Dynamic Characteristics And Meso-damage Evolution Of Subgrade Soil Under Dry-wet Cycle

With the rapid development of China's heavy-duty high-speed railways,the maintenance of the infrastructure of railway subgrades during long-term use has attracted increasing attention.As an important structure that carries the upper load,the railway subgrade will receive a lot of attention due to the large changes in its performance under the combined action of dry and wet cycles and train loads.In this paper,the influence of dry-wet cycle-dynamic load on the deformation of subgrade soil is studied.At the same time,the resistivity method and CT are used to evaluate the performance decay law of subgrade soil.In this paper,the dynamic load test was carried out on the samples subjected to different dry and wet cycle times and cycle amplitudes,and the cumulative plastic strain,dynamic elastic modulus,dynamic stress-dynamic strain of the sample were studied,and after 10~4 cycles of post-loading The cumulative plastic strain prediction model is discussed.Before and after the dry-wet cycle-dynamic load,the resistivity test and CT scan were carried out,the change rule of the resistivity of the sample was analyzed,the CT scan data was binarized,grayscale statistics and three-dimensional reconstruction,and the pilot test was analyzed Such crack development law.The main research results of this article are as follows:(1)Under the same dry-wet cycle amplitude,the size change of the sample tends to be gentle as the dry-wet cycle number increases;under the same dry-wet cycle number,the sample size change becomes more obvious as the dry-wet cycle amplitude increases.The effect of dry-wet cycle on the volume is small.After the sample undergoes dry-wet cycle treatment,when the EMC(equilibrium moisture content)is reached,the volume increases by a maximum of 1.06%.(2)During the dry-wet cycle-dynamic load process,the deformation of the sample occurs intensively in the first 10 cycle loads,and its change is large and unrecoverable,and then slowly increases.The cumulative plastic strain of the sample rises with the increase of the cycle amplitude,and increases with the number of dry and wet cycles;the dynamic elastic modulus shows an upward trend at the beginning of vibration.After10 cycles of loading,the high dynamic stress amplitude(120kPa),The accumulative plastic strain growth rate slows down under the condition of high dry-wet cycle amplitude(EMC±5%).Under the condition of low cycle amplitude(EMC±1%),the dry-wet cycle effect improves the soil performance,and the dynamic elastic modulus shows a slow rise trend.The fitting results of cumulative plastic strain show that the attenuation curve is suitable for the deformation trend of the test specimen.(3)The resistivity of the sample shows a downward trend during the dry-wet cycle-dynamic load process.The dry-wet cycle effect has a significant attenuation on the soil resistivity,and the maximum resistivity attenuation is 43.9%.After the dynamic load,the resistivity further decreases.But the decay rate drops,compared with the dry-wet cycle,the resistivity is decayed by 33.12%after dynamic load.(4)The CT image analysis shows that the cracks of the sample proliferate and germinate in the dry-wet cycle,and extend from the surface of the soil to the inside.The dynamic load causes the micro-cracks in the sample to close and disappear,and the volume of the penetrating cracks decreases.However,the soil damage can be accelerated under high dynamic stress amplitude condition.The dry-wet cycle action causes the density of the soil to decrease,the dispersion of the gray distribution increases,and the vibration load compacts the soil to a certain extent,increasing the sample density.