Effect Of Pile Foundation Load On Adjacent Existing Shield Tunnel

In recent years,with the construction of urban infrastructure,the problem of interaction between pile foundation and tunnel has become increasingly prominent.At present,the problem of pile-tunnel interaction focuses on the impact of tunnel excavation on adjacent pile foundations.However,with the operation of the subway,a large number of pile foundations are adjacent to the tunnel construction,which affects the stability and control of the tunnel and its surrounding strata.Theoretical analysis and numerical simulation are used in this paper,the influence of pile foundation on the deformation of the tunnel segment during the construction stage and the stage of bearing the upper load is studied,and the influence of the pile foundation on the surrounding soil of the tunnel and the internal force and displacement of the segment is summarized.And discussed the method of controlling tunnel segment deformation.The details are as follows:(1)In terms of theoretical analysis,the displacement curve of the tunnel is obtained through a two-stage analysis method.Firstly,based on the traditional shear displacement method and its extension,the calculation of the additional stress in the longitudinal axis direction of the tunnel under the vertical load of the pile foundation is obtained;secondly,under the condition of the additional stress,the tunnel displacement curve is obtained by taking into account the influence of the tunnel stiffness and according to the known soil displacement.Compared with the numerical simulation results in the following chapters,it is found that this method can accurately predict the longitudinal settlement response of the tunnel under the effect of pile foundation load.(2)The influence of pile foundation construction stage on the deformation of adjacent tunnel segments is numerically simulated.The process of slurry wall protection is simulated by adding hydrostatic pressure.The displacement and internal force changes of soil mass and segments around the pile during the drilling process,underwater concrete pouring process and concrete hardening process are analyzed.The research results show that: the drilling process has a greater impact on the horizontal displacement and horizontal stress of the soil,and less impact on the tunnel segment;the process of pouring concrete is only when the pouring height is greater than the depth of the monitoring point.It has a greater influence on the deformation of tunnel segments.(3)The influence of single pile foundation on the deformation of tunnel segment under the action of load is simulated,the deformation results of soil and segment under the condition of single pile under load are analyzed,and the change rule of segment maximum displacement value under the change of pile length,pile diameter,pile tunnel spacing and other parameters is summarized.The research results show that:(1)With the increase of pile diameter,pile length and pile top load,the maximum displacement value of the segment gradually increases;(2)When the pile length / buried depth = 1 The segment deformation value is the largest;with the increase of the pile tunnel distance S,the segment deformation trend decreases exponentially;(3)With the increase of stiffness,the segment maximum settlement value becomes smaller and the minimum settlement value becomes larger.(4)Compared with a pile on one side and a pile on both sides,the overall settlement value of the segment is greater when there are piles on both sides;the horizontal displacement of the arch waist on both sides increases when there are piles on both sides,compared with the case with one side.The displacement of arch base and arch apex decreases and is basically zero.(4)The influence of pile group foundation on the deformation of tunnel segment under load is simulated,the deformation results of soil and segment under load are analyzed,and the change rule of segment maximum displacement under the change of pile group distribution and pile group spacing parameters is summarized.The results show that:(1)The pile group placement in the vertical tunnel direction is greater than the settlement effect caused by the piles in the parallel tunnel direction;(2)With the vertical tunnel direction The increase of the pile spacing in the direction of the upper and parallel tunnels decreases the maximum displacement value of the segment;(3)The effect of the pile spacing S3 parallel to the tunnel direction on the tunnel segment settlement is less than the effect of the pile spacing S2 perpendicular to the tunnel direction.(5)This paper summarizes several commonly used methods to control the deformation of tunnel segments,and makes parametric analysis on the effect of isolation pile on reducing the deformation of tunnel segments.The results show that:(1)with the increase of the length of isolation pile,the maximum displacement of segment decreases gradually,and when the length of isolation pile / pile group under load is 1.5-2,the deformation control effect of segment is the best.(2)With the increase of the distance between the isolated pile and the tunnel,the maximum displacement of the segment decreases.(3)With the increase of the number of isolated piles,the maximum displacement of segment decreases gradually.(4)It is of great significance to select the reasonable distance between the isolated piles to reduce the segment deformation.