Construction of mechanical model of water inrush from water-rich confined karst cave in coal seam floor and study on criterion

Important coal production bases in the southern part of the country are mainly located in Southwest China,where the karst landforms are widely distributed and the karst are strongly developed. And there are also many water-rich karst caves in the limestone of Maokou Formation in coal seam floor,which are main mining strata in this area. Once the water-rich karst caves are encountered in the process of coal mining,the water resisting rock of coal seam floor is prone to instability and failure under the dual pressure of mining and confined water,resulting in water inrush disaster,which poses a serious threat to the safety of coal mining. In order to study the geological controlling factors and the mechanical behavior of instability and failure of water resisting rock when the water inrush disasters of water-rich karst caves in coal seam floor occur,and to effectively guarantee the safety of coal mining,the karst cave roof was simplified as a circular section,and the water resisting rock between the karst cave and the coal seam was simplified as a conical platform model composed of countless integral thin circular plates based on the morphological characteristics of karst cave and stress characteristics of water resisting rock in Southwest China. And then a mechanical model of water inrush from water-rich karst cave in coal seam floor was constructed. The cusp catastrophe model in catastrophe theory was used to analyze the mechanical model,and the standard potential function expression of system deformation and instability was obtained based on the theory of elasticity. The critical stable state of the system was obtained,and the mechanical criterion of water inrush from water rich and confined karst cave in coal seam floor was deduced. The study showed that the instability and breaking of the water resisting rock which cause the water inrush disasters of water-rich karst cave in coal seam floor was mainly controlled by geological factors such as the thickness,the elastic modulus,the Poisson′s ratio of the rock layer,the size and the water pressure of the karst cave. And the smaller the thickness,elastic modulus and Poisson′s ratio of the water resisting rock,the larger the karst cave size and the greater the karst water pressure,the more likely the water inrush disasters would happen. Achievements can provide a scientific basis for the explanation and prevention of water inrush from karst caves in coal seam floor. 