Sinkhole Hazard Assessment Based on Real-Time Monitoring of Karst Water Pressure in Guangzhou, China

Since July 14, 2007, more than 20 sinkholes formed at Jinshazhou, Guangzhou, the largest city in southern China. Draining water during the construction of the Jinshazhou tunnel of the express railway between Wuhan to Guangzhou was thought to induce these sinkholes. The primary goal of this project is to assess the risk of potential sinkhole collapses around the tunnel area. Seven piezometer wells were installed in the study area to monitor changes of karst water level. The critical hydraulic gradient (I₀) that may trigger sinkhole collapses was determined through seepage deformation tests of undisturbed soil samples collected in the study area. From October 18, 2007, tunnel construction resumed. Monitoring results demonstrated that karst water level at site #19 had declined 12.69 meters from October 18 to October 25, 2007. It was approximately 4.79 m below bedrock surface and this area has the highest risk of potential sinkhole collapses. Hydraulic gradients (I) at all seven monitoring sites were greater than the critical value (I₀), which means seepage deformation could occur at the soil layer above karst bedrock. Because the overlain soil and sediments were altered by the sudden change of karst water level, the risk of sinkhole collapses could last for a few years, even during the slow recovery of karst water level after the completion of tunnel construction. The monitoring method described in this paper could benefit site selection and decision making processes during railway construction in other karst areas.