Construction Technique Of Diaphragm Wall In Deep Foundation Pit Constructed By Top-down Method And Numerical Simulation Analysis Of Excavation Deformation

With the rapid development of science and technology, social economy and urbanization, the contradiction between urban spatial expansion and scarcity of land has become more and more prominent. Thus the scope of underground space utilizations has been extending. Under such background, it is essential to ensure the safety and stability of foundation pit construction, and to reduce the impact on the surrounding environment. While the traditional method of construction technique can’t meet these requirements, top-down construction technique arises at the historic moment. Compared with the traditional method of construction technique, top-down construction technique can overcome the problems of narrow construction site, limited resources. It also can reduce the engineering cost, shorten the construction period. What’s more, it can increase the stability of foundation pit, ensure the safety of foundation pit and protect the surrounding environment.Based on a deep foundation engineering constructed by top-down method, the construction and design for deep foundation pit constructed by top-down method is studied in this paper, including thickness of the diaphragm wall, buried depth, the calculation of earth pressure, determination of bearing capacity, stability of groove wall and a number of improvement measures and new technologies during the construction process of the diaphragm wall, which can provide theoretical basis for actual engineering application. Meanwhile, a three-dimensional model of deep foundation pit constructed by top-down method was established through the ANSYS software. Then the numerical simulation of deformation in excavation was carried out by importing the model into FLAC-3D. The selection of structural element and constitutive model and the determination of model parameters were discussed. The laws of the deformation of the diaphragm wall, surrounding soil settlement, bottom heave in the process of excavation were obtained.Through the research above, it can be concluded that:The adoption of improvement measures, including five-axis cement mixing pile instead of three-axis cement mixing pile, high pressure rotary jet grouting pile, sand and gravel bag instead of joint box and grooving sequence adjustment, can effectively solve the stability problem of the groove wall in the construction process and ensure the quality of diaphragm wall, so it can provide guidance for the construction of diaphragm wall in this kind of deep foundation pit. The deformation of diaphragm wall is assumed as a S-shaped curve. The maximum horizontal deformation is located at the 1/3～1/2 depth above the excavation face. Surrounding soil settlement is assumed as an inverted bow and the maximum settlement is located at 6-8m distant from foundation pit. The pit bottom rebound gradually increased with the soil excavation. The vertical displacement of pile top shows a decreasing trend and then an increasing trend with the proceeding excavation. It has important guiding significance to actual construction.