| China is located in the Pacific Rim and Eurasia two major seismic zones,karst geology is widely distributed,karst areas and seismic areas have a large area of overlap.Pile foundation due to its strong applicability,good effect and other advantages,has been widely used in the overlapping area for engineering construction.At the same time,due to the limited means of survey and high cost of treatment,pile foundation cannot be guaranteed all to pass through the karst cave and act on the intact rock mass,so there is some untreated karst cave under pile foundation.When the karst cave under the action of pile foundation load encounters the earthquake,the rock around the karst cave may be unstable,and the through failure surface appears,which seriously affects the performance of pile foundation and the safety of superstructure.Therefore,it is of great significance to research the dynamic stability of rock around karst cave under the action of pile foundation load and seismic load.This article adopts the method of theoretical analysis and numerical simulation,and the main research contents and results are as follows:(1)Based on the theory of complex variable function and the theory of elastic wave mechanics,the stability analysis model of karst cave under pile foundation load and seismic load was established,the problem was divided into three parts of stress response under gravity,pile foundation load and seismic load,the program was designed to solve the results,and superimposed the results to obtain the stress solution of the rock around the karst cave under the action of pile foundation load and seismic load,the Griffith strength criterion was introduced to evaluate the stability of the cave.The method and the numerical simulation method are used to carry out the synchronous analysis of the engineering case and the model test,and the comparison results verify the correctness of the method.(2)Based on the finite element analysis method,the analysis model of pile foundation-single karst cave-rock and soil layer was established,the effects of the radius of the karst cave,the thickness of the roof,the diameter of the pile foundation,the load of the pile foundation and the amplitude of the acceleration of seismic wave on the dynamic response of the rock around the karst cave were studied.The results show that the maximum compressive stress appears on both sides of the karst cave,and the maximum tensile stress appears on the top of the karst cave.The maximum position may change when the amplitude of seismic wave acceleration is larger(more than 0.4g).The increase of radius of karst cave,pile foundation diameter,pile foundation load and amplitude of seismic acceleration is not conducive to the stability of karst cave,while the increase of roof thickness is conducive to the stability of karst cave.At the same time,there exists a critical value of karst cave radius(1.5 times pile diameter)and a critical value of pile foundation load(5.5MPa).When the critical value exceeds,the changing trend of stress of rock around the karst cave changes.(3)Based on the finite element analysis method,the analysis model of pile foundationbeaded karst cave-rock and soil layer was established,the effects of the radius of the lower karst cave,the vertical distance between the lower karst cave and the distance the lower karst cave from the model center on the dynamic response of the rocks around the karst cave were studied.The results show that there is a critical value of the radius of the lower karst cave(2 times the radius of the upper karst cave).Before the critical value,with the increase of the radius of the lower karst cave,the pile-beaded cavern-rock and soil layer tends to be stable and safe,and the change trend of the stable state changes when it exceeds the critical value.As the vertical distance between karst cave and the distance the lower karst cave from the model center increases,the whole pile foundation-beaded cave-rock and soil layer is tend to instability of dangerous,but there is a critical value,after the critical value is exceeded,the pile-beaded karst cave-rock and soil layer is nearly transformed into a single karst cave system.At this time,the influence of these two factors becomes smaller. |
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