Study On The Mechanical Characteristics Of Common Walls Adjacent To Deep Foundation When Asynchronous Excavation

There are more and more deep foundation pit projects which are adjacent to existing underground structures, with the development of underground space structure.This kind of project not only need to consider the influence of new excavation on the surrounding buildings, underground pipelines, roads, tunnels and other buildings, also can not affect the stability and safety of adjacent existing underground structures, which improve the difficulty of construction. When taking account of cost savings, saving space and the using needs and other factors, the higher requirements of the project design that the new foundation pit and the existing foundation pit share underground continuous wall need to be developed. In this paper, take the shared continuous wall as the research object that belong to station foundation pit and the New Jiaotong Building foundation pit which are asynchronous construction, study the deformation law of horizontal displacement and the bending moment change of the shared continuous wall when foundation pits on both sides are asynchronous excavation, through the numerical simulation by the finite element software MIDAS/GTS. The main work and achievements are as follows:1. Analyse deformation mechanism of soil and surrounding protection structure deformation mechanism, it is introduced briefly that several calculation methods of surrounding protection structure deformation, the support structure type of deep foundation pit and the technological principle and advantages of top-down construction method and other content.2. The simulation results of continuous wall horizontal displacement show that horizontal displacement of shared continuous wall shows first decrease and then increase the final stability in general, with the excavation of the right foundation pit. The initial reduction of horizontal displacement shows the soil unloading and the heave of foundation pit at the right of shared continuous wall will reduce original horizontal displacement deformation of the continuous wall; the medium-term increasement of horizontal displacement shows the horizontal displacement of the right continuous wall also increased gradually with the increase of excavation depth; the deformation of right continuous wall has a greater influence on shared continuous wall than soil unloading and the heave of foundation pit. Horizontal displacement change tend to be stable after excavation, that is because the influence of three factors mentioned above on shared continuous wall reaches a balance. Above all, horizontal displacement deformation of right continuous wall has a relatively large influence on shared continuous wall deformation in the middle and late period of the foundation excavation. In order to reduce the influence on the shared continuous wall deformation, the excavation depth should be controlled everytime, which could reduce the horizontal displacement variation of the right continuous wall in the course of construction. At the same time, feedback horizontal deformation information of continuous wall in time by collecting data monitoring.3. The simulation results of continuous wall bending moment show that when the excavation depth of the right foundation pit is above the bottom of the left foundation pit, which has a relatively small influence on bending moment change of the shared continuous wall and would not change the original bending moment of the shared continuous wall basically. After the excavation to the bottom of the right foundation pit and pouring bottom plate, the maximum positive and negative bending moment of the shared continuous wall is changed dramatically. The analysis show that the major factor that influence bending moment change at the bottom of the foundation pit which is at the right side of the shared continuous wall is horizontal displacement deformation of right continuous wall. Accordingly, in order to prevent shear failure caused by excessive bending moment at the bottom of shared continuous wall, the horizontal displacement deformation should be controlled, which could reduce the shear force of the shared continuous wall through the medium plate of foundation pit.4. Simulated results which combine horizontal displacement with bending moment of the continuous wall shows that the major factor that influence horizontal displacement change of the shared continuous wall and bending moment change at the bottom of the right foundation pit is horizontal displacement change of right continuous wall. In order to ensure the safety and stability of the shared continuous wall, it should control the horizontal displacement of the right continuous wall reasonably in the process of foundation pit excavation.