Research On Influence Of Pile Foundation Construction And Foundation Pit Excavation On Existing Highway Tunnels

The development of rail transit in China is changing with each passing day,and the interpenetrating problems of bridges and tunnels,tunnels and pipelines,tunnels and building pile foundations are also increasing.Pile foundation construction will disturb the soil around the pile,causing soil displacement and stress changes.This change will further affect the adjacent tunnels and make the pile-soil-tunnel influence each other.Excavation of the foundation pit will disturb the soil body at the bottom of the pit,causing large deformation of the adjacent tunnel,affecting the use and causing hidden safety hazards.Based on a rapid reconstruction project in Nanjing,this paper studies the impact of newly built pile foundations and foundation pits on existing highway tunnels.The specific research ideas and conclusions are as follows:(1)Based on the theoretical basis and engineering examples,based on the topographic features and geological distribution of the project,a three-dimensional numerical analysis model is established to simulate the entire construction process of the mud retaining wall cast-in-place pile,and analyze the stress and deformation of the existing tunnel.Focus on analyzing the changes in the soil settlement around the pile,the displacement and stress of the tunnel during the construction of the pile foundation.The calculation results show that:The soil around the pile has the largest settlement at the ground surface,the largest floating at the bottom of the pile,and the maximum horizontal displacement of the soil around the pile at the depth of 20 m.The tunnel appears as settlement in the buried section,and the settlement value decreases with the longitudinal direction of the tunnel;in the open section,the tunnel appears as the tunnel rises,but the rise is not obvious.The compressive stress of the buried section of the tunnel is greater than the mud wall protection stage during the pile filling stage,and the tensile stress of the open tunnel section is less than the mud wall protection stage.The maximum tensile and compressive stress of the lining is less than the standard strength of C35 concrete,which meets the requirements.(2).Based on the simulation of the construction of the bored pile foundation,the effect of the excavation of the foundation pit on the existing highway tunnel structure is further simulated,and it is superimposed on the influence caused by the construction of the cast-in-place pile.Focus on the analysis of the springback of the soil at the bottom of the foundation pit,the stress and strain of the tunnel,the stress and lateral displacement of the envelope.The calculation results show that: The rebound value of the soil at the bottom of the foundation pit due to the unloading effect increases nonlinearly with the increase of the excavation depth.The tunnel floats vertically in the excavation range of the foundation pit and is positive along the axis State distribution,the middle is large,and the two sides tend to zero;the horizontal direction moves into the pit.The lateral displacement of the steel sheet pile is parabolic in the depth direction,and the lateral displacement of the steel sheet pile near the tunnel side is smaller than that away from the tunnel side.(3).Analyze the sensitivity of the influencing factors,and consider the softening modulus of the mud,the elastic modulus of the soil,the friction angle in the soil,the internal support spacing,the depth of the embedded structure and the type of contact surface.The principle of single variable is used to analyze the sensitivity of the changes of each impact factor one by one.The research shows that: small mud modulus can improve the drilling efficiency,but the mud is too thin,the greater the displacement of the soil around the pile and the tunnel,the greater the borehole shrinkage.The path problem is more serious.The displacement of soil and tunnel is inversely proportional to the change of soil modulus,and the sensitivity to soil modulus is greater than the friction angle in soil.The smaller the support spacing,the deeper the steel sheet pile is embedded,the smaller the rebound of the soil at the bottom of the pit and the floating of the tunnel.(4)The bonding unit structure can simulate damage and destruction points,and can be supported and strengthened in the future construction to prevent cracks caused by the plastic damage of the tunnel.