A man in his 30s who was buried in a sinkhole accident near the entrance of Daemyung Elementary School in Myeongil-dong, Gangdong District, was found in cardiac arrest by the fire authorities around 11:22 a.m. on the 25th. He fell into the sinkhole while riding a motorcycle at around 6:29 p.m. on the 24th, approximately 17 hours earlier.
Director Kim Chang-seob of the Gangdong Fire Station said during a briefing that Mr. Park, 33, was found wearing a helmet and motorcycle boots, just as he was when he fell into the sinkhole. The motorcycle Mr. Park was riding was discovered inside the sinkhole around 3:32 a.m. on the same day. Earlier, around 1:37 a.m., a mobile phone presumed to belong to Mr. Park was also found.
The newly formed sinkhole measures 20 meters in diameter and 18 meters deep. As a result of the sinkhole, Mr. Park fell, and shortly before that, the driver of a white Carnival vehicle, Mr. Heo, 48, who passed the scene, sustained minor injuries and is receiving treatment.
When the sinkhole first formed, it was approximately 18 meters wide and 20 meters long, covering four lanes. As time passed, its width increased by about 2 meters. The depth of 18 meters measured is not only the pit where the road collapsed. Below the accident site, excavation for the extension of Seoul Subway Line 9 was underway, creating a tunnel. The pit itself is 11 meters deep, and below it, the tunnel ceiling collapsed, causing soil to accumulate. The tunnel depth is 7 meters, making the total depth 18 meters when the pit and tunnel depths are combined.
In the underground construction area where the subway work was being conducted, approximately 6,480 tons of soil accumulated over an 80-meter section of the tunnel. Underground, there are water pipes, which were damaged the previous day, causing tap water to gush out and complicating the search operation. The fire authorities removed about 2,000 tons of water using a drainage pump and then deployed two excavators to remove the soil while searching for the missing person.
The missing motorcycle driver, Mr. Park, was found about 50 meters from the center of the sinkhole, buried under 90 centimeters of soil. The mobile phone was 40 meters away, and the motorcycle was 20 meters from the sinkhole. The motorcycle was also covered by about 80 centimeters of soil.
The fire authorities initially faced difficulties in the search operation due to a mixture of water and dirt. Director Kim Chang-seob of the Gangdong Fire Station noted, 'At first, (the soil) was mixed with water, so we started working by hand with shovels, but now heavy equipment (excavators) is being used to scrape from the bottom.'
The fire authorities lowered two excavators into the tunnel floor from the entrance of the subway construction site using a crane and then moved them to the location where the soil was piled up. After that, they removed the heavy equipment previously used in the subway construction and began the search for missing persons while excavating the soil.
However, the fire authorities are taking a cautious stance regarding whether the subway construction and water pipe breakage are the causes of the sinkhole. Director Kim stated that regarding the cause of the sinkhole, 'we need to investigate assuming various scenarios.' Lee Jae-hyuk, head of the Urban Infrastructure Division of the Seoul City Metropolitan Rapid Transit Construction Department, stated during a briefing at the scene that they 'do not rule out the possibility of a correlation with the subway construction,' adding, 'We will have to conduct a thorough analysis in the future to determine the cause.'
Just before the accident occurred, subway construction work was still ongoing. Director Kim said, 'There were about 4 to 5 workers in the subway construction site. They noticed the signs of the sinkhole and evacuated immediately, so they were not harmed.'