Study On The Stress Analysis Of The Retaining Structure Of Long-short Pile Foundation Pit

The foundation pit enclosure structure is often used to solve the stability problem of the foundation pit.The design of pile length is generally designed to satisfy the overall stability of the foundation pit,but the bending moment of the pile under the pit bottom decreases with the increase of depth.It is unnecessary to waste the flexural bearing capacity at the bottom of the structure,which is often used in the form of a wall.In the case that the surrounding rock can reach the foundation pit,the pile rock has a certain difficulty in construction,and the effect of the equal-length pile into the rock is not very good.On the basis of satisfying the foundation pit safety,this thesis reduces the pile length of some piles in the equal-length piles,and becomes the composite envelope of long and short piles,which can achieve the effect of thinning in the depth of the bottom part of the pile.On the basis of previous studies,this thesis has done the following work.In this thesis,the failure mechanism of the overall buckling of the foundation pit is analyzed,and the plane anti-uplift stability model is simplified.The formula of length design formula and the corresponding stability factor formula are derived.In this thesis,the failure model of long and short piles is established based on the plane foundation model.The force of long pile and short pile is analyzed,and the boundary condition of the instability failure is put forward.Combined with the actual project,using the theory of short and long pile space failure,this thesis calculates the influence of short pile length change on the internal force of the pile under the condition of a long short composite pile.The feasibility of the design of composite envelope of long and short piles is determined.According to the research content,the overall stability of the foundation pit is controlled by long piles and short piles.The long pile length mainly controls the force of the pile,and the bending failure of the long pile is controlled.And in the case of long pile using larger proportion,due to the original length of pile length design generally on the basis of limit equilibrium,multiplied by the corresponding safety coefficient,resulting in shortened when part of the pile length,will not affect the overall stability of the foundation pit.Due to the obvious differences in soil quality,the body of the enclosure pile has a large force under the condition of poor soil quality.The short pile length should not be too short,and the proportion of long pile should be larger.In the case of better soil,the ratio of short pile and the length of short pile can be increased correspondingly.