Deformation Characteristics Analyses Of Deep Foundation Pits In Wuhan Metro Stations

With the rapid development of economy and infrastructure construction in China, the improvement of urban traffic conditions and construction of urban rail transport become increasingly important. The construction of urban rail transit projects will involve a lot of deep foundation pits, which are always in the areas with high population density, heavy traffics and a variety of municipal underground pipelines. As a result, the control of the foundation pit deformation during the construction is quite essential.Based on the construction of three stations, Zhongshan Park station, Jiyuqiao station and Xunlimen station foundation pits of the No.2 subway in Wuhan, the deformation law during construction of the enclosure structure, external ground settlement and basement uplift are analyzed in this dissertation, by using the finite difference software FLAC3D and field observation. Meanwhile, As for the Zhongshan Park station, the deformation and influence on the adjacent viaduct piles induced by different insertion ratios of the diaphragm wall are emphatically analyzed. As for the Jiyuqiao station, the analysis is fabout the effects of various reinforcement parameters of the soil in the foundation pit on the deformation of the foundation pit. In the analysis of the Xunlimen station, different precipitation schemes are adopted to study the effects of precipitation on the foundation pit deformation, and the meshless method is introduced into the analysis of soil seepage further. The dissertation includes the following contents:Firstly, the deformation characteristics of foundation pit when the diaphragm wall was not embedded into the bedrock are studied, in that case, the deformation is large in the middle of the wall while small in two ends, and the'kickout'phenomenon is obvious. With the increase of insertion ratio the "kickout" can be reduced, however, the influence of insertion ratio on the deformation can be ignored when the insertion ratio has reached a certain value.Secondly, the effects on the adjacent viaduct piles during excavation are explored. The excavation will cause additional bending moments and deformations on the adjacent viaduct piles, the effects on the deformation of adjacent viaduct piles are lessened dramatically with the increase of the distance between foundation pit and adjacent viaduct piles. Besides, the effects on the adjacent viaduct piles have also been discussed when jet grouting renforcement body is added between the enclosure structures and viaduct piles. The numerical results indicate that the main function of the jet grouting reinforcement body is to protect the viaduct piles when the diaphragm wall was in the process of construction, while its effects on the deformation of the viaduct piles are negligible.Thirdly, the law of ground settlement deformation outside the foundation pit is analyzed. The ground deformation outside the foundation pit is presented as a parabolic curve, the maximum ground settlement occurred in the location about the excavation depth away from the foundation pit. And the ground deformation decreases with the increase of distance from foundation pit, the influence range is about 4 to 5 times the excavation depth.Fourthly, the deformation induced by basement uplift in the foundation pit is analyzed. The excavation will make the basement unloading rebound and the lateral deformation of enclosure structures will increase the uplift further.Fifthly, the parameters of soil reinforcement in the foundation pit, such as arrangement pattern, width and depth are studied. The soil reinforcement in the foundation pit can effectively control the deformation of the pit. Both the width and depth of apron reinforcement have an effective range, when their values exceed the range, the effects of reinforcement will not be improved obviously. However, as for the width of sprout reinforcement, a reasonable width is determined by the control criterion of deformation. When the parameters of apron reinforcement are not determined, the deformation-control function of soil reinforcement is influenced by the replacement ratio of reinforcement, the deformation-control of the reinforcement becomes more obvious when the replacement ratio is getting larger.Sixthly, the influence of the precipitation on the foundation pit deformation is investigated. The precipitation has a significant influence on the foundation pit deformation, especially when the one-stage precipitation scheme is adopted. The results of numerical analysis show that in order to reduce the deformation induced by the precipitation, a multi-step precipitation scheme should be adopted.Finally, the meshless method is introduced into the seepage analysis. The application and prospects of meshless method in the analysis of foundation pit seepage is presented.