Finite Element Analysis For Pile-strut Bracing Structure Of Unbalanced Excavations

With the development of economy and urbanization, less and less land is available in downtown. Construction of large underground space has become a necessity. More and more deep foundation pits are constructed.As the depth and loading around the excavation are not the same, they have different stress and deformation.In this paper, we focus on the unbalance braced excavation and do the following research:Considering the overall loading of foundation pit, using Harding-soil soil constitutive model, with Pile unit for pile and Anchor unit for brace, we established two-dimensional and three-dimensional numerical model with a pile-soil contact element.In this model we activate and kill some elements to simulate the excavation step and make the results closer to the engineering practice.Firstly, we established two-dimensional numerical model under unbalanced loading. As the loading changed, we studied the variation law for stress and deformation of the supporting structure in every excavation step. The result shows that there has large difference in the moment and displacement on each side of the pit, which should be taken into account when doing pit excavation design.Secondly, to study the influence of local loading on the supporting structure, we established three-dimensional numerical model under unbalanced loading. The result shows that the affected area of local loading is not very large.Thirdly, considering different excavation depth and various boundaries, we established three-dimensional numerical model under unbalanced excavation. The result shows that the depth of excavation has a significant impact on the moment and displacement of the supporting structure.Finally, we proposed the optimum design of unbalanced braced excavation. Respectively, we took a case study of braced excavation under unbalanced loading and different deepening to compare the optimum design method in this paper and the traditional design method, and verified the optimum design method is reasonable.