It could take at least two to three years to repair a sewer rupture found after a road collapsed in Yashio, Saitama Prefecture, according to the head of a prefectural panel studying the repairs.
The panel chief, Hiroaki Morita, said that such a period would be necessary if the entire sewer needs to be replaced, citing the possibility that the sewer is severely corroded inside.
The road collapse, which occurred late last month, created a sinkhole into which a truck fell. Search efforts are underway for the 74-year-old driver.
As possible causes of the road collapse, Morita cited corrosion in the sewer caused by sulfuric acid from sewage-derived hydrogen sulfide, and a gap in the sewer's joints caused by the weight of vehicles on the road or an earthquake.
Hydrogen sulfide could easily be generated in the sewer as its uneven internal structure causes sewage to be churned, said Morita, a professor at Nihon University who specializes in sewer engineering.
The sewer has been in use since 1983. An inspection by the prefectural government in fiscal 2021 found that it did not need immediate repair.
Noting that it usually takes a long time for a sewer to develop a hole, Morita said he does not believe that a huge hole appeared in the years after the inspection.
"When we consider how to repair it, we need to find out why it was broken," he said.
With your current subscription plan you can comment on stories. However, before writing your first comment, please create a display name in the Profile section of your subscriber account page.