Dynamic Characteristics Test And Damage Evolution Characteristics Of Soft Subgrade Covering Dry Crust

As a typical representative of the layered subgrade,the layer of soft soil subgrade with dry crust covering possesses high use value in engineering.In recent years,with the rapid development of the highway and the increase of traffic flow and load,the subgrade soils have different degrees of damage.Therefore,it is of great significance to study the dynamic characteristics and damage evolution characteristics of the layer of soft soil subgrade with dry crust covering under the vehicle load.First,the representative samples were collected,the change rule of dynamic characteristics of hard and soft soil layers were studied by the SDT-10 dynamic three axis instrument.The effects of moisture content,dry density,vibration frequency and confining pressure on the dynamic characteristics of hard and soft soil layers were analyzed.At the same time,the cumulative plastic strain characteristics of hard and soft soil layers under dynamic stress,moisture content,vibration frequency and confining pressure were studied,and the change rule of hard and soft soil layers under the long cycle effect were obtained.By means of data fitting,the critical vibration times of hard and soft soil layers were obtained and the formulas for calculating the accumulated damage of hard and soft soil layers were derived according to the linear cumulative damage theory and the cumulative plastic strain characteristics of hard and soft soil layers.In this paper,the damage characteristics of hard and soft soil layers were studied,and the influence of dynamic stress,thickness of hard shell layer and energy absorption coefficient of soft soil layer on the damage characteristics were analyzed.The results show that the dynamic stress and thickness of the hard shell layer have great influence on the damage of soft soil layer,the energy absorption coefficient of soft soil layer has a great influence on the damage of soft soil layer,and has no effect on the damage of hard shell layer.The effect of dynamic stress level on the damage characteristics of hard and soft soil layers were considered.The dynamic stress ratio range of hard and soft soil layers were obtained based on the field test results;the dynamic stress ratio range of hard and soft soil layers were determined by three axis test.The exponential parameters of dynamic stress level was constructed,the linear cumulative damage theory was modified by nonlinear method,and an improved formula for calculating the damage of hard and soft soil layers were obtained based on the existing empirical formula of nonlinear cumulative damage.The results show that the damage degree of hard and soft soil layers increases,the damage increases rapidly and the slope decreases gradually at the initial stage of loading.