Two trucks are swallowed by a massive sinkhole caused by heavy rainfall in Busan, Sept. 21. Yonhap

Seoul and other municipal administrations are increasingly deploying advanced equipment to detect and deal with sinkholes amid growing public concerns, but experts are raising doubts over the effectiveness of these efforts.

They point out the limitations of monitoring all roads within their jurisdictions and emphasize the need for local governments to focus their use of equipment, such as ground-penetrating radar (GPR), on high-risk areas, particularly where underground construction is underway.

According to a report from the Ministry of Land, Infrastructure and Transport, a total of 957 road subsidence incidents have been recorded across the country over the past five years.

The data shows 193 cases in 2019, 284 in 2020, 142 in 2021, 177 in 2022 and 161 last year, averaging 191 incidents annually.

A sinkhole incident in Busan on Sept. 21 was triggered by heavy rainfall. A massive sinkhole, measuring 10 meters in length, 5 meters in width and 8 meters in depth, swallowed two large trucks.

This caused a drainage vehicle from the Busan Fire Department, which was assisting on the road at the time, to fall into the sinkhole. A five-ton truck nearby also plunged into the hole as it passed by. Fortunately, no casualties were reported.

Since April, seven instances of road subsidence have been reported in the southeastern port city. These include one case each in April, May, and July, followed by three incidents in August, with the latest occurring recently.

Seoul is also facing a significant number of road subsidence cases. From 2021 to August this year, the city recorded a total of 63 sinkholes, making it the second-highest in metropolitan and provincial regions after Gyeonggi Province, which documented 117 incidents during the same timeframe.

Notably, an incident occurred on Aug. 29 in Yeonhui-dong, a neighborhood in Seoul's Seodaemun District, where a sinkhole measuring 6 meters wide, 4 meters long, and 2.5 meters deep swallowed a vehicle.

The accident left an 82-year-old driver with broken ribs, while his 79-year-old wife, who went into cardiac arrest, was resuscitated with CPR.

The frequency of these incidents due to subsidence of roads across the country underscores the risk of potentially severe accidents occurring at any time and in any location, raising urgent concerns about public safety.

Police and fire officials measure the depth of a sinkhole in Yeonhui-dong, Seodaemun District, Seoul, where an accident left two people seriously injured, Aug. 29. Yonhap

According to the land ministry, more than half of the sinkhole incidents have been linked to damage to sewage and water pipes.

The report from the ministry reveals that 46.6 percent of cases involved damage to sewage pipes, while 52.6 percent, or 512 incidents, were caused by issues with upper or lower water pipes.

The leaks from damaged sewage systems often pass through construction sites, leading to ground instability. Frequent vibrations and heavy loads are also key factors that weaken the ground, leading to collapses.

Other causes of road subsidence include poor refilling work, which accounted for 17.9 percent, or 171 cases. Additionally, 82 cases, or 8.6 percent, were caused by poor excavation work, as well as damage to or insolvency of other buried infrastructure.

Following a series of road subsidence accidents, the central and local governments introduced measures aimed at managing high-risk areas.

Seongdong District in eastern Seoul implemented an underground space safety management system utilizing Internet of Things technology in 2017 and has been monitoring water leaks through an underground space leak diagnosis system since 2020.

Similarly, other local governments, including Suwon in Gyeonggi Province and Cheongju in North Chungcheong Province, have adopted GPR to enhance maintenance efforts and detect potential hazards.

The Seoul Metropolitan Government also implemented various initiatives, including the use of GPR and the detection of defects in sewage pipes. However, doubts remain over the effectiveness of these efforts.

After the sinkhole opened in Yeonhui-dong in August, the city government completed restoration work by 11:15 p.m. and conducted GPR scans across all eight lanes, covering a 500-meter stretch, until 4 a.m. the next day.

Despite these efforts, another road subsidence was discovered in the morning, just 30 meters from the original site.

Both the land ministry and the city government have carried out frequent inspections of aging sewage pipes, flood-prone areas and regions with concentrated rainfall. The number of inspection points has increased tenfold compared to last year.

However, road subsidence cases in Seoul continue to rise, with cases increasing from 11 in 2021 to 20 in 2022 and 22 last year, according to the land ministry's report.

Police control a nearby lane and begin restoration efforts after a road subsidence was discovered in Yeonhui-dong in western Seoul's Seodaemun District, following an accident the previous day, Aug. 30. Yonhap

Meanwhile, experts urged for increased investments in preventive measures, stressing the importance of utilizing equipment such as GPR to identify potential sinkhole risks before they develop.

"With large-scale construction or underground tunneling, the surrounding ground becomes unstable, increasing the likelihood of sinkholes," said Kong Ha-sung, a professor of fire and disaster prevention at Woosuk University.

"We need to thoroughly inspect the ground before construction and strengthen weak areas in advance, and a monitoring system that detects ground subsidence during tunneling is essential."

Kong also stressed the importance of regular inspections and maintenance of aging underground pipes, adding that preemptive replacement should be prioritized based on their durability.

Lee Young-ju, professor of the School of Fire Safety at Kyungil University, pointed out the limitations of relying solely on increased equipment to monitor all roads.

"It's more effective to focus on areas at risk, such as those affected by underground construction, and monitor them proactively," he said.

Lee acknowledged that preventing all sinkhole incidents is nearly impossible but emphasized the importance of minimizing conditions that allow water to seep underground.

"When a sinkhole or road subsidence happens, swift reporting is also crucial," he said.

"Identifying the problem quickly allows for emergency repairs, which can help ensure the road remains usable and minimize further damage."