Formation Mechanism And Numerical Simulation Studies Of Karst Collapse In The Tailai Basin,Shandong Province

The Tailai Basin is located in the middle of Shandong Province.The soluble rocks in the area are widely distributed,and the temporal and spatial changes of precipitation are relatively large,resulting in large fluctuations in the groundwater level.By a cover layer Quaternary sediments,and configured to provide a good impact and occurrence space groundwater transport channel,these geological environment facilitated collapse,so that frequent karst collapse study area,destroy buildings,affecting traffic and destroying farmland,seriously threatening people's lives and property.Although a large number of investigations and studies have been conducted on the karst collapse of the area before,there is a lack of quantitative research on the stability of karst collapse.In this paper,according to the status of karst collapse in the Tailai Basin,the geological model of the typical subsidence area is generalized,the causes of formation and the mechanism of evolution formation are established.On this basis,the numerical model is built using flac3d software and the stability warning of typical areas is carried out.Based on previous research results collected,combined with the actual survey data,this article summarizes the geological environment conditions in the study area and the status quo and hazards of the collapse research in the Tailai Basin.The area of subsidence within the area is widely distributed.Multiple subsidence areas are still in the stage of frequent collapse.The subsidence is mainly distributed in the following areas:1 Tai'an City's urban area and old county water source area;2 Laiwu Iron Mine District Menggong County,Mengjiazhuang,Xiquanhe area;3 The dry river area of Gushan-Zhaili Town,Dawangzhuang Town,Laicheng District,Laiwu City.In addition,there are sporadic distributions in the Qiaogou and Bianjiazhuang areas in the town of Tai'an City Culai bridge ditch area,Tai'an City,and Pengshan Water Source Area and the Qingnigou Water Source Area in Laicheng District,Laiwu City.The frequent occurrence of subsidence has caused damage to infrastructure facilities such as railways and highways,farmland,residential buildings and groundwater.By analyzing the characteristics of the typical subsidence areas and the causes of subsidence,three types of geological models,ie,monolayer structure model,double-layer structure model and multi-layer structure model,were established.The main mechanism of action was analyzed for the three geological models.In the single-layer structure,the initial soil hole was formed by vacuum erosion,and then a collapse pit was formed under the combined action of groundwater and the like;In the double-layer structure,the initial soil cavity is formed by the infiltration deformation,and the hole continues to develop under the influence of many factors,eventually forming a collapse pit;In the multi-layer structure,the initial soil cavity is formed by vacuum erosion,and the soil cavity is developed upwards and extended to the sand and pebble layer.Under the effect of seepage,the soil particles undergo latent erosion and eventually cause collapse.On the basis of the above research on the Tailai Basin,we selected two typical regions to build a model,selected a single-layer structural model for the Yujiaguan village,and selected a double-layer structural geological model for the collapse zone of the Yanglou.According to the calculation results,the degree of development of soil caves in a single-layer clay structure has a greater influence on the stability of the model,while the effect of the penetration is smaller.For the double-layer structure,when the lower layer is medium coarse sand,the effect of permeation on the stability of the model is greater,and the shear strength is relatively poor.Under the percolation effect,the shear strength is further reduced;at the same time,the increase in the thickness of the cover layer is conducive to stability,and vice versa.According to the model calculation results,the stress distribution change,displacement change,plastic zone change,and stability coefficient value of the model are analyzed to determine the stability of the soil layer and determine the critical safety soil hole.When the soil moisture content is higher,the thickness of the clay layer in the single-layer soil structure is 8.5m,and the critical safe soil hole radius is 0.46m;In the double-layer structure,the thickness of the clay layer is 5.5m,medium coarse sand is 8.5m,and the critical safety hole radius is 0.44m.According to the critical safe soil hole size calculated in the model,geophysical exploration methods are used to survey the caverns and detect the size of the caverns in the subsidence area.If the cavern radius in the subsidence area is not more than 0.46m in the safe soil cavern radius,it will be stable,otherwise it will be the other way around.In the double-layer structure,if the radius of the cavern in the subsidence area is not more than 0.44m,the radius of the safe soil cave will be stable;otherwise,it will be the opposite.Based on the formation mechanism and numerical simulation of karst collapse in the Tailai Basin,this paper quantitatively analyzes the stability of the subsidence area and provides decision-making basis for the prevention and control of geological disasters in the karst collapse of the Tailai Basin.The research results have practical significance for the prevention and control of geological hazards.