Analysis Of Stress And Failure Of Surface Layer Of Subgrade During Heavy Freight Passage

The heavy haul freight transportation has got great development in recent years. Generally axle load on present heavy line is25t, but27t and30t axle load have been running. The failure of heavy haul line during train passage is closely related to the stress state of subgrade surface. In order to study the stress path in soil element of subgrade under moving train load, in this paper, a dynamic freight-railway model is used to analyze the stress state of subgrade surface during freight train passage and influence of thickness of ballast layer, axle load, speed, and modulus of subgrade surface, track roughness on stress state and service life of subgrade surface have been investigated. It is found that:(1)Results indicate that the stress state changes from initial state to pure shear to triaxial shear and back to pure shear and the principle stress axes rotate1800though it is more complex due to the interaction of wheels.(2)Comparing effects of different factors on stress state,it is shown that:As velocity is higher than120km/h, axle load exceeds30t, thickness of ballast under0.3m, the stress path will surpass the Mohr-coulomb failure line. Which means that subgrade is not safe.(3)Track roughness has some influence on stress state of subgrade surface. Distribution of vertical stress will become more discrete with the deterioration of track irregularity, which can also increase the probability of higher stress. All of these cases tend to decrease subgrade service life. It is shown that:as25t axle load heavy haul drive at speed of80km/h, subgrade service life of FRA5and FRA4deceased respectively by33.78%and99.11%compared with case of FRA6.(4)Axle load has greater influence on subgrade service life. It is shown that:As velocity is80km/h, service life of subgrade surface dropped by50.31%,70.2%,61.02%,56.67%for case of without track roughness、FRA4、FRA5、FRA6when axle load increase from25t to30t.(5)Velocity has some influence on subgrade service life. It is shown that:as axle load is25t, service life of subgrade surface dropped respectively by42.4%,62.73%,67.04%,75.67%for case of without track roughness、FRA4、FRA5、FRA6when velocity rise from60km/h to80km/h. While service life of subgrade surface dropped respectively by29.71%,33.69%,44.9%,50%for case of without track roughness、FRA4、FRA5、FRA6when velocity rise from80km/h to100km/h.