Model Test And Particle Flow Simulation Of Soil Arch Effect On Seismic Performance Of Shield Tunnel

China is currently undergoing large-scale urban space development and construction.The construction of urban underground structures,represented by subway tunnels,has made a rapid development.China is the country with the highest seismic risk in the world,and most of the cities are located on or near different seismic zones.The anti-seismic pressure on urban underground facilities is huge,and it is very important and urgent to carry out research on the seismic performance of urban underground structures(represented by shield tunnels).The soil arch effect affects the magnitude and direction of the earth pressure acting on the underground structure,which in turn affects the stability of the underground structure.In the current research on the seismic performance of underground structures,the effect of soil arch effect is often neglected.To address this problem,this study conducted a Trapdoor shaking table model test based on the classical Trapdoor model test,and established a shaking table model test particle flow dynamics calculation model and a shield tunnel particle flow dynamics calculation model,respectively,to study the formation and development of soil arch effect above the tunnel,the influence of seismic effect on soil arch effect,the change of permanent load above the tunnel caused by the recession of soil arch effect and the change of seismic response of shield tunnel under the influence of soil arch effect,and the influence of soil arch effect on the seismic performance of shield tunnel is discussed.The main conclusions of this study are as follows:(1)The trapdoor shaker model test are basically consistent with the particle flow simulation results.The micro-structure parameters selected and the artificial boundary set in this paper can effectively ensure the reasonableness of the particle flow simulation calculation.(2)The development stages of the soil arch effect can be divided into the initial stage,the transition stage and the stabilization stage.The influence area of soil arch effect is symmetrically distributed along the center of Trapdoor with a width of 2B(B is the width of Trapdoor).The soil pressure in the influence area is non-uniformly distributed,where the soil pressure on the Trapdoor area gradually increases from the edge to the center,and the soil pressure on the fixed area gradually decreases from the edge to the center.(3)The soil under the influence of soil arch effect can be divided into collapse zone,loosening zone and stability zone.The affected soil force chain can be divided into strong force chain zone and weak force chain zone.The soil load above the collapse zone is transferred to both sides through the strong force chain zone..(4)The main reason for the decline of soil arching effect is the damage caused by earthquake action on the strong chain area.The smaller the soil burial depth and the greater the Trapdoor displacement,the more obvious the damage caused by earthquake action on the strong chain area,and the more severe the decline of soil arching effect.Strengthening the soil in the strong chain area through grouting and other means can effectively improve the stability of soil arching effect.(5)The results of the Trapdoor shaking table model test show that the soil arching effect can effectively reduce the soil pressure on the shield tunnel before and after earthquake action,which is beneficial for the stability of the tunnel.The critical burial depth of soil is 3B(B is the Trapdoor width)and the ideal range of average height of formation loss is 1.3% B to 4.2% B.When the burial depth of soil is greater than the critical burial depth and the average height of formation loss is within the ideal range,the impact of seismic action on soil arching effect is minimal.(6)The soil arch effect will change the initial stress field of the shield tunnel,and the initial lining internal force of the tunnel will decrease with the development of the soil arch effect.(7)Under the action of earthquakes,the soil arching effect caused by the depth of soil cover and the loss of strata will only have a significant impact on the axial force increment in the tunnel lining,while the impact on the bending moment increment is relatively small.When the formation loss rate exceeds 1.2%,the increment of axial force rapidly increases with the increase of formation loss rate;When the buried depth of the soil exceeds 3 times the tunnel diameter,the axial force increment in the lining stabilizes at around 1.36 times the initial value.(8)During the construction process of shield tunneling,the formation loss rate can be controlled at around 1.2% by controlling the excavation posture and speed of the shield tunneling machine,the torque and speed of the cutterhead,the support force of the excavation surface,and the grouting rate at the shield tail.This can ensure the seismic stability of the shield tunneling while meeting the requirements of engineering economy.