tunnel, providing ventilation shafts on either side of the panel over the roadway.

The ministry has ordered five expressway operators and its regional bureaus to check the safety of those tunnels.

In the accident, about 180 concrete ceiling slabs — each measuring 5 meters by 1.2 meters and 8 cm thick — collapsed along a 110-meter section of the road about 1.7 km from the Tokyo end of the tunnel, the police and highway operator said. Each slab weighs 1.2 tons.

The company began conducting emergency checks Monday on the Enasan Tunnel in Nagano and Gifu Prefectures, and the Tsuburano and Fujikawa tunnels in Kanagawa.

The Sugo Tunnel in Tokyo, the Kyotanabe Tunnel in Kyoto, the Nagao Higashi and Nagaodai tunnels in Osaka, the Shiwa, Takedayama and Aki tunnels in Hiroshima, and the Kanmon Tunnel in Yamaguchi and Fukuoka are also expected to undergo checks.

Police early Monday had confirmed that nine people died in three vehicles trapped inside the 4.7-km Sasago Tunnel.

In a vehicle that was believed carrying six people, police and firefighters found the bodies of three men and two women, all in their 20s and from Tokyo. A 28-year-old female banker from Kanagawa Prefecture who was in the vehicle survived.

They also confirmed the deaths of a man in his 70s, a woman in her 60s and another in her 70s, all in the same vehicle, as well as the death of a trucker, identified as Tatsuya Nakagawa, 50.

The Sasago Tunnel was opened to traffic in 1977.

Discussions on repairing the nation's aging tunnels, most built during the high economic-growth era of the 1970s, have moved at a snail's pace.