Numerical Analysis Of Excavation Of Deep Foundation Pit In Shanghai Soft Soil Area

With the rapid urbanization in china,there are a large number of infrastructures,all kinds of underground structures and high dense buildings to be constructed.The deep foundation pit is one of problems needs to be addressed for these projects.With the increasing density of urban buildings,the foundation pit projects are often nearby the existing infrastructures and buildings,so the construction of foundation pits is constrained by the strict environment.Because of material properties of the soft soil,such as high void ratio,high compressibility,low strength,the deformation of foundation has been a particular concern.Predicting foundation deformation caused by construction and the influence on surrounding environment,and summarizing the characteristics of deformation and studying the effects of related parameters on the deformation,have great significance to the design and construction of deep foundation pits in soft soil area.And because of the complexity of the foundation pits,it is hard to analyze the deformation of foundations with the traditional method of beams on elastic foundations or the 2D finite element method.So this article studied the deformation and the influences of related parameters(the soil and construction parameters)on deformation through three-dimensional finite element model and took a Shanghai soft soil foundation pit as an example.The major contents of this article are :1.Regarding several common existing soil constitutive models,this article discusses and summarizes their applicability in the numerical simulations.Based on the characteristics of the linear elastic model,M-C model and MCC model,the applicability of the three models are discussed.Combined with previous results,it proposed that the MCC model,which reflects the process of loading and unloading of soil and the stiffness dependent on the stress path,is more suitable to simulate the process of excavation.2.Establish the three-dimensional finite element model of a deep foundation pit composed of soil,retaining walls and supporting system.It gives treatment methods and suggestions about the simulations of soil,wall and supporting parts in the numerical model;it introduces the method to set the interaction between soil and wall;it proposes the method to implement the process of excavation in ABAQUS.This all provides a technique to predict the deformation of deep excavation.3.It analyzes the deformation of the homogeneous soil in soft area based on the deformation of retaining structures,the deformation of soil behind wall,uplift of the bottom soil and soil pressure.It studies the influence of the soil parameters,contact parameters between soil and walls and the coefficient of the lateral stress on deformation of excavation.Then it summarizes the sensitivity of the factors.4.Based on the example of a deep foundation pit in soft soil area of Shanghai,it simulates the process of excavation.And it then analyzes the deformation characteristics of walls,soil settlement behind wall and uplift of bottom soil under different conditions.5.The influence of construction parameters on the deformation of deep foundation pits are studied with above-mentioned three-dimensional finite element as an example.These parameters include the thickness of walls,the brace stiffness and spacing,the depth of cantilever excavation,soil strength.It analyzes the deformation mechanism for the lateral walls,surface subsidence,rebounding at the bottom under the influence of these parameters.