| The continuous development of "the Belt and Road" has also promoted the economic development of our country,and has provided a new opportunity for the development of Southwest China.The unique geographical location of Southwest China provides many opportunities for construction and development,and the karst development in southwest China,which accounts for a large proportion of the area,makes the infrastructure construction face many problems and challenges.In the actual construction process,the safety problems caused by the geological problems such as the stability of foundation pit slope being destroyed and karst collapse often occur.Therefore,it has important economic and social benefits to study and analyze the geological problems affecting the stability of foundation pit slope in Karst area,and to study the treatment countermeasures of possible karst collapse,so as to ensure the quality and safety of Engineering construction.The karst development in Guangxi is an important part of the karst development in southwest China.There are many types of karst development in Guangxi.Based on the background of karst development in Guangxi and combined with the basic situation of karst development,this paper analyses the karst problems affecting the stability of foundation pit slope from three aspects: karst development mechanism,influencing factors and karst cave classification,focusing on the influence of shallow karst caves on the stability of foundation pit slope.Shallow-buried caves are small in scale.According to the relationship between the size and depth of caves,the rock mass between the hidden caves and the slope of the foundation pit is simplified into a fixed-support model and a cantilever model.Considering that there are many factors leading to the instability of rock strata,the failure mechanism of rock mass of foundation pit slope is analyzed by cusp catastrophe theory.The potential function of critical rock mass between karst cave and foundation pit slope is established based on cusp catastrophe theory.The formula for calculating the safe thickness of rock strata is deduced,and the criterion for judging whether the treatment of hidden karst cave around foundation pit slope or not is put forward.According to the formula for calculating the safe thickness of rock stratum,it can be seen that the factors affecting the stability of foundation pit include unloading of foundation pit,karst water pressure,physical and mechanical properties of rock mass,shape and spatial location of karst cave,etc.Based on the slope engineering of the foundation pit of "Guidong Square" in the karst area of Guangxi,this paper carries out numerical experiments by using ANSYS finite element software,and studies the influence of karst water pressure,rock thickness and space location of karst cave on the excavation of vertical slope of foundation pit.The results show that karst water pressure accelerates the destruction of karst caves,and the influence on the stability of foundation pit slope decreases or even disappears when the thickness of rock stratum is large enough.When the karst caves are located in different positions,the characteristics of the influence on the deformation of the vertical slope of foundation pit are different.The deformation of the vertical slope of the fixed-supported beam model is relatively stable around the middle interface of the fixed-supported beam,and the maximum deformation position of the cantilever beam model is with the rock.The thickness of stratum is sensitive to the change of karst water pressure.According to the analytic solution and numerical test of strata safety thickness,combined with the karst geological conditions in Guangxi,the treatment countermeasures of karst collapse are studied in depth from macro-regional prevention to engineering and technical treatment,from treatment principles to specific treatment measures. |
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