Sep 03, 2012 03:37 PM

Sinkholes a Growing Problem in Urban Areas, Say Experts


A 15-meter wide sinkhole appears in Xi'an, Shaanxi Province, with a depth of 6 meters

(Beijing) – China's megacities are developing a growing number of sinkholes and experts say a combination of aging water pipe networks and underground infrastructure projects are raising the risk of sinkhole disasters.

On August 14, an 8-year-old girl named Lin Yuetong and a woman named Sun Shuying died after plunging into a 10-meter diameter sinkhole in Harbin, Heilongjiang Province.

At the time, Lin was playing in front of a supermarket with her grandmother. Sun was also nearby the market, carrying her baby. Suddenly, four people fell into a sinkhole that opened up to become 13 meters deep. The two people that survived were severely injured. 

Over the course of roughly one week, the city of Harbin recorded six other incidents of sinkhole collapses. While no other fatalities were reported, the sinkholes destroyed several cars.

Sinkholes are geological depressions typically caused when the stability of underground sediment is eroded by water or other factors. In urban environments, sinkholes can occur around leaky water pipes that wash away silt.

Assistant engineer Song Guchang, of the Beijing General Municipal Engineering Design & Research Institute, wrote in a paper that in Beijing alone there were 54 sinkhole collapses in 2007, 94 incidents in 2008 and 129 in 2009. More recent official statistics have not been made available.

Just this year, 99 sinkhole collapses occurred in Beijing between July 21 and August 12, according to statistics from a bridge maintenance company.

Beijing's underground infrastructure is dominated by the presence of bomb shelters beneath the city. Researcher Ma Zhifei, of the Beijing Institute of Geology, said there are an estimated 20,000 shelters in the capital. Poor maintenance of the facilities contributes to the increasing number of sinkholes.

Experts said that the recent rise in the number of sinkholes has sparked growing concern over road and infrastructure defects in urban areas.

Wang Mengshu, a member of the Chinese Academy of Engineering, said poorly planned underground infrastructure project are a major contributing cause of sinkhole collapses. Projects that destabilize the ground are becoming a safety concern in densely developed areas.

Underground infrastructure projects can significantly affect the stability of nearby high-rise buildings, said Sun Jichao, a researcher at the Chinese Academy of Geological Sciences.

Twenty years ago, Japan was faced with the sudden emergence of sinkholes in cities such as Tokyo and Nagoya. Hiroshi Tomita, CEO of technology service company GeoSearch, said that Tokyo once saw as many as 20 sinkhole collapses per year. Since increasing inspections of underground terrain with radar, the city now sees roughly two collapses per year.

Wang said urban planning authorities in China must allocate more resources to mitigating sinkhole risks and the tougher enforcement of building regulations.

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