A team of experts from the Seoul metropolitan government tentatively concluded last Friday that a mistake during the tunnel boring process for Subway Line No. 9 led a massive 80 m-long sinkhole beneath an underpass in Songpa district in southern Seoul.
Park Chang-kun, a professor of civil engineering at Kwandong University who heads the team, said, "The sinkhole in the Seokchon tunnel opened because nobody prevented the nearby earth from crumbling when they bored the tunnel."
The construction company in charge is Samsung C&T Corporation.
All six large and small sinkholes, which were discovered in the Seokchon tunnel from Aug. 5 to 18, were created the same way, Park added.
The Seoul metropolitan government is expected to announce the team's final conclusion and the city's solution early next week.
Samsung says it is waiting for the final report.
Dr. Yoon Tae-kuk of the Korea Infrastructure Safety and Technology Corporation said, "I don't think Samsung can shirk responsibility, because it won the project on a turnkey contract."
But Samsung's woes mean relief for the Lotte Group, as initially construction of the super-high Lotte World Tower nearby was being blamed.
"It proves we are innocent as we have said based on objective, concrete data on the construction of the tower," a Lotte executive said.
Meanwhile, the wheels of a van sank into a separate sinkhole in the middle of a road near the Seoul National University of Education in Seocho, Seoul.
This sinkhole was 1.8 m long, 1.3 m wide, and 1.5 m deep. There were no casualties, but nearby roads were blocked for some time.
A Seoul city official speculated, "The sinkhole in Seocho seems to have something to do with leaking water or sewer pipes," which eroded the surrounding soil.