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Wednesday, Dec. 5, 2012
Disaster raises safety concerns
The Sunday collapse of a portion of the ceiling of the Sasago Tunnel on the Chuo Expressway in Yamanashi Prefecture, crushing three vehicles and killing at least nine people, has raised serious and widespread concern about the safety of road tunnels throughout Japan. This accident clearly was caused by human neglect.
Inside the 4.7 km-long tunnel, some 180 concrete panels forming a length of the tunnel ceiling fell, covering a distance of some 130 meters. Each panel is 5 meters long, 1.2 meters wide, 8 cm thick and weighs 1.2 tons. At the very least, expressway companies and the central and local governments must carry out thorough inspections of the reported 48 other tunnels that share the same design as the Sasago Tunnel to prevent similar accidents.
The Sasago Tunnel, which was opened for use in 1977, features an older ventilation system called transverse ventilation that utilizes ceiling panels to circulate air by bisecting the upper half of the tunnel. Two rows of ceiling panels are attached to either side of the tunnel wall and to 5.3-meter-long metal rods that are fastened to the tunnel roof by bolts at 1.2-meter intervals. The bolts are not threaded into the tunnel roof but rather attached by metal glue. It is suspected that the bolts anchoring the metal rods failed, causing the ceiling panels to collapse. Some bolts were found to have fallen from the tunnel roof.
In September, workers went inside the space between the panels and the tunnel roof for a routine inspection that is carried out every five years, and checked the rods and bolts. However, Central Nippon Expressway Co. (CNEC), operator of the Chuo Expressway, admits that the workers carried out visual inspections but did not conduct hammering tests to find irregularities. CNEC admits that records do not show major repair work having been carried out in the past or any bolts having been replaced. Clearly the maintenance and inspection by the company was perfunctory. If it had carried out thorough inspections in September, it likely could have detected the irregularities and made the necessary repairs.
Of the 48 other tunnels that share the same structure as the Sasago Tunnel, 39 of them are on expressways and nine others on national highways. Every possible means including hammer tapping and ultrasonic methods as well as infrared ray examinations should be mobilized to examine the safety of these tunnels.
The Sasago Tunnel accident has highlighted Japan's aging infrastructure that was built during the high economic growth period. For example, some 360 tunnels maintained by Japan's six expressway companies are more than 30 years old. These companies and the central and local governments must ensure that these tunnels are properly maintained. Strict maintenance procedures should be introduced for both new and old structures to ensure that another accident like the Sasago Tunnel collapse will not occur.