Research On Earth Pressure Considering Soil Arching Effects And A Computing Method On Double-row Piles

In foundation pit engineering,double-row piles are widely used due to their advantages of large lateral stiffness,good spatial coordination and small space occupied.In calculation of the double-row piles,the soil pressure distribution model considering soil arching effect is closer to the actual situation.Against on the weakness of the previous research,the soil arching effects theory of retaining wall is used and improved to research the calculation method of total earth pressure behind row piles from clayey backfill considering soil arching effects.The finite difference program is obtained by applying the improved theory to calculate the structural of double-row piles.Then,relying on the monitoring project of a foundation pit of a pumping station,compared with the calculation solution of Lizheng,the computed result of the improved method is more consistent with the measured data.This study can provide reference for rational design of double row pile structure.The main research contents and results are as follows:(1)At first,against on the single-row retaining piles,the principal stress rotation theory of retaining wall is used and improved by considering that the value of principal stress is changed after rotating.On this basis,by means of a stress analysis of soil arch element and solving the equilibrium differential equation,an analytical expression for the direct earth pressure is derived.Compared with the analytical solution of predecessors and the measured data,the computed result of the improved method is more consistent with the measured data.Then,the improved method is applied to the indirect earth pressure of the clayey soil,and the analytical expressions for indirect earth pressure and total earth pressure are derived.(2)This paper applies the improved soil pressure theory considering soil arching effects to the structural calculation of double-row piles.The double-row piles are divided into four parts along the sliding surface,The improved soil pressure theory is used to calculate the soil pressure above the sliding surface,the elastic foundation method is used to calculate the soil resistance below the sliding surface.Then,the double row pile calculation model and the flexural differential equations of each section is established.The matlab program for calculating the displacement and internal force of piles is obtained by applying the finite difference method.(3)The field monitoring data of a practical foundation pit project are sorted out and analyzed,focusing on the horizontal displacement of top pile,deep displacement of pile body,water level of foundation pit and surface settlement.Then,the displacement and internal force of piles are calculated by applying lizheng deep foundation pit software and matlab program and compared with the measured data.The results show that: The maximum displacement of top pile calculated by lizheng software is obviously larger than the measured value,which is about 67% larger.The top pile displacement calculated by matlab program is 15.5% larger than the measured value and closer to the measured value.(4)Then,the influence of excavation depth and geometric parameters of double-row pile structure(including pile spacing,row spacing,pile diameter and pile length)on the horizontal displacement and bending moment of double-row pile structure is studied.The results show that: The maximum horizontal displacement,maximum bending moment and maximum shear force increase exponentially with the increase of excavation depth;Pile diameter has a great influence on the maximum horizontal displacement of double row piles.In practical application,it is more economical to keep the back pile diameter unchanged and reduce the front pile diameter.The change of pile length has little effect on the maximum displacement.In practical application,it is more economical to keep the length of the front pile unchanged and reduce the length of the back pile.