A 2.5 m wide and 5 m deep sinkhole opened in a road around 1 km away from the construction site of an amusement park in Songpa district in southern Seoul on Tuesday.
It was the fifth sinkhole in the district this year. No one was hurt.
The Seoul metropolitan government believes the sinkholes may be related to construction of the controversial second Lotte World shopping mall and amusement park, which has already seen a couple of accidents and raised fears that its height could mean trouble for a nearby airport.
The first sinkhole formed adjacent to the construction site on June 29, and three more were discovered on June 30 and July 4 and 21.
An official at the district office said, "The first four sinkholes appear to have formed after water seeped out of damaged sewage pipes or leaking water mains that eroded the earth."
But the latest sinkhole looked different and was significantly deeper. A Seoul city official said, "We're investigating the possibility of damaged sewage systems or weakened foundations due to subway construction, but we can't rule out that it's got something to do with the construction of the second Lotte World."
Chung Choong-ki at Seoul National University said, "Large construction projects can lower the levels of underground water tables, and the weakened buoyancy raises the weight carried by the ground. But sinkholes can also form if water pipes are damaged."
Lotte denies any responsibility. Lotte Engineering and Construction spokesman claimed investigations have shown that the last four sinkholes in the district "had nothing to do with the construction project… and the latest one is a long way from the construction site."