1,100 cave-ins, cavities on Japan's highways in 10 years; over 40% triggered by pipe damage
TOKYO – More than 1,100 cases of cave-ins and underground cavities were confirmed on national highways across the country between fiscal years 2015 and 2024 , according to a recent analysis by The Yomiuri Shimbun.
Of this number, more than 40 per cent were caused by surrounding soil and sand flowing into damaged underground pipes, as with the cave-in that occurred earlier in 2025 in Yashio, Saitama Prefecture, according to the analysis.
It was also found that about 20 per cent of the incidents were caused by construction defects, such as insufficient ground compaction. Furthermore, nearly half of the cases occurred within a one-kilometre radius of a similar incident. An expert has stressed the need for the government to strengthen the maintenance and management of national highways.
In the Jan 28 incident in Yashio, part of the surface of a prefectural road suddenly collapsed at an intersection, and a truck traveling along the road fell into a sinkhole. It is believed to have been caused by damage to a pipe installed in 1983, which allowed surrounding soil and sand to flow into it, creating an underground void.
The sinkhole subsequently expanded to 40m wide and 15m deep. The truck driver died in the incident, and sewer use was temporarily restricted in 12 municipalities within the prefecture.
To conduct its analysis, The Yomiuri Shimbun requested the disclosure of relevant information from eight regional development bureaus and the Hokkaido Regional Development Bureau under the Land, Infrastructure, Transport and Tourism Ministry, as well as the Cabinet Office's Okinawa General Bureau. Overall, these bodies manage 24,000km of national highways.
The Yomiuri then collected documents reporting cave-ins and cavities that were detected in the 10 years from fiscal year 2015 to analyse factors including the dates and times, locations, scale, causes and repair methods. Incidents for which reports were not compiled were also included in the analysis if they had been made public.
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At least 1,157 incidents – 730 cave-ins and 427 cavities – had been reported. The prefectures with the highest number were Kochi with 78 cases; Ishikawa 63; Tottori 62; Chiba 59 and Shimane 55.
A total of 509 cases, or 44 per cent, were caused by surrounding soil and sand flowing into corroded or damaged pipes, or deteriorated joints, creating cavities underground.
Construction defects totaled 259 cases, or 22 per cent, with most of these resulting from insufficient compaction of the ground during road construction or pipe laying.
In addition, 276 cases, or 24%, were attributed to such factors as decayed tree roots, the collapse of nearby slopes, earthquakes and typhoons.
There were 521 cases in which a cave-in or cavity occurred within a one-kilometer radius of another such incident on the same highway, more than 40 per cent of the total.
At the Omano intersection on National Highway Route 4 in Koshigaya, Saitama Prefecture, three cave-ins occurred between 2022 and 2024 due to corrosion and damage to the same drainage pipe.
'At present, the government hasn't yet been able to fully grasp the precise picture of road sinkholes and cavities,' a senior ministry official said in response to the analysis results.
'We will expedite efforts to investigate and proceed with establishing a system to quickly grasp the underground situation.'
'Many national highways are designated as emergency transportation routes in the event of a disaster. If the risk of sinkholes is left unaddressed, road cave-ins could be a frequent occurrence during an earthquake, delaying rescue and relief efforts,' said Professor Reiko Kuwano, a professor of geotechnical engineering at the University of Tokyo.
'The government needs to work with entities in charge of underground infrastructure to strengthen the maintenance and management system for national highways,' Prof Kuwano said. THE JAPAN NEWS/ASIA NEWS NETWORK
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PHOTO: PASARFISH 'They just bought it from this fish trader from Jurong Fishery Port from a random bucket.' The fish's identity was unravelled on the same day with the help of Major-General William Farquhar, the first British resident and commandant of colonial Singapore. A Google search of the fish's features netted a 19th-century picture from the Farquhar Collection, a series of watercolour paintings by Chinese artists of flora and fauna that the leader commissioned. Said Mr Ong: 'It was a perfect match.' The painting was labelled in a neat, slanted script, with one of its local names, ikan biang biang, otherwise known as the shorthead hairfin anchovy. The pair theorised that the fish was likely commonly found at markets back then. The mystery of the anchovy stemmed from the fact that it had been forgotten and people now no longer know how to cook it, they concluded. The coastal fish is common in Indonesia and Malaysia, where it is usually fried or salted. 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'The fact that it is uncommon in the trade in Singapore could lead to its inclusion into social history and trends of consumption.' Such resources can aid comparative studies as well as the tracking, tracing and managing of fish reserves. Wet markets can also be treasure troves for discovering new fish. Dr Tan said: 'Not all fish are possible to catch with your own hands or set of tools. I would rely on fisherfolk for their skill set with larger nets to fish from deeper waters.' Through forays into local markets in Indonesia, his team has uncovered new species such as the Crossocheilus obscurus carp and Hemibagrus velox catfish. Yellowtail fish, which are traditionally overharvested, being sorted into baskets at Jurong Fishery Port on June 20. ST PHOTO: ANG QING On a grim note, considering a fish weird can be a symptom of overconsumption. Worldwide, overharvesting has driven marine species' populations down, erasing them from collective memory as they become harder to find. This was witnessed during Pasarfish's market tours to raise awareness about seafood heritage and sustainable consumption, said Mr Lek, when only older folk recognise the species sold. I joined Pasarfish on one such tour at 2am on June 20 to learn more about Jurong Fishery Port, Singapore's sole port for fish. The cacophony of different tongues reflects the international diversity of the port's wholesale market, where about 100 merchants display piles of fresh seafood kept fresh with ice. There was hardly a moment of stillness throughout the two-hour tour. Sweaty men in yellow rubber boots processed prawns, sorted fish and shouted at idle buyers to get out of the way as they dragged baskets of slimy produce. Mr Ong and Mr Lek's knowledge was apparent, as out of more than 80 species of seafood at the port that they shared details about, only one species baffled them. After a brief search online, they identified it on their Instagram page as the Hawaiian ladyfish. Three ocellated parrotfish at Jurong Fishery Port. One of these was given away for free during the June 20 Pasarfish tour, a common practice for unpopular fish. ST PHOTO: ANG QING Another unusual fish we saw is the ocellated parrotfish that a fishmonger gave to Mr Ong for free, a practice often used to dispose of unpopular catch and build rapport. Eating certain fish perceived to be strange, however, can be a good choice, as doing so can be more sustainable for popular species. During the tour, our group of six encountered varying sizes of yellowtail fish, traditionally used to make fish balls. Mr Ong explained: 'This was historically one of the most common fish in Singapore. But they're not as common any more because the fish stocks are depleted.' He pointed out that the smaller yellowtail we spotted were signs of overfishing and unsustainable practices, with the fish not having had time to grow before they were caught. Instead, Mr Ong recommended using a wider range of fish for fish balls to avoid pressuring a single species. Other substitutes that can and have been used include wolf herring, milk fish and pike conger. To help consumers make better choices, Pasarfish plans to launch a guide of 60 common fish from its year-long survey by listing their local names, price ranges and sustainability recommendations.
