Analysis Of The Influence Of Engineering Pile On The Foundation Pit Rebound Deformation And Research On Its Calculation Method

In the process of foundation pit excavation,the unloading effect will lead to the rebound deformation at the bottom of the foundation pit,which will have adverse effect on the superstructure,and the influence of the existence of engineering piles on the rebound deformation of the foundation pit can not be ignored.It is of great significance to explore the influence law of foundation pit pile on the rebound deformation for ensuring the safety of foundation pit construction and controlling the stability of engineering.Based on the foundation pit engineering of Taihu Tunnel,this paper adopts the method of field monitoring,laboratory test,numerical model and theoretical analysis to study the influence of engineering piles on the foundation pit rebound deformation and its calculation method during the excavation process.The main research contents and achievements of this paper are as follows:（1）The research status of foundation pit rebound deformation at home and abroad is reviewed systematically,and the research results of influencing factors,calculation methods and numerical simulation of foundation pit rebound deformation are summarized,and the existing problems and problems that need to be solved in these studies are pointed out（2）The engineering characteristics of taihu lake tunnel excavation are summarized including taihu lake tunnel excavation engineering survey,engineering geological conditions,and design and construction,this paper introduces the foundation pit monitoring scheme and arrangement of measuring points,the second warehouse of foundation pit and collection of the taihu lake tunnel deformation monitoring data,analyzed the deformation characteristics of the second warehouse in taihu lake tunnel excavation.（3）Based on the Taihu Lake Tunnel Project,indoor consolidation test,three-axis consolidation drainage shear test and three-axis consolidation loading and unloading shear test are carried out,so as to obtain the parameters of the small-strain Soil Hardening model（hereinafter referred to as HSS model）of the Soil.The reference tangent modulus E_oed^ref),the reference secant modulus(E₅₀^ref),the failure ratio（Rf）,the soil strength parameters（c′,φ′）and the reference loading and unloading modulus(E_ur^ref)of typical soil layers in the second pit of Taihu Tunnel are obtained.（4）A 1/4 numerical model of the foundation pit of the second bin of Taihu Tunnel was established based on the parameters of the HSS model.The finite element software PLAXIS 3D was used to compare and analyze the influence of different pile lengths,diamers and pile stiffness on the rebound deformation of the foundation pit,and the influence law of the bottom engineering piles on the rebound deformation of the foundation pit was summarized.（5）The rebound calculation formula of pile-soil composite foundation is proposed based on the transverse isotropic homogeneous model.Considering the effect of engineering piles,the parameter solution of the transverse isotropic constitutive model is adopted to establish the pile-soil homogeneous foundation pit model of the second bin of Taihu Tunnel,and the correction formula for the springback deformation calculation is proposed.