TOKYO - Across Japan, aging underground infrastructure is leading to a rising number of road collapses, with an estimated 10,000 cases annually—about 29 per day. Nearly 30% of these incidents in urban areas are attributed to deteriorating sewer pipes.
With such risks looming in everyday life, what measures can be taken to prevent another tragedy like the one in Saitama? Investigating the current state of underground infrastructure, experts highlight the challenges standing in the way of effective solutions.
The accident occurred two weeks ago. "I heard a loud bang, and when I looked, the road had caved in," a local resident recalled. The incident took place at an intersection in Yashio City, which borders Tokyo’s Adachi Ward. A truck fell into the hole as the ground collapsed beneath it. The driver, a 74-year-old man, initially responded to emergency calls, but as the hole widened and a utility pole fell, the situation became increasingly dangerous. His truck's cabin was buried under debris inside a deformed sewer pipe. While rescue efforts continued, his whereabouts remain unknown.
Similar incidents have occurred nationwide. In 2016, a massive sinkhole near JR Hakata Station in Fukuoka rapidly expanded, swallowing traffic lights and growing into a 30-meter-wide, 15-meter-deep crater. Last September, another large-scale collapse struck a residential area in Hiroshima City, submerging streets and prompting evacuation orders for nearby residents. The impact of such incidents extends far beyond the initial collapse—four months after the Hiroshima accident, displaced families were still unable to return home.
What causes these sinkholes? According to Reiko Kua, a civil engineering professor at the University of Tokyo, "In many cases, a large sewer pipe located deep underground deteriorates and breaks. The damage allows surrounding soil to be washed away, forming an underground void that eventually causes the surface to collapse." Kua's team conducted experiments simulating the process, demonstrating how even a small leak in a sewer pipe can lead to a major sinkhole. Because these voids form deep underground, there are often no visible warning signs until a collapse occurs.
To prevent sinkholes, some municipalities have begun using advanced detection methods. In Nara Prefecture, for example, authorities recently conducted emergency inspections using trucks equipped with ground-penetrating radar to scan for underground voids. However, Kua notes that even these methods may not always detect deep-seated cavities like those that caused the Saitama accident. "If the sewer pipe is shallow, surface distortions may appear before a collapse. But in cases where the pipe is deeper, voids can grow unnoticed, making early detection difficult," she explained.
According to the Ministry of Land, Infrastructure, Transport, and Tourism, Japan experiences an average of 10,000 road collapses per year, with sewer pipes accounting for 10% of cases nationwide and nearly 30% in urban areas. The fundamental solution lies in replacing aging sewer systems, but this process faces major hurdles.
One of the biggest challenges is budget constraints. Katsuyuki Kawai, a professor at Kinki University, points out that cities like Osaka have roughly 5,000 kilometers of sewer pipes, with half needing replacement. "That means about 2,500 kilometers require urgent repairs, but at the current pace, only 50 kilometers are being replaced annually due to limited funding," Kawai said. Since sewer infrastructure is largely invisible to the public, maintenance tends to be deprioritized until a major incident occurs.
Adding to the problem, a labor shortage across the construction and maintenance sectors is further delaying necessary repairs. While technologies like the SPR (Spiral Pipe Renewal) method—where a new pipe is built inside an old one without excavation—have helped reduce costs and disruptions, progress remains slow.
"Infrastructure maintenance often takes a backseat to new development projects," an industry expert noted. "But as this tragedy in Saitama shows, neglecting maintenance can have severe consequences." Without sufficient investment in repairs, aging infrastructure could turn from a vital lifeline into a dangerous liability.
The risk of sinkholes is not limited to Saitama—similar threats exist across Japan. Yet, a fundamental solution remains elusive, and time is running out as underground infrastructure continues to age.
Source: YOMIURI
