Study On Fatigue Damage Characteristics Of Expansive Soil Based On The Wave Velocity And Residual Strength Degradation

Expansive soil fatigue fracture is one of the main reasons for the decline of the soil strength,the essence of fatigue damage is a process that macro cracks formate during the process,the matric suction loads and unloads repeatedly with the fuction of dry-wet cycle,then a large number of micro cracks produced in the siol structure,and micro expanded gradually along with the increase of the load cycles. Based on this, The nonmetal acoustic detector TH204 is used to test P-wave velocity of expansive soil under the condition of constant amplitude dry-wet circulation,the way of using P-wave velocity to define damage variable of fatigue damage of the expansive soil is proposed.The law of the fatigue damage of expansive soil under the dry-wet circulation is explored,to discuss the rules of damage variable with cycles, cycle amplitude and the relationship between the shear strength.Finally,based on the wave velocity and residual cohesion to define damage variable, the nonlinear fatigue damage model is put forward to reflect the number of cycle and amplitude.The main results are as follows:(1) The damage variable of expansive soils is nonlinearly increased with the cycle number, the growth rate tends to be gentle.When the content moisture is higher, the damage variables is corresponding to be smaller.Dry wet cycle amplitude is greater, the greater the damage variable is. After the first cycle,the initial water content is increasing,the damage variable overall showed a decreasing trend,it is indicated that the variation of the matrix suction plays an important role on the initial damage of the specimen, the initial moisture content is higher, the smaller the damage degree is.during the 2nd to 6th cycles,the damage value changed with the initial water content variation is not obvious.(2)The cohesion C value of expansive soil and damage variable D value has a good logarithmic attenuation relationship.Under the same initial water content conditions,cycle amplitude is greater,the attenuation degree of the cohesion is decreased with the damage variable. Getting the fatigue strength of expansive soil attenuation function, it can provide a reference for the establishment of expansive soil fatigue damage model.(3)The results is tested by indoor routine tests and non metal sonic wave test system,nonlinear fatigue damage model established under wet and dry cycle expansion is simple and easy to use, but the model is only suitable for the amplitude,the establishment of variable amplitude model, it should be put forward to the reasonable test scheme.In this paper,based on the residual cohesion data of the expansion soil under wet and dry cycle,the two polynomial are given to reflect the residual variation of cohesion, the definition and expression of the expansion soil fatigue damage is also given under wet and dry amplitude cycle.The original definition of fatigue damage variable and the residual strength defined the fatigue damage variable is fitting.