Deformation Failure Characteristics and Loading Rate Effect of Sandstone Under Uniaxial Cyclic Loading and Unloading

In this paper, uniaxial cyclic loading and unloading tests of equal amplitude loading with four loading rates were conducted on sandstone samples using the testing system of MTS 815.03. The evolution characteristics of stress–strain, peak stress and macro-failure characteristics of sandstone under uniaxial cyclic loading and unloading tests with four equal amplitude loading rates were analyzed. The average strength of sandstone under uniaxial cyclic loading and unloading is less than that under uniaxial compression. And with the increase of loading rate, the peak stress of sandstone nonlinearly increases and its strength dispersion decreases gradually. Moreover, the hysteretic loop of stress–strain curve under uniaxial cyclic loading and unloading has a continuous “migration” phenomenon. When close to failure, the lateral strain will suddenly increase and the strain recovery is small when unloading. The failure of sandstone is the single shear failure at a low loading rate and gradually transformed into splitting ejection failure with the increase of loading rate. The “expansion” phenomenon of sandstone represents that it enters the accelerated failure stage. The larger the loading rate is, the smaller the volume compression before critical points is. After post-peak, the greater the loading rate is, the intenser the volume expansion is. According to above achievements, the failure of the rock can be speculated by monitoring the lateral deformation of rock or lateral strain rate in practical engineering.