Study On Design And Construction Technology Of Deep Foundation Pit By Top-down Construction Method

As a kind of foundation pit construction method which can effectively economize the use of urban space,the Top-down construction method of foundation pit is widely used in various types of foundation pit projects,which can effectively shorten the construction period and control the adverse efifects of foundation pit construction on the surrounding environment.Taking Foshan Vanke Yuedu foundation pit project as an example,this paper introduces the Top-down construction technology and expounds its key construction techniques.Combined with the site geological environment conditions,the underground diaphragm wall is used as the retaining structure,and the reverse construction method is used to design and construct the whole foundation pit project.Using the finite element numerical simulation software PLAXIS and follow the Top-down construction sequence,the soil lateral displacement,vertical settlement and deformation characteristics of retaining structure in the construction process of foundation pit are simulated,and compared with the actual monitoring data.The mechanical laws of the Top-down construction method in each stage of foundation pit construction are deeply explored.It provides effective guidance for improving construction quality and correcting design conditions,and draws the following conclusions:The Top-down method can better meet the environmental protection requirements of complicated urban environment.However,with high technical requirements,its process is complex,involves a wide range of content and relatively difficult implementation.It requires strict design and careful construction arrangements before it can be implemented smoothly.The deep foundation pit with Top-down construction method has the same deformation law of the foundation pit of the open excavation method.Using the structural slab as the supporting system,its deformation control ability is strong and the environmental protection effect is good..Numerical simulations show that the horizontal displacement of the retaining structure,the horizontal displacement of the soil around the foundation pit and the settlement of the soil outside the pit increase with the depth of the excavation.The horizontal displacement distribution of the soil outside the pit decreases with the distance from the edge of the foundation pit.The distribution of the soil settlement outside the pit increases first and then decreases with the distance from the edge of the foundation pit.The displacement of the soil mainly occurs within the range of 2 times excavation depth.In addition to the conventional section calculation analysis,the foundation pit design and construction process should also carry out the overall analysis,paying full attention to the space effect of the foundation pit,the stress concentration of the anode corner part,the influence of the soil uplift of the pit bottom on the bearing capacity of the engineering pile,etc.Take appropriate measures.The soil deformation around the foundation pit is greatly affected by the soil quality of the foundation pit.However,the project is constructed by the reverse method.After comparison between the finite element simulation and the actual monitoring data,it is verified that the finite element simulation can guide the construction and ensure the deformation of the foundation pit.The parameters are all within the control value of the primary pit and the construction safety is high.