Study On The " Four Vibration-induced Effects"of Loess Under The Effect Of Locomotive Vibration——Promoting Cracking,infiltration,disintegration And Sliding Under The Effect Of Locomotive Vibration

The combined effect of long-term locomotive vibration and rainfall infiltration can lead to the instability of the slopes around the railroads,which poses a great hidden danger to the construction and safe operation of the railroad,so the loess landslides and slacktips around the railroad under the combined effect of locomotive vibration and water has attracted the attention of the academic community.A systematically in-situ and indoor experimental study on “four vibration-induced effects”,which is "promotion of cracking,infiltration,disintegration and sliding",is carried out in this paper.The following conclusions are drawn from the study.(1)The development and expansion process of loess cracks under the combined action of locomotive vibration and water were simulated by indoor tests.The experimental study found that the number of loess cracks under the combined effect of locomotive vibration and water increased significantly,and microcracks was closured during the development of loess cracks.The micro-mechanical mechanism of locomotive vibration promoting cracking can be proposed based on the soil mechanics for unsaturated soils.On the one hand,locomotive vibration accelerates the discharge of pore air,on the other hand it promotes the mutual slip of loess particles,causing the rearrangement of loess particles in a short time,which is manifested in macroscopic as a series of micro-cracks at the weak point of loess body developed.With the acceleration of water infiltration,the rapid increase of porewater pressure makes up for the rapid decrease of pore air pressure,and closuring part of the original microcracks.With the joint action of locomotive vibration and water,the matrix suction,surface tension and infiltration repulsion further cause the increase of horizontal tensile stress,promoting the formation and expansion of cracks.(2)Locomotive vibration breaks the boundary effect of disintegration of original loess and promotes the development and expansion of internal weak structural surface of loess samples,which accelerates and deepeneds the disintegration of loess.Based on the indoor disintegration test,it was found that the disintegration rates and the growth rates of loess samples under locomotive vibration were significantly higher than those under non-vibration,and the response of loess samples with lower initial water content and smaller sample size to locomotive vibration during disintegration was more obvious.The evolutionary process of the locomotive vibration-promoted disintegration effect is divided into two main stages.In the first stage,the locomotive vibration causes a large amount of air discharge inside the loess,and the expansion force of the air bubbles causes the saturated loess particles on the surface of the loess to be separated,and the locomotive vibration also causes a series of surface and internal microcracks in the weak areas of the loess sample developed.At the second stage,the microcracks further expand and penetrate under the joint action of locomotive vibration and water,resulting in disintegration of the loess sample into multiple loess blocks,the increasing of the surface area of loess led to the air bubbles further escape,which further leads to the weakening of the cementation force between soil particles,and then it promots the development of the disintegration process of loess.(3)Loess infiltration tests based on indoor and outdoor show that under rainfall conditions,the locomotive vibration accelerates the water infiltration along the formed cracks.Thus,water infiltration occurs at a rate that is several or even a dozen times that of the normal rate,prompting the surface soil to quickly reach saturation and greatly shortening the saturation time.The effect of locomotive vibration on the water cycle of loess slope is that locomotive vibration accelerates the infiltration of loess slope,and then the water-fall holes and cracks are developed and expanded,finally it affects the change of slope seepage and stress field.(4)Locomotive vibration and water change the loess pore structure,promote the development and expansion of loess microfractures and connected pores,locomotive vibration promotes the saturation process of loess,resulting in the strengthening of local loess disintegration,in the process of continuous development and penetration of microcracks,the formation of potential sliding surface at the weak structural surface within the slope,and then induce loess landslide.In the process of the combined effect of locomotive vibration and water on loess slope,the vibration-induced promotion effect of infiltration and cracking are throughout the landslide development process,the vibrationinduced promotion effect of disintegration is mainly concentrated in the saturated area of loess,the vibration-induced promotion effect of sliding is the amplification and superposition of the vibration-induced promotion effect of infiltration,cracking and disintegration.