Mechanism Of Karst Collapse Of Xinjian Of Fenggang County,Guizhou Province

With the development of social economy in Guizhou, the karst collapse has occurred, which has a significant impact on the national economic construction, and has become one of the main geological disasters. Therefore, the research of mechanism of karst collapse and prevention technology is a very important subject. The paper takes the karst collapse of Xinjian of Fenggang County as an example, and the environmental, hydrological and engineering geological conditions of the collapse area were analyzed. The karst development regularity and the conditions of karst hydrodynamic were main research contents. On the basis of this study, the spatial and temporal distribution characteristics of karst development, the characteristics of red clay and the dynamic conditions of karst water are analyzed emphatically. Then, The mechanism of karst collapse were analyzed, and results of analysis and research has been made as follows:(1) The study area is the covered karst, the stratum of the study area is the Loushanguan Group of Cambrian and the stratum have experienced many tectonic activities in the past for a long time,so the direction of karst development is controlled by faults of two directions of 30°~70° and 310°~320°. There are depressions or channellings arranged as a string of beads and the karst cave or solution cavity distribute at 775~805m, and the hole rate is 50%. Red clay thickness variation rang 2m to 10 m, and the status of red clay changed from the plastic state to the soft plastic state, and the strength changed lower. The research area is in the upper stage of Anti equilibrium profile of karst hydrodynamic, where the groundwater is buried shallow and the water level changes 4~10m, and the soil is eroded strongly. The macro-crystalline dolomite will become dolomite karst sandification produced by dissolution and increase hole formation and collapse. The development of karst collapse in the area has caused, under the background of the unique karst geological environment.(2) The collapse mode of the study area is as follows:(1) collapse due to loss of support(the underground water level is repeated up and down, the potential erosion action, the rock and soil loss),(2) the repeated collapse(the treatment of the collapse is not in place).(3) Calculation and analysis show that collapsing stress was buoyancy generated by 3.5m to 5.5m groundwater, selected nine collapse of study area, by using mechanical model—?0h+Pt+?P=(k0?0h2tg?+2ch)/r. So the karst collapse occurred when the groundwater decreased rapidly after soil lost buoyancy of groundwater.(4) Soil stress and displacement in the erosion process were simulated by using Mohr-Coulomb Model in FLAC-3D, and the results of simulation are close to the reality.(5) Simulation and analysis of the mechanism of karst collapse was obtained by using mechanical method and three-dimensional numerical simulation method, this study provides a reference for the objective evaluation of karst collapse geological disasters and the prediction of early warning.