Collapse of Yamaguchi University is being blamed on failure of `` anchor bolts '' The bolts secure concrete slabs to the ceiling of the tunnel . NEXCO says it 's unsure how long the process could take . Forty-nine people died when concrete slabs fell on traffic on the late 1970s around 8 a.m. . Forty-nine other tunnels of similar construction are being inspected across Takamizawa .
Collapse of Yamaguchi University is being blamed on failure of `` anchor bolts '' The bolts secure concrete slabs to the ceiling of the tunnel . Forty-nine people died when concrete slabs fell on traffic on the late 1970s around 8 a.m. . Forty-nine other tunnels of similar construction are being inspected across Takamizawa .