Experimental Study On Wave And Electric Characteristics Of Sandstone Under Uniaxial Equal Amplitude Cyclic Loading And Damage Evolution Analysis

In the real environment,during the construction and operation of rock mass engineering,in addition to the static load,the rock is more subject to the cyclic load,and the mechanical characteristics exhibited by the rock mass under the cyclic load and the static load are It is different,so it is necessary to study the mechanical properties of the rock under cyclic loading.Acoustic emission characteristic parameters and resistivity are both sensitive to the damage process of the rock,and can well describe the damage evolution law of the rock,and the two have a certain complementarity to different stages of rock damage.Therefore,this article relies on the National Natural Science Foundation of China(51609027),taking the typical sandstones in Chongqing as the research object,the macroscopic sandstone under the action of constant amplitude loading and unloading Deformation characteristics,acoustic emission characteristics and resistivity characteristics were tested and combined with damage mechanics,a damage model based on acoustic emission parameters and resistivity was constructed.The main research contents and results are as follows:(1)Through the constant amplitude cyclic loading test,the axial deformation characteristics of sandstone under different stress amplitudes,different frequencies and different saturation conditions were analyzed.It is found that the axial deformation of sandstone under the action of constant amplitude cyclic loading generally shows a threestage evolution law,and the hysteretic loop curve also shows a "sparse-dense-sparse" trend.With the increase of stress amplitude,decrease of frequency and increase of saturation,within the same cycle number,the greater the axial peak strain of sandstone,the greater the strain rate and the shorter the cycle period.(2)Through the acoustic emission test of sandstone during constant amplitude cyclic loading,the acoustic wave propagation characteristics of sandstone under different stress amplitudes,different frequencies and different saturation conditions were analyzed.It is found that the evolution of acoustic emission also has a three-stage rule: in the initial stage,the deformation is faster and the acoustic emission signal is strong;in the constant velocity stage,the deformation development is slower and the acoustic emission signal is more stable;Get more intense.And as the stress amplitude increases,the frequency decreases,and the saturation decreases,the stronger the acoustic emission signal generated in each cycle.(3)Through the resistivity test of sandstone in the process of cyclic loading with equal amplitude,the conductivity characteristics of sandstone under different stress amplitudes,different frequencies and different saturation conditions.It was found that the resistivity as a whole showed a rapid decline in the loading phase and a rapid rebound in the unloading phase.The changes in resistivity at different stress amplitudes show differences in the first few cycles;the overall change trend of resistivity at different frequencies is consistent,but the rate of change increases with decreasing frequency;and different saturation The trend of lower resistivity is very different.(4)On the basis of relevant established theories,the damage variable D? based on resistivity is derived,and combined with the existing damage variable Dc based on the cumulative ring count of acoustic emission,a comprehensive synthesis based on acoustic emission parameters and resistivity is established Damage variable D,thus constructing the cumulative damage evolution model of sandstone under the action of constant amplitude cyclic load.