At least 60 percent of the anchor bolts used in Yamanashi Prefecture’s Sasago Tunnel weren’t as strong as they were designed to be, the infrastructure ministry has learned after surveying the site of a fatal ceiling collapse.
Nine people were crushed by concrete roof slabs in the tunnel last December when anchor bolts used to affix the ventilation separation wall to the roof apparently failed, allowing the wall to drop. Since the wall, which ran down the midline of the tunnel, was holding up the ceiling panels, they collapsed onto the road, crushing the vehicles.
The bolts are supposed to bear three to four times the average estimated load of 1.2 tons each. But the ministry found that 113 of the 183 bolts tested failed when subjected to three times the average load, and 16 of them couldn’t even withstand 1.2 tons of pull.
The ministry reportedly believes the problem may have been caused by a lack of adhesive to affix the bolts to the roof, degradation of the adhesive, or rusting.