General News

Saitama Pref. Could Have Anticipated Road Collapse Risk in Yashio, Third-Party Committee Says

Provided by Saitama Prefecture
The interior of the sewer pipe almost directly under the road collapse, seen in February last year.

The Yomiuri Shimbun

17:20 JST, February 20, 2026

A third-party committee tasked with investigating the cause of a road collapse in Yashio, Saitama Prefecture, in January last year pointed out the risk could have been anticipated during a routine inspection of sewer pipes by the prefecture in February 2022 and an additional inspection should have been conducted, in a report released Thursday.

The committee established by the prefecture said in the report the prefecture had overlooked the progression of concrete corrosion during the routine inspection near the site of the road collapse.

It stated, “Had they paid more than the usual level of attention, they could have anticipated the increased risk.”

Provided by Saitama Prefecture
The interior of the sewer pipe near a manhole, seen in February 2022. Excessive splashing made it impossible to confirm the situation.

According to the report, the prefecture conducts a routine inspection once every five years. The section near the site of the collapse had such fast-flowing sewage that it could not be accessed. Thus, the inspection contractor floated a camera in the sewage to record inside the pipe. Directly beneath the collapse site, excessive splashing made it impossible to confirm the situation from the footage, while the images downstream were unclear due to insufficient light.

However, the contractor assessed the pipe’s corrosion level using a three-tier scale (severe, moderate or mild) and rated it as moderate. The prefecture concluded it was “not a situation requiring immediate repair.” The third-party committee criticized this, stating the prefecture “should have attempted an additional inspection.”

The sewer pipe at the site is enormous, with a diameter of 4.75 meters, and constantly carries a large volume of sewage. The committee concluded that “repair from inside the pipe is difficult.”

Regarding the cause of the collapse, the analysis remained unchanged: hydrogen sulfide from the sewage corroded the sewer pipe, creating small gaps. That allowed soil to get into the pipe, forming a cavity underground, which caused the collapse.