Chasms prompt city into action

The Seoul city government will put 220 billion won ($216 million) next year toward repairing old sewer pipes and strengthening the monitoring of tunnel excavation and construction in a push to prevent urban sinkholes and underground cavities.

A series of chasms found beneath and around Seokchon Underpass in Songpa District, southern Seoul, were induced by poor underground construction and development practices, the Seoul city government said yesterday in its conclusive report on the cause of the hazardous formations.

The announcement was a blow for Samsung C&T, the builder conducting underground tunnel construction to make room for an extended section of subway line No. 9.

The vice president of the construction company, who attended the press briefing, said that it will respect the result of the inspection and follow through with measures to prevent any further cases.

“I would like to apologize to the public for causing concern,” said Vice President Kim Hyung.

A special investigation team, comprising 23 geology experts, started its probe by drilling at the construction site earlier this month after an 8-meter (26.2-feet)-long underground cavity was found on Aug. 5 near Seokchon Station, southern Seoul.

The head of the special investigation committee said that Samsung C&T excavated approximately 3,317 cubic meters (4,338 cubic yards) more soil than planned for the construction, which significantly weakened the earth and led to the empty pockets as well as the sinkhole. “We learned that Samsung C&T removed more soil than stated on their construction blueprint,” said Park Chang-geun, who led the investigation.

The practice is particularly hazardous when taking into account the geological conditions of the underground area. Some parts of Songpa District were reclaimed in the 1970s and filled in with more sand and gravel than found in the typical underground terrain. The underground composition is more at risk for soil erosion and generally less stable with less solid rock.

“It is basic knowledge that a builder should take a particular concern for the amount of soil excavated and other general construction practices when doing underground work in this type of terrain,” Park said. “However, the inspection revealed that the company did not pay full attention to reinforce the ground.”

The Seoul Metropolitan Government also came under fire for not properly overseeing the construction.

The municipal government distanced itself from the underground project, saying that the construction was being done under a turnkey contract, in which the builder is mainly in charge of finishing a project, while the owner or operator has limited authority or say.

However, the city government stressed that it is partly responsible for the mishap and will come up with a set of measures to prevent such formations. As part of the plan, Seoul will spend 220 billion won next year to refurbish its sewer system. The amount is 100 billion won more than this year’s allocation.

Despite the fact that the cavities around Songpa District were determined to have been caused by underground construction methods, the Ministry of Environment also pinpointed the older sewer system as a reason for the hole formations in other regions. Seventy-three percent of Seoul’s 10,297-kilometer sewage system is more than 20 years old.

The municipal government also vowed to appropriate more sophisticated equipment to track geological conditions, along with an extensive mapping system that would detail the structure of the terrain and the locations of any holes.

BY PARK EUN-JEE [ejpark@joongang.co.kr]