November 9, 2016 6:05 am JST

Giant Japanese sinkhole blamed on tunnel work

A large sinkhole swallowed up this roadway Tuesday in Fukuoka, Japan.

FUKUOKA, Japan/TOKYO -- Businesses lost power and traffic had to be diverted Tuesday after a huge sinkhole swallowed part of a busy intersection in the southwestern Japanese city of Fukuoka.

The cave-in began around 5:15 a.m. near JR Hakata Station, a major rail hub for the region, eventually developing into a pit 30 meters long, 27 meters wide and 15 meters deep. Underground electrical and gas lines were severed, cutting off power to as many as 800 customers. Surrounding buildings lost gas service.

Some online banking systems experienced outages. One woman in her 70s suffered minor injuries from a fall during the blackout.

City officials are pinning the cause of the sinkhole on a project to expand the city-run subway. Veins of groundwater crisscross the port city. Something appears to have caused water and soil to burst through a layer of clay and flow into a subway tunnel under construction, weakening the ground holding up the road.

This is the latest in a string of ground collapses occurring throughout the country, with groundwater emerging as a recurring cause. Other sinkholes sharing that characteristic formed in Tokyo in 2012 and 2015.

"Japan is rich in groundwater, and the same type of disaster can occur anywhere," said Satoru Shimobe, professor at Nihon University. "Construction projects require careful ground surveys."

A large-scale sinkhole caused by rail construction occurred in 1990 in Tokyo. Engineers were extending the Tohoku Shinkansen bullet train line when the roadway above the tunnel excavation caved in, injuring around 10 people. It was later found that workers failed to inject enough hardening agent into the ground.

Recent years have seen sinkholes caused by aging water pipes. About 3,300 such cases occurred in fiscal 2014, data from the transportation ministry shows. They most frequently occur in urban areas, which often have the oldest sewage systems.

"Sewer pipes, subways and other urban infrastructure are aging, and the risk of cave-ins is growing," said Takashi Matsushima, professor at the University of Tsukuba. "Local governments and businesses need to perform thorough inspections."

(Nikkei) 

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