A large sinkhole that appeared 350 meters south of subway Line 4's Tiangongyuan Station, in Daxing district, is the most recent land subsidence to occur in close proximity to Beijing's subway system.
Workers were using a backhoe to remove dirt from the hole when the Global Times arrived at the scene at around 1:30 pm on Monday.
The sinkhole, which formed Sunday, was about 5 meters deep, 30 meters long and 15 meters wide, completely blocking access to Xinyuan Dajie. However, local traffic was not affected because traffic volume in the area is minimal.
"Heavy rain [last Thursday] made the road collapse," a road worker surnamed Wu told the Global Times, adding that Xinyuan Dajie had already developed several sinkholes due to a water pipe leak about 20 days earlier.
A 200-meter-long section of the south-to-north lane of Xinyuan Dajie was sealed off on Monday for repairs, and about five other small holes two or three meters in diameter had already been filled with cement. Another big sinkhole about 3 meters deep had not been properly filled as of on Monday afternoon, and part of the lane's surface had also been stripped for repairs.
"The fact that subway trains run beneath Xinyuan Dajie might have something to do with the sinkholes," an employee of Beijing Xingchuang Investment Company Limited, which built the road, told the Global Times on Monday.
"It is complicated. We are analyzing the case now, and it would be irresponsible for me to say anything," an employee of the company's engineering department who would not give his name told the Global Times.
The Daxing district Commission of City Administration issued a public notice on May 26 saying that the administration would use radar to detect potential safety hazards beneath Xinyuan Dajie and to ensure smooth subway operations.
The Global Times has reported on several subsidence cases in close proximity to subways or subway construction sites this year. The deepest sinkhole swallowed a truck outside the Shiliuyuan Nanli community in Fengtai district, 200 meters from the construction site of subway Line 10's phase two project.
"A road will sink if the ground below has become hollow, no matter how well built the road is," Wang Qingwen, spokesman of the Beijing Municipal Commission of City Administration, told the Global Times on Monday, without speculating on the specific cause of the recent subsidence cases.
With today's technology, subway structures should not cause land subsidence, according to Wang Mengshu, a subway expert and member of the Chinese Academy of Engineering.
"The sinkholes are caused by other things," Wang Mengshu said. "For example, some courtyards do not have proper toilets and sewer systems, so residents dig wells to discharge all their waste, compromising the ground's hardness."
However, Cai Xiangmin, president of the Beijing Institute of Geological Survey, was not ruling anything out, saying that both geological conditions and underground construction projects can cause sinkholes.
"The situation of each sinkhole case is complicated and requires further study," Cai told the Global Times on Monday, adding, "but if you follow the news and check the locations of the sinkholes, you will find a pattern and can see where road sinkholes occur most often."