Study On Laboratory Test Of Track Slab Model Impacted By Ice-block Detached From High-speed Train

When a high-speed train runs in winter snowy weather,negative pressure is formed around the car body,and the surrounding rain and snow move toward the surface of the car body.The bottom of the train,especially the bogie area,is eazy to accumulate snow and ice.With the vibration of the train and the increase of the ambient temperature,the ice-blocks attached to the bottom of the train will detach and impact on the concrete track slab.Due to the high speed and large mass of falling ice(equivalent to the speed of the vehicle),it may cause damage such as micro-cracks in the track slab.The accumulation of these damages will reduce the long-term service performance and service life of the track.Coupled with the structural characteristics of "difficult to repair and low maintainability" of ballastless track and its extensive use,it may bring service safety problems to high-speed railways.At present,there is no in-depth organization and implementation of relevant basic theoretical and technical research on the impact damage to the track slab caused by falling ice.Therefore,it is of great theoretical and engineering application value to study the impact and damage effects of detached ice-blocks falling off high-speed trains on concrete track slabs.Due to the strong randomness and uncertainty of ice-blocks falling off high-speed trains,it is difficult to determine the position,mass and speed of ice-blocks falling off.At the same time,the impact test on the track may be destructive.Therefore,this thesis intends to use laboratory model impact test to carry out basic research,analyzing the impact of ice-blocks on the track slab model.The main research work includes: Proposing an laboratory model test method for the impact of ice-blocks falling off high-speed trains on track slabs,using gas gun to drive ice-blocks to impact track slab models,establishing an impact dynamic response measurement system and a damage measurement system.The impact dynamic response measurement system includes strain,acceleration and impact force measurement systems;The damage measurement system includes three-dimensional topography,hardness and ultrasonic wave velocity measurement systems.Based on the established measurement system,model tests were carried out,the strain and acceleration response characteristics of the track slab model were obtained,the time history of ice impact force was measured,and the topography,hardness and model wave velocity changes of the track slab model after the impact were mastered.Research indicates:(1)Both the strain and acceleration response amplitudes of the track slab model increase with the increase of the ice impact velocity.When the impact velocity is 58.6～106.2 m/s,the tensile strain amplitude on the side of the model increases from +271 με to +871 με,the compressive strain amplitude increases from-190 με to-899 με,and the center acceleration amplitude on the back of the model increases from 30421 g to 64397 g.(2)The magnitude of the impact force of the ice-blocks increases with the increase of the speed.When the impact speed is 48.0～131.4 m/s,the magnitude of the impact force increases from 20.24 k N to 107.56 k N.There is also an obvious linear relationship between the impact force amplitude and the kinetic energy of the ice-blocks.(3)When the ice impact velocity is 58.6～106.2 m/s,the damage of the impact surface of the track slab model can be divided into three levels: I-level damage(almost no damage):the impact surface has no obvious changes visible to the naked eye,and the topography,hardness and wave speed measurement results are almost unchanged;II-level damage(mild damage): there is visible wear in the impact area but no visible cracks,the maximum depression depth is about 0.22 mm,the maximum increase in hardness is about 15%,and the maximum reduction in wave speed is about 6%.III-level damage(obvious damage): the impact area is obviously worn,and there are micro-cracks visible around the worn area.The maximum depression depth is about 0.46 mm,the maximum increase in hardness is about25%,and the maximum decrease in wave speed is about 12%.