On March 24, a 20-metre-wide and 18-metre-deep sinkhole formed in Gangdong-gu, eastern Seoul. -- PHOTO: REUTERS
SEOUL (The Korea Herald/ANN): The Seoul Metropolitan Government announced on April 27 that it will introduce a ground subsidence monitoring network to prevent further sinkhole accidents.
Safety accidents involving sinkholes have drawn attention recently, after a 20-meter-wide and 18-meter-deep sinkhole formed in Gangdong-gu, eastern Seoul, on March 24, swallowing a motorcyclist who was declared dead the day after.
As numerous sinkhole sightings have been reported since, public concern over the phenomenon has grown significantly, with up to 50 locations in the capital city alone identified as at risk of sinkhole formation.
The new ground subsidence monitoring network, according to the city government, involves installing a bat-shaped column sensor 20 m underground. The sensor’s antenna detects changes in geological layers within a 50 m radius and transmits the information to the central monitoring station. If anomalies are identified, appropriate measures will be taken by the authorities.
This is also an upgrade from the Ground Penetrating Radar system previously used by the city government, which emits high-frequency electromagnetic waves from the surface into the ground to detect sinkholes based on the reflected signals. Though the GPR system has been used nationwide, it is effective only up to around 2 m underground.
By May, the Seoul Metropolitan Government stated that it would install the new monitoring network at a construction site located near the site of the large sinkhole that formed in late March.
At the time of that accident, construction work was underway near the site to extend Seoul Subway Line No. 9, which the city government suspended, noting that the project could not be ruled out as a possible cause of the sinkhole.
As most large sinkholes begin to form 10 meters underground, the new monitoring network is seen as a more effective way to prevent sinkhole accidents while overcoming the limitations of GPR surveys.
However, the new ground subsidence monitoring network is not a perfect solution. While GPR systems can be moved throughout Seoul on vehicles, the monitoring network can only take measurements in specific locations where sensors are installed.
Due to such limitations, the city government added that it will install the ground subsidence monitoring network system at large construction sites like the one in Gangdong-gu while expanding GPR surveys for other major excavation sites.
Separately from the city, the central government included 2.27 billion won (S$2.08 million) in its supplementary budget to support ground exploration efforts.
However, it is unclear whether such spending will be effective, as even with additional equipment purchases, the limited depth of exploration reduces the overall effectiveness of these measures. This is because most of the sinkholes discovered so far have formed near large construction sites, where machines dig deep underground.
The central government will use part of its budget to invest in GPR systems.
Aware of the technical limitations, the government considered introducing GPR systems that penetrate deeply underground - though the plan fell through earlier this year due to concerns that its performance had not yet been sufficiently verified. -- THE KOREA HERALD/ASIA NEWS NETWORK
