Study On Deformation Of Pile-Brace Foundation Pit In Asymmetric Excavation

Pile-brace support structure can be applied to excavation engineering in a variety of geological conditions, especially in soft soil, where the support structure's superiority can be played fully. For the analysis of the deformation of pile-brace support structure, traditional pit design method simplifies the calculation, without considering the deformation compatibility of brace and support structure. With the development of urban construction, more and more deep excavations appear, and the excavation conditions are also various. There are two main excavation methods in current engineering:symmetric excavation and asymmetric excavation. The theory research on symmetric excavation becomes mature gradually, but there are few studies about asymmetric excavation. So based on the previous research work of others, the main works of this paper are shown as follows:Firstly, the deflection differential equation of beams on elastic foundation was introduced, considering the deformation compatibility of brace and support structure, the horizontal displacement and internal force of support structure at any point could be solved by Finite Difference Method and MATLAB. After comparing the calculation results with the measured values, the conclusions showed that the calculated results are close to the measured values. Meanwhile, the influences of many factors, such as the stiffness of support pile, the brace stiffness and brace position on the horizontal displacement of pile-brace support structure were investigated thoroughly.Then the FEM software PLAXIS was introduced to establish the finite element numerical model of pile-brace foundation pit in asymmetric excavation. By analyzing the factors that affect the deformation of support structure, the influences of brace size, the insert depth of wall and the thickness of wall on the deformation of support structure of pile-brace foundation pit in asymmetric excavation were discussed in detail. The results showed that these factors had a greater impact on the horizontal displacement of support structure on the deeper side of excavation than the other side. Besides, finite element models, considering different excavation depth differences, different excavation separatrix locations, different loads and different locaions of imposed loads in pile-brace foundation pit, have been established separately. And the change laws of ground settlement and bottom heave in asymmetric excavation were concluded. The results showed that there was a clear difference for ground settlement and bottom heave on two sides. Then, by changing the excavation depth difference, excavation separatrix location, load size and the location of loads, it is concluded that the four factors had a different impact both on the ground settlement and bottom heave of the foundation pit. So it is necessary to consider the structure parameter separately in engineering design and construction.