Study On The Regularity Of Surface Movement Caused By Excavation Of Cantilever Pile Foundation Pit

In the current construction process of infrastructure,subways,municipalities and other basic engineering facilities,the foundation pit project is an important infrastructure for the construction of foundation projects.The problem of excavation of foundation pits is no longer a traditional problem as long as the pit walls are stable to meet underground construction requirements.Deep foundation excavation needs to ensure the safe operation of adjacent buildings,roads,and urban underground pipelines.It is of great theoretical significance and engineering application value to carry out the research on the deformation law of surrounding soil surface caused by excavation of foundation pits.In this thesis,theoretical analysis,on-site monitoring and numerical simulation are combined to analyze the movement law of surrounding soil deformation caused by excavation of foundation pit under cantilever support conditions,and the following related research results are obtained:(1)This paper summarizes the deformation of supporting structures and ground surface settlement around foundation pit caused by excavation of foundation pits,and summarizes the various factors that affect the deformations during the entire construction process of foundation pits and the prediction of existing surface settlement deformation method.(2)Using the Pasternak model of the foundation reaction force model,a mechanical model was established above and below the excavation face of the cantilever support structure,and the deflection of the support structure was calculated to obtain the deflection curve(x).Then,parameters of support piles and parameters of soil are selected,and the influence of different parameters on the deflection curve is analyzed.The influence of each parameter on the deformation of cantilever support can be known.(3)The random medium theory was used to analyze the deformation of the ground surface outside the foundation pit caused by the excavation of the unit body.The mathematical expressions of the subsidence of the soil,the horizontal movement of the soil after excavation of the unit were obtained.Applying the obtained cantilever support structure deformation as a boundary condition,using the random medium theory to analyze the deformation of the ground motion of the foundation pit under the cantilever support conditions,and obtaining the results of considering the excavation of the foundation pit under consideration of the cantilever support constraints.The prediction formulas for subsidence,horizontal displacement,and oblique deformation at any point on the ground surface are analyzed.The influence of soil and engineering parameters on the movement of surface soil in deep foundation pits is analyzed using random medium calculation parameters.(4)Based on the deep excavation engineering example and the characteristics of the project,the design of deformation monitoring program for deep excavation was carried out.The FLAC3D numerical simulation method was used to predict the horizontal displacement of the excavation support pile and the deformation of the ground surface outside the pit.By comparing the numerical calculation,on-site monitoring and theoretical calculation results,the deformation law of the deep foundation pit supporting structure and the movement law of the surface soil are analyzed,which verifies that the calculation formula deduced in this paper is credible.The study of the dissertation not only obtained the law of movement and deformation of surface soil excavated by foundation pits,but also provided support for the control of excavation of foundation pits and the control and safety evaluation of soil deformation outside the pits.The research results have important theoretical significance and practical guidance value.