Mechanism analysis of sinkholes formation at Jili village, Laibin City, Guangxi, China

After an extreme rainstorm event in June 2010, 17 sinkholes emerged at Jili village, Laibin City, Guangxi in a month. The impact area occupied more than 1,500 m2. Three of the sinkholes expanded and merged gradually and eventually developed into a large sinkhole which is 170 m long and 38 m deep. It is the largest sinkholes in Guangxi. In order to understand the formation mechanism, extensive investigations including field investigation, three-dimensional laser measurement, geophysical prospecting, exploratory boreholes and real-time monitoring of karst water pressure and rainfall were conducted. The results indicated that sinkholes at Jili village were attributed to natural factors ,which is the result of multiple adverse factors. These factors mainly include the special "water-soil-rock" combination and extreme rainstorm. The special geological conditions determine the particularity of the sinkholes. Analyzing the formation process and mechanism of the sinkholes, we think they were mainly controlled by the combination of gas explosion effect, water hammer effect and seepage erosion effect.