A ceiling inspection of the Tokyo-outbound section of the Chuo Expressway's Sasago Tunnel found 670 defects and other problems, the government and highway operator said Thursday, based on checks carried out after concrete ceiling panels in the inbound tunnel section collapsed earlier this month, killing nine people and injuring two.
Of the total, 632 problems were linked to anchor bolts used to secure the steel structure attaching the concrete ceiling slabs to the tunnel roof, said the Ministry of Land, Infrastructure, Transport and Tourism, and Central Nippon Expressway Co.
Two bolts had fallen off, 608 were loose and 22 had partially come off due to corrosion. There were 38 defects found in bolts used in other parts of the steel structure.
Central Nippon Expressway said around 12,000 anchor bolts are installed in the 4.7-km outbound tunnel. In addition, there are about 51,000 other bolts on metal parts bridging the ceiling slabs and the tunnel roof above them. The ceiling level leaves a gap above it to the roof to accommodate ventilation conduits.
On Dec. 2, ceiling panels in the Tokyo-bound tunnel collapsed over a section stretching around 130 meters. Three vehicles were crushed.
The Chuo Expressway, which links Tokyo with Komaki, Aichi Prefecture, was opened to traffic gradually between 1967 and 1982. The Sasago Tunnel was opened to traffic in 1977. The tunnel ceiling never underwent major repairs, and earlier reports indicated the bolts securing the ceiling to the roof were never given thorough checks because they are not visible for inspection.
The transport ministry said it has completed emergency checks on 57 of 59 tunnels with structures similar to the Sasago Tunnel and has found problems and defects in 14 of them, but added there are no immediate safety troubles.