Development characters of karst collapse in the Gele mountain area

The trough valley zone of the Gele mountains is largely covered by limestone, with a hill landform and complex geological environment. Influenced by the subtropical monsoon climate, the rainfall of the rainy season (from May to October) in this area reaches 881.40 mm, accounting for 80 percent of the total annual precipitation, resulting in nonuniform distribution of rainfall between the rainy and dry seasons. With the increasing human engineering activity in recent years, karst collapse occurs frequently, which have become the main geological disaster in this region. This work collected and analyzed relevant data of previous surveys and related data of existing hydrological boreholes with long-term observations, and made a special investigation of environmental geology and geological disasters on scales of 1∶2 000～1∶10 000. The purpose was to determine the number and distribution of karst collapse and human engineering activity status in this region. The survey area is 60 a.km2. The results show that the number of karst collapse has an increasing trend year by year, which are mainly distributed in those places where the karst developed well, the groundwater level changed significantly, more calcium carbonate are present, and the thickness of the loose cover ranges from 3 to 8 meters. It divided the process of collapse development into early stage, middle stage and late stage and analyzed the characteristics of these developmental stages. By analysis of the types and function of collapse forces in the process above, it suggests that the latent erosion is the primary mechanism for the collapse. To sum up, the number of karst collapses increases year by year, which mostly occur in rainy seasons. There is an obvious characteristic pattern of spatial distribution as well as stage-wise development of karst collapse, and the latent erosion is the dominant mechanism.