Study On Fatigue Failure Form And Life Prediction Of Shield Segment Under High-Speed Train Dynamic Load

With the increasing cases of shield tunnels located under railway tunnels,it is serious to consider the influence of dynamic load induced by high-speed train on the shield structure.On account of this,numerical simulation with dynamic calculation method is used to analyze the influence of dynamic load on segment of shield tunnels.The main study method and conclusion are as follows:(1)A refinement model of staggered assembling segments is used for the dynamic modelling of shield segement.Finite and infinite elements coupling calculation model is established for better simulation of infinite rock and soil.The MATLAB program is used to deal with infinite elements in bulk based on definition rules of infinite element,in which case the computational efficiency is improved dramatically.(2)The law of dynamic stress response to undercrossing tunnel is analyzed based on the numerical results.In consequence,the most dangerous position is determined according to the dynamic load of trains.The comparison with homogeneous ring model shows that staggered assembling segments model is proper in reproducing the stress of bolts and the effect on segments.(3)Research the attenuation law of dynamic load on stratum and get formula of stress change curve along the stratum depth according to non-linear fitting.Comparing with dynamic calculation method,the quasi-static method which has 30%to 45%safety stock is a more conservative design method.(4)Staggered assembling segments models in different depth are established to analyze stress response of segments and bolts in different working condition.The total stress of the segment is affected by the initial stress of the tunnel and the dynamic stress which both change with the increase of depth,in which case the total stress change trend is different with the proportion of both effect different.(5)Analyze stress change rule of two types of MJS reinforcement and got the conclusion that the effect of MJS reinforcement on the initial stress of simulated excavation is much greater than effect of dynamic load.(6)Based on stress level in different working conditions,the fatigue life can be got according to predictor formula of structure fatigue life and effect law of segments fatigue life in different depths is summarized.