Vibration Response Characteristics And Derailment Evaluation Of Subgrade Under Earthquake-High-Speed Railway Moving Load Coupling

The vibration response of track and roadbed under dynamic load is one of the keys to solve the safe operation of high-speed trains on track.Previous studies usually only consider the moving load of trains,but in fact,due to the wide distribution range,high frequency and large intensity of earthquake activities in our country,the probability of trains running on track is greatly increased when earthquakes occur.Therefore,a three-dimensional refined dynamic finite element model of ballastless track-subgrade-foundation interaction under three-dimensional earthquake and moving load is established,and the difference and relationship between the vibration performance of subgrade and track under moving load and earthquake-train moving composite load under different running speeds(v=50m/s,70m/s,100m/s,130m/s)are studied.On the other hand,the increase of train speed means that the critical speed effect is becoming more and more common on high-speed railways.If not solved,it may lead to train safety problems and increased maintenance costs.This paper analyzes in detail the influence of earthquake-train moving load characteristics on track dynamic behavior and subgrade as well as transient derailment criteria,and discusses the critical speed and derailment mechanism of high-speed trains under the action of large earthquakes.The derailment criteria considered include the ratio of lateral force to vertical force(derailment coefficient)and the lateral deformation of tracks,so as to seek reasonable improvement to minimize the risk of large earthquakes.The main research work and contents are as follows:(1)A three-dimensional coupling dynamic model of ballastless track-subgrade-foundation interaction is established.Spring damping and complex boundary conditions are set between rail and fastener.Viscoelastic boundary is applied on the periphery and side of the model to simulate the propagation of wave from finite field to infinite field.The moving load of the train is simulated as a series of moving wheel load units by the programmed DLOAD subroutine.The earthquake load is applied through acceleration in three directions,the seismic intensity is set to 7 degrees,and the maximum value of earthquake acceleration is converted to 0.1 g according to the reference code.(2)The accuracy of vibration displacement and vibration acceleration of the model is verified by the analytical solution of degraded Euler beam model and field measured data.The derailment coefficient D less than 1(the non-derailment standard for trains considering certain safety margin)output by the model only under the action of train moving load conforms to relevant national safety standards,and the correctness and feasibility of the model are verified laterally.(3)Under the joint action of earthquake and moving load,the amplitude of vibration displacement is mainly affected by earthquake load,and the vibration acceleration and frequency spectrum are mainly affected by train moving load.Under the combined action of load,the amplitude of vibration displacement of elastic subgrade is much smaller than that of saturated subgrade.The vibration acceleration of elastic subgrade is greater than that of saturated subgrade.The derailment coefficient and lateral deformation of elastic subgrade are smaller than those of saturated subgrade.(4)The critical velocity of the model under earthquake-moving load is 50m/s(18Okm/h).The critical speed is relatively low,and high-speed trains tend to exceed the critical speed,inducing ground waves to cause strong vibration of track structures.Under the combined load,similar derailment movement can be observed regardless of the vehicle speed.When the lateral deformation and derailment coefficient of the train seriously exceed the standard,the vehicle may lose stability and even derail,such as the running speed of 50m/s under the combined load.(5)Pile-supported subgrade can obviously reduce the amplitude of vibration displacement of rail structure,especially in X and Z directions,which can prevent train derailment or overturning to some extent.The track and bed vibration displacement of pile-supported subgrade and freestyle subgrade under the coupling action of moving load and seismic load at different speeds have similar variation trend,but pile-supported subgrade has excellent damping effect on seismic load.Pile-supported subgrade has a great influence on derailment coefficient of high-speed trains,with a maximum reduction of 42%.It has little influence on the lateral displacement of wheel and rail,generally 20%～30%.