Analysis of karst collapse susceptibility in Guang-Fo-Zhao regions

With the rapid development of social economy, the problems associated with karst environment and geology in China are becoming more and more prominent. Karst collapse is one of the main geologic hazards in the southern covered karst areas in China. The karst collapse frequently occurred in Guangdong Province, especially in Guangzhou, Foshan and Zhaoqing City (Guang-Fo-Zhao regions), where covered karst is widely distributed. The karst collapse history in the Guang-Fo-Zhao regions is closely related to the social and economic development, which can be divided into three stages, the first stage is from 1970s to 1980s, with shallow groundwater intensive extraction. During the period, a large number of karst groundwater was extracted, which induces karst collapse in many water sources. The second stage is from the 1990s to the beginning of this century, with a large number of limestone mines mined in the open pit. The balance of groundwater is severely damaged by excessive drainage in limestone mining, which leads to the frequent occurrence of ground collapse. The third stage is from 2003 to the present, with the leap-forward development of urban construction. The constructions of underground space and building foundation have been carried out in an all-round way. In view of the great threat of karst collapse to the lives and property of the local people, it is necessary to evaluate the susceptibility of karst collapse in Guang-fo-Zhao regions, so as to provide support for land planning and disaster prevention, then so as to avoid casualties and economic losses caused by karst collapse. Based on the results of regional geological survey, according to the geological conditions of karst collapse, 9 evaluation factors are selected including density of karst collapse, karst rock stratum type, the average rate of karst, soil thickness, soil structure, groundwater type, hydrous quality, fault density and land utilization, and the susceptibility evaluation prediction model is established. The analytic hierarchy process (AHP) is used to establish the weight of the evaluation factors. The evaluation factors are classified according to influence on karst collapse. Furthermore, the susceptibility of karst collapse in Guang-Fo-Zhao regions is evaluated. The results show that the high susceptibility areas are mainly distributed in Guanghua basin, Sanshui basin and Zhaoqing area karst area, which is 1,231.96 km2, accounting for 54.48% of the total area of karst. Human engineering activity is intense in this area. Medium susceptibility areas are accounting for 15.04% of the total karst area; low susceptibility areas are accounting for 30.48% of the total karst area. According to the karst collapse zoning susceptibility areas, the karst collapse susceptibility zoning atlas of major infrastructure has been compiled. The distribution of the highway, high speed railway, the oil pipeline, the gas line and other important infrastructure in the high susceptibility areas are counted.