Mechanism And Risk Assessment Of Surface Collapse In A Karst Mining Area In Hubei Province

Karst collapse in a mining area in Hubei Province is taken as the research object in this paper,through collecting the existing data,field investigation,geophysical exploration and other technical means,the development characteristics,distribution rules and various factors affecting the karst collapse in the study area are summarized and analyzed.The mechanism of karst collapse induced by the change of groundwater level caused by drainage and curtain leakage in mining area is studied by numerical simulation.The risk assessment model was established according to the characteristics,distribution and evolution mechanism of karst collapse in the region,the karst collapse risk zoning map in the study area was drawn,reasonable suggestions for subsequent mine treatment and engineering planning have been put forward.The thesis has the following main research results:(1)The development characteristics and distribution of karst and karst collapse in the study area are summarized.Karst is irregularly distributed in the study area,under the influence of structure.It is mostly distributed in the vicinity of contact zone and fault fracture zone,and it is mostly banded,karst is controlled by elevation and does not develop as it goes deeper.Karst collapse occurs mostly in karst development areas,and is affected by drainage and drainage in mining areas,mostly concentrated in areas with frequent changes of groundwater level.(2)The influencing factors of karst collapse in the study area are summarized and the mechanism of karst collapse in the study area is analyzed.Geomorphologic conditions,overburden conditions,bedrock lithology,geological structure and karst conditions control the karst collapse in the study area,the dynamic change of groundwater level caused by drainage is the main inducing factor of karst collapse in the study area.According to the analysis of the influencing factors of karst collapse in the study area,the geological generalization model is constructed.The main mechanism of karst collapse is as follows:The collapse caused by groundwater infiltration and the collapse caused by the rise and fall of the groundwater level.(3)Based on FLAC^3D numerical simulation software,the ground subsidence process induced by the dynamic change of water level in the subsidence area is simulated.Draw the following conclusion:When the mine drainage causes the groundwater level to drop in the subsidence area,the main factors that cause soil failure are the large difference of pore water pressure and the concentration of stress above the opening of molten rock.Under the concentrated action of seepage pressure and shear stress,the arch foot of the soil tunnel is damaged,which leads to the expansion and development of the soil tunnel,as the failure continues to develop upward.The soil at the roof of the cave will be tensile failure,and the failure will extend to the surface and finally form the ground collapse.When the lower water level rises,the soil above the soil hole will be softened by strain under the action of water,resulting in stability destruction and collapse.(4)Through the study on the formation mechanism and numerical simulation of karst collapse in the study area,combined with the factors affecting the karst collapse such as landform,groundwater dynamic change and karst development characteristics,by combining AHP and Arc GIS.The karst collapse in the study area is divided into dangerous areas of varying degrees.The prevention and control measures of karst collapse have been put forward,and the research results have practical significance for the prevention and control of geological disasters of ground collapse in mining areas.