Different Types and Formation Mechanisms of Karst Collapse in Huainan City

Karst collapses have been occured ,which brings potential geological hazard for the risk of construction of mining cities and the ecological environment restoration. By the methods of field geological survey, statistical analysis and numerical simulation methods, the characteristics and distribution of karst collapses have been investigated systematically along such areas as Shungeng Mountain, Liyingzi,Tubazi,and Fengtai County, and the formation conditions and types of karst collapse are discussed, and the formation mechanisms are simulated under different conditions.The results show that influenced by the combined actions of stratigraphy, lithology, geological structure and hydrogeological conditions, karst collapses mainly develop in the Ordovician and Cambrian strata covered with the unconsolidated sediments, which is distributed concentrately along the strikes of strata and near fault tectonic zones. Based on hydrogeological conditions, dip of strata, and induced factors, karst collapses can be classified into four types:steeply dipping, gently dipping, overturned under dewatering conditions, and the variable load of overlying soil. In order to understand the formation mechanism of karst collapses, FLAC ^3D software is used to simulate and analyze the variation about displacement and effective stress at different designed observed points ,along vertical cross section covered with unconsolidated sediments during the processes of dewatering in coal mines and urban construction. The study of formation process of karst collapse provides important guidance for the prevention and control of karst collapse disasters.