Study On Macro And Microscopic Deformation Evolution Mechanics Of Heavy-Haul Railway Subgrade Filling Under Freeze-Thaw Action

With the extension of the service period and the operation of large axle weight trains,the seasonal permafrost area heavy rail roadbed due to freezing and thawing caused by the disease has tended to normalize,resulting in the smoothness of the track is reduced,affecting the heavy rail capacity to enhance,costing a lot of maintenance costs.In this thesis,the Particle Image Velocimetry(PIV)technology is introduced to simulate seven freeze-thaw cycles of roadbed filler under the open recharge condition by indoor model test to study the freeze-swelling and thawing characteristics of roadbed filler under the effect of seven freeze-thaw cycles,taking the heavy-load railroad roadbed filler in the seasonal freezing area as the research object.Combining scanning electron microscopy and mercury pressure test,the microstructure of the specimens before and after the freeze-thaw cycle was studied qualitatively and quantitatively,and the intrinsic connection between macroscopic deformation and microstructure evolution of roadbed filler was investigated,aiming to reveal the evolution mechanism of freeze-swelling and thawing deformation of roadbed filler and provide theoretical basis and data support for the disease management of roadbed in the frozen soil area.The main work and conclusions of this thesis are as follows:(1)Based on the basic physical properties,the roadbed fill was a low liquid limit powder soil.The temperature and moisture sensors used for the test were calibrated.After calibration,the average temperature measurement error and the maximum temperature measurement error of the temperature sensor are 0.03 ℃ and 0.06 ℃,respectively.The Lagrange interpolation method was used to effectively reduce the measurement error of the moisture sensor,with an average absolute error of 0.56% and an average relative error of 0.43% compared to the drying method.(2)Under the open recharge condition,the freeze-thaw cycle test of the roadbed filler under the action of seven freeze-thaw cycles shows that the temperature,moisture content and overall deformation of the specimen show periodic changes with time and stabilize after four freeze-thaw cycles;Temperature variations significantly affect the deformation characteristics of the specimens,and moisture migration and ice-water phase change are the main sources of soil deformation.(3)The visual deformation tracing shows that during the first freezing process,compression deformation occurs inside the specimen,and during the seven freezing processes,the dividing line between expansion and compression is above the freezing front,where the strain value is the largest and the specimen as a whole shows expansion deformation.During the seven melting processes,firstly,the top of the specimen was deformed by expansion and the whole showed expansion deformation;after the 1st melting process,the top and bottom of the specimen were not deformed and the whole showed compression deformation.(4)During the seven freeze-thaw cycles,the water in the soil undergoes repeated phase changes and migration,and the pores in the soil are adjusted and changed.The force between soil bodies changes,the soil skeleton is reorganized;the pores in the soil are transformed from small pores to medium and large pores,the pore size increases significantly,the pore contour line is simpler,the soil structure is changed,and finally the expansion deformation is presented.