The Stability Analysis Of Cavern Under The Pile Foundation Of Bridge In Karst Area

Karst distributes widely in our country. The cavern reduces the strength of rock. It endangers the stability of buildings foundation in Karst area. This paper is based on an actual engineering example-The grade separation bridge in The Southwestern belt highway of ZhengZhou, HeNan Province. Because of the influence of cavern and cranny underground, the pile foundation of the bridge could not be constructed normally. The designer had to change the project with putting the pile foundation on the cavern roof. Basing on the engineering, the paper analyzes the stability of cavern and draws some useful conclusion. It is hoped to be use for reference for other project.Firstly, this paper studies the reasons of the subsiding of cavern and predigests the interactional system between the pile and the cavern to a simple model. Based on the simple model, the paper analyzes the stability of the cavern roof with traditional calculation.Secondly, this paper simulates the interactional system between the pile and the cavern with FLAC3D. During the simulation, the paper simulates the actual situation as more uniform as possible with static load and dynamic load. Then, the paper compares the result of numerical simulation with the result of traditional calculation what has been draw before, and analyzes the stability of cavern.Lastly, with both the numerical simulation and the traditional calculation, this paper analyzes the influence factor of the stability of cavern, such as the shape of cavern, the size of pile, the load and so on. And it analyzes the impressionable factor what influence the stability of cavern by compare with other factors.The result indicates that it is feasible and reliable to putting the pile foundation on the cavern roof. The load is supported with the friction between the pile and the rock around. The pile and cavern are steady. This provides a way to solve the problem of buildings foundation in Karst area. In addition, it proved that the numerical simulation in stability analysis of cavern is feasible and reliable, and it can be spread and studied deeply.