Study On Vibration Response Of Subway Track And Surrounding Site By 2.5D Finite Element Method

Subway has played a positive role in alleviating urban traffic congestion and reducing urban environmental pollution However,with the increase of subway network density,and most of the lines pass through the underground of buildings,the environmental vibration caused by subway is becoming increasing ly prominent,which affects people's normal rest,and some buildings also have fatigue damage.At present,these problems are widely concerned by researchers.In this paper,the method of numerical simulation is used to study the response characteristics of the environmental vibration caused by subway and its related influencing factors,so as to provide certain reference for the prediction and evaluation of subway vibration problems.The details are as follows:A 2.5D finite element analysis model of soil dynamic response under moving load is established.Considering that the soil properties remain unchanged along the direction of load movement,a 2.5D finite element model that can reflect the three-dimensional response of soil,is established by introducin g the viscoelastic artificial boundary.The validity of the 2.5D finite element model is verified by analyzing the vibration response of soil under moving harmonic load and moving point load.The results show that: the calculation results of the 2.5D finit e element model established in this study are consistent with the existing analytical methods,and can show Kepler effect and Mach cone effect reflecting the influence of load movement speed,and has good applicability and accuracy.The vibration response of track and surrounding soil under high and low irregularity of metro train axle load and track harmonic is studied.The quasi-static term of axle load is simulated by moving multi axle load model to study the influence of axle speed and axle load frequency on the vibration response of track and surrounding soil;considering the harmonic irregularity,the coupling model of vehicle and continuous double track beam is used to simulate the wheel rail dynamic term,and the influence of vehicle speed,harmonic wavelength and amplitude on the vibration response of track and surrounding soil is studied.The results show that:with the increase of vehicle speed in a certain range,the wheel rail dynamic force first increases and then decreases;the increase of trai n speed and track irregularity will aggravate the dynamic response of surrounding soil;the soil has obvious attenuation effect on high frequency response,and the maximum response of the ground surface will move from the top of the track to a certain dist ance around the track.A vibration prediction model considering random track irregularity is established.The pseudo excitation method(PEM)is used to deal with the PSD of track irregularity,which is substituted into the vehicle rail coupling model to calculate the random wheel-rail force.Then,applied random wheel-rail force to the2.5D finite element model with PEM to calculate the random vibration response of the surrounding site.The influence of track spectrum grade,train speed,rail fastener dynamic parameters and adjustment layer dynamic parameters on wheel rail dynamic and surrounding environment vibration response is studied.The results show that: the displacement response of surrounding soil is mainly caused by axle load,and the speed acceleration response is mainly caused by random wheel-rail force.The reduction of fastener stiffness coefficient or insertion of elastic cushion in track structure has good vibration reduction effect,while the vibration reduction effect of increasing fastener damping coefficient or inserting damping cushion is less.