Stress And Deformation Analysis Of Pile Anchor Support Foundation Pit Under Overload

In recent years,in the highly modern urban construction,the environment is becoming more and more complex,and the foundation pit engineering near the existing buildings and underground pipelines is more and more,and the deformation control is more and more strict.Because of the improper consideration and unreasonable design of the existing buildings around the foundation pit,the collapse accidents of the foundation pit are common.Therefore,it is very important to study the stress and deformation of the foundation pits of adjacent buildings,especially those of adjacent shallow foundations.In this paper,relying on a supporting public pile-anchor supporting foundation pit project in Gaobeidian Village,Beijing,considering the overload of shallow foundation buildings at 5 meters east of the foundation pit,the following aspects are mainly carried out:using FLAC^3D software,which is widely used in foundation pit engineering,a three-dimensional numerical analysis model is established,the law of stress and deformation of the supporting structure and surrounding surface of foundation pit are analyzed;The influence range of hidden Corner effect are analyzed and the optimum design of supporting structure in this range are put forward,and a new calculation method of spacing between supporting piles is proposed based on the unified strength theory.The main research results of this paper are as follows:（1）With the increase of excavation depth of foundation pit,the horizontal displacement,bending moment of pile body and anchor cable axial force gradually increase;the maximum position of horizontal displacement of pile body gradually moves downward from the top of pile;the bending moment curve of pile body is"bow"shape,the position of maximum positive and negative bending moment is downward,and the maximum positive bending moment is less than the absolute value of maximum negative bending moment;the axial force of anchor cable is the largest and basically unchanged in the free section,it decreases rapidly in the anchorage section.Under overload condition,the horizontal displacement,bending moment of pile body and anchor cable axial force are much larger than those without overload.（2）With the increase of pile diameter and modulus of elasticity,the horizontal displacement of pile body decreases rapidly,and the maximum position of horizontal displacement gradually shifts from the upper part to the top;the bending moment of pile body increases gradually,the position of maximum positive bending moment remains unchanged,the position of maximum negative bending moment decreases,and the bending moment of pile body changes from two zero points to one zero point.When the insertion ratio of supporting piles increases from 0.2 to 0.4,the horizontal displacement and bending moment of the pile body decrease obviously.After that,the insertion ratio of supporting piles continues to increase,and the horizontal displacement and bending moment of the pile body hardly change.Whether there is overload on the top of the pit or not,the changes law of horizontal displacement and bending moment of the pile body are the same,and the numerical values are quite different.（3）Overload condition,surface additional settlement of foundation pit distributes in a"groove"shape,which is larger in the range of 2-fold excavation depth and almost zero outside.The change of excavation depth and insertion ratio of supporting piles has little effect on the surface additional settlement,while the diameter and elastic modulus of supporting piles have great influence on the surface additional settlement.（4）Whether there is overload or not,the horizontal displacement of crown and waist beam,the axial force of anchor cables and the additional settlement of ground surface in a certain range are reduced to varying degrees by the hidden corner effect.Therefore,the supporting structure can be optimized by using the hidden corner effect to save the cost.（5）Lead into the unified strength theory,a new method for calculating the spacing of supporting piles is proposed.This method can take into account the influence of intermediate principal stress,which is more reasonable than the traditional Mohr Coulomb strength theory.