Research on the reason for geologic disaster by karst surface collapse at Jinshazhou in Guangzhou

As one of the most serious karst collapse areas in Guangzhou City, there are 24 collapse spots at Jinshazhou. The collapse spots mainly distribute on the sides of a high speed rail tunnel with the vertical distance from the tunnel less than 400 m. The formation and development of collapses have close relationship with fragile geologic environment and high-speed rail tunnel construction. According to the survey, NE trending fault is quite developed at Jinshazhou, revealed hole-rate between ranges from 60 % to 76.9 % in concealed limestone, the linear karst-rate is up to 52.58 %, the thickness of the overlying earth on some sections of limestone is less than 15 m. Drainage is strong during the construction of high-speed rail tunnel. The amount of pumping groundwater comes up to 2 000～3 000 m 3 /d, which leads to groundwater table severely fluctuates and results more than 20 collapses. There are no collapse occurred when the tunnel stop pumping. The development characteristics of karst collapse shows that fragile geologic environment is the inherent factor leading to karst collapse at Jinshazhou, while the high-speed rail tunnel pumping is a predisposing factor direct leading to collapse.