Experimental Study on Mechanical Characteristics of Prefabricated Fractured Sandstone Samples under Uniaxial Cyclic Compression

The loading-unloading physical and mechanical characteristics of fractured coal-bearing strata are greatly affected by fracture occurrence. In order to study the physical and mechanical response characteristics of fractured rock under cyclic compression, this paper takes prefabricated fractured sandstone samples with different dip angles as the object, and uses uniaxial cyclic loading and unloading test to study the influence of crack dip angle on sample strength, failure mode and crack propagation law. The results show that with the increase of crack inclination angle, the cyclic loading and unloading peak strength and elastic modulus of the sample increase significantly, and the peak strain decreases first and then increases. During the cyclic loading process, the area of the hysteresis loop gradually decreases, the slope gradually increases, the energy con-sumed by the hysteresis loop gradually decreases, the cumulative plastic deformation increases, and the curve shape presents a “concave” type; when it is 15 ° and 30 °, the cracks at the crack tip are wing cracks. When it is 45 °, the cracks at the crack tip are secondary inclined cracks and wing cracks. When it is 60 °, 75 ° and 90 °, the cracks at the crack tip are secondary coplanar cracks and wing cracks. With the increase of fracture dip angle, the number of cycles and peak strength at failure are increasing.