Prediction Of Ground Settlement During Shield Tunneling Based On Soil Arching Effect

With the progress of urbanization,more and more cities choose to build underground rail transit to alleviate traffic congestion.The underground rail transit network is becoming more and more perfect,and there are more and more deep-buried shield tunnel projects.It is of great significance to reasonably evaluate the influence of soil arching on the loose earth pressure above the tunnel and to establish related calculation methods.In this paper,PFC^3D software is used to establish a three-dimensional meso-discrete element model and compare the results of the sandbox test.By changing the displacement of the movable gate to simulate the restriction of the tunnel lining on its upper soil,the soil arch development mode under different displacement ratios is obtained,and the calculation formula of the loose earth pressure under the restriction of the tunnel lining soil displacement is deduced.Comparing the three-phase relationship of soil compression and settlement,deriving the calculation formula of soil rebound in the loose zone,improving the method of calculating the surface settlement of the random medium theory formula in the construction phase,and combining the actual engineering monitoring data to compare and analyze,the following aspects are mainly carried out Research:1.Analyze the influence of factors such as the displacement ratio of the movable door under different buried depths in the indoor sandbox experiment on the shape of the soil arch and the vertical earth pressure.The PFC^3D software was used to establish a meso-level numerical analysis model to simulate the sandbox test,and analyze the relationship between the sliding surface and the vertical angle?of the movable door with different displacement ratios and the value range.The soil pressure changes in the horizontal direction of the movable gate were analyzed by three-dimensional particle flow simulation,and the soil arch form above the shield tunnel was determined.2.Consider that the existence of shield shells and segments in shield tunnels will hinder the displacement of the soil above the tunnel and affect the development of soil arches.Starting from the fact that the shear stress of the soil where the sliding surface is not fully developed is less than the shear strength,analogy The sand box test result shows the soil arch shape above the tunnel.The calculation formula of the width of the sliding soil column along the height of the loose zone under the influence of the included angle?is deduced.Based on indoor sand box test results and PFC^3D numerical simulation analysis,the"tower shape"is used to describe the shape of the loose zone when the relative buried depth of the shield tunnel is greater than 2,and the analytical solution of the loose earth pressure above the shield tunnel under two-dimensional conditions is obtained,and the improvement is given.Loose earth pressure calculation formula.The accuracy of the improved formula is verified by comparing the results of laboratory experiments and existing theories.3.Comparing the three-phase relationship of soil compression and settlement,based on the results of discrete element analysis,it is proposed that after construction disturbance,the existence of soil arch will transfer the soil pressure above the loose area to the arch foot,and the loose area will have unloading rebound and affect the formation loss..After the area of soil rebound caused by unloading in the two-dimensional plane,the theoretical calculation method of random medium is improved based on the rebound of soil unloaded in the loose zone,and the accuracy of the improved formula is verified by comparison with actual projects.4.Analyze the sensitivity of geological parameters based on the improved surface settlement formula,and obtain the influence of the changes of different stratum parameters after unloading and rebound of soil in the loose area on the surface settlement during the construction phase.