Study On Genetic Mechanism And Hazard Assessment Of Karst Collapse In Central Guizhou

Soluble rock is widely distributed in China,covering an area of 346.3 × 10 ^ 4km? 2,which accounts for more than 1/3 of the land area.The development of such a large area of soluble rock provides the necessary material conditions for the formation of karst collapse.In recent years,with the deepening of economic construction,the scope of human engineering activities is increasing day by day,which leads to the occurrence of karst collapse more and more frequently.it is a very urgent task to study the mechanism and prevention technology of karst collapse.Taking the karst collapse in Linyan Village,Zhanjie Town,Qingzhen City as an example,through the collection of geological data and field geological survey,this paper completes the collection of geological environment data,hydrogeological data and engineering geological data in the study area,and uses the combination of geophysical and drilling to reveal the karst development and distribution characteristics of the study area,and statistically analyze the distribution characteristics and laws of karst ground collapse in the study area.The genetic mechanism of karst ground collapse in the area is analyzed and studied,and finally the risk assessment of karst ground collapse in the study area is completed.The main research results of this paper are as follows:The main results are as follows:(1)the study area belongs to the covered karst area.by means of geophysical exploration and drilling,it is revealed that the karst stratum in the study area is Permian Maokou formation(P2m)limestone,and the distribution characteristics of soluble rock and karst development distribution law.It shows that the distribution characteristics of soluble rock in the study area have a certain controlling effect on the distribution law of karst development,which is verified by drilling.For the area where the buried depth of karst is shallow,the underground concealed karst caves are densely distributed,and the hole penetration rate of boreholes is 70%.For the areas with deeper burial depth of soluble rock,the underground concealed karst caves show scattered distribution,and the development scale is small.(2)through the analysis and study of the distribution characteristics and development law of karst in the study area,it is concluded that the four factors that affect the development of karst are stratum lithology,geological structure,topography and geomorphology and overburden thickness.There are mainly covered soluble rocks in the study area,which are affected by structural processes such as folds and faults,resulting in the development of rock joints and many fissures,which enhance the water permeability of the rock strata and make the dissolution reaction intense.the function of topography and geomorphology is mainly to control the flow direction and velocity,thus affecting the degree and scale of karst development,and its permeability is different according to the thickness and structure of the overlying soil layer.If the overburden with large thickness or poor permeability is encountered,the development of karst in the lower part is poor.(3)through the on-the-spot investigation of karst collapse in the study area,the distribution characteristics and rules of karst collapse points in the study area are summarized.the results show that there are two main collapse modes in the study area,the first one is far away from the Sala River.the collapse is mainly caused by vacuum suction.After the decline of groundwater,on the one hand,the soil loses buoyancy,on the other hand,the vacuum negative pressure has vacuum suction effect on the overburden soil.Easily lead to collapse.The second kind is located on both sides of the Sala River,which is mainly caused by latent erosion and vacuum suction.In the process of reciprocating rise and fall of groundwater,on the one hand,the overburden soil will be affected by the lateral permeability of the river water,on the other hand,the soil will not only lose buoyancy but also be affected by vacuum erosion,which is easy to cause collapse.(4)through the collection of hydrogeological data in the study area and the field double-ring permeability test,the relevant hydrogeological parameters are obtained,and the groundwater numerical simulation model is constructed.The groundwater dynamics in the study area are simulated and analyzed by using MODFLOW,and the changes of groundwater flow field and groundwater depth distribution are obtained.The groundwater level change of the subsidence point TX18 is simulated with FLAC3 D numerical simulation software,when karst voids are developed in the bedrock.The change of stress and strain of overburden soil in the process of groundwater decline can provide a basis for predicting the influence range of karst collapse.(5)according to the main factors affecting karst development in the study area,the factors affecting karst collapse in the study area are divided into three first-level indexes:karst development conditions,overburden conditions and groundwater conditions.there are 8 secondary indexes,such as bedrock lithology,karst development degree,distance from fault structure,thickness of overburden,permeability,fluctuation amplitude of groundwater,buried depth of groundwater and distance from pumping well.The analytic hierarchy process and fuzzy comprehensive evaluation method are used to evaluate the risk of karst ground collapse in the study area,and the risk zoning map is obtained by Arc GIS,and then the corresponding prevention and control measures are put forward according to the collapse mechanism and distribution characteristics of karst ground collapse.