Studv On Design Of Pile-anchor Supporting System Considering Soil Arching Effect

With the development of science and technology,the pile-anchor supporting system has been widely used in practical engineering.The earth pressure serves as the primary parameter in the design of supporting structure,which has made great progress theoretically and experimentally.Up to now,the researchers mostly takes the single homogeneous soil layer behind the retaining wall as the research object.However,there are a few research study the calculation of earth pressure considering the soil arching effect between single-layer soil and two-layer soil between piles.On the basis of previous studies,this paper studies the calculation of active earth pressure between piles based on differential layer analysis method.The main research contents of this thesis are listed as following:Firstly,based on the existing theoretical calculation method of active earth pressure,the calculation model of the active earth pressure between piles considering soil arching effect and failure surface is established,and an improved calculation method of the active earth pressure between piles is proposed.Based on the horizontal layer analysis method,the analytical solutions for the active earth pressure,the resultant earth pressure and the position of the resultant action point between the piles are deduced.The applicability of the improved algorithm is verified by comparing the measured data with numerical simulation results.Furthermore,the effects of wall-soil friction angle,soil internal friction angle and the cohesion on the distribution of earth pressure intensity,the inclination of failure surface,the resultant earth pressure and the position of the resultant earth pressure action point are also discussed.Secondly,based on the improved algorithm of the active earth pressure between piles surrounded by single-layer soil,combined with the horizontal layer analysis method,the analytical solutions of the active earth pressure,the resultant earth pressure and the position of the resultant action point between two-layer soil and piles based on the sliding-arch-sliding mode and arch-sliding mode are deduced.At the same time,combined with the oblique soil layer differential method,the calculation expressions of active earth pressure,the resultant earth pressure and the position of the resultant action point behind piles considering the soil arching effect under two-layer soil are deduced.The applicability of the calculation method of earch pressure between two-layer soil and piles is verified.Thirdly,the finite element program Midas GTS is used to simulate and analyze the effect of pile diameter,pile spacing,pile embedded depth,as well as the anchor spacing,anchor prestressing and anchor inclination angle in foundation pit.The maximum horizontal displacement of the foundation pit is served as the criterion in the sensitivity analysis of each influencing factor,thus the influence degree of the factors are determined and sequenced.The factor that has the maximum influence is the pile spacing,subsequently the anchor spacing,anchor inclination angle,anchor prestress,pile diameter and pile embedded depth.Finally,based on the sensitivity analysis,the reasonable calculation method of the pile spacing considering soil arching effect is proposed.The applicability of this method is verified by comparing with the current method.The results show that for the cases without supporting structure between the piles,the pile spacing less than 2 times the diameter of piles is safe for the engineering design.By virtue of the numerical simulation,the supporting effect of the arch retaining wall and the straight retaining wall under the same supporting conditions is compared and analyzed.The results show that the supporting effect of the arch retaining wall is superior to that of the straight retaining wall.Subesquently the influence of the arch height on the supporting effect of the arch retaining wall is analyzed.It is concluded that the arch retaining wall with larger arch height offers better supporting effect,whereas it is limited by the construction site.For the cases with smaller arch height,the deformation of the foundation pit is controlled,however,the stress of the supporting structure is higher.Therefore,in the actual engineering design,the arch height should be determined according to the actual situation of the project.