is paper focuses on the mechanical behavior and damage evolution of Huashan granite subjected to cyclic loading. Four levels of confining pressure (0,15, 25, and 35 MPa) were applied during cyclic axial loading by using a Rock Test System (MTS815) along with an acoustic emission (AE) monitoring device. Experimental results indicate that the number of AE activities is higher under cyclic triaxial loading compared to that under cyclic uniaxial loading. e measured stress-strain curves of both uniaxial and triaxial tests under cyclic loading are concave-up, but the degree of concavity is mild for the latter. As the cycle number rises, elastic modulus of the granite sample under different confining pressures increases. e slope of the peak strength versus confining pressure plot for the cyclic loading is larger than that for the monotonic loading. Besides, it is found that the dissipated energy increases with the increase of cyclic stress, but it hardly increases in proportion with the confining pressure. e damage parameters defined in terms of the plastic strain can be extended for the whole cyclic loading process, and they agree well with the energy-based damage parameters.
To study the effects of the confining pressure (Cp) on the mechanical properties and damage evolution of deep rock masses under multiple impact loading, the improved split-Hopkinson pressure bar was used to perform cyclic impact on granite samples with Cp = 0, 4, 8, 12, and 16 MPa. The experimental results indicated that the total number of impacts increased with the increase in Cp. The sample with Cp = 0 MPa was destroyed with only one impact and exhibited a typical type-I stress–strain curve. The samples with Cp = 4, 8, 12, and 16 MPa exhibited typical type-II stress–strain curves. Under the same cyclic impact loading, a higher Cp yielded a lower rate of increase of the average strain rate and maximum strain, as well as a lower rate of decrease of the peak stress and elastic modulus. The peak stress and maximum strain exhibited a good negative linear correlation and positive linear correlation with the average strain rate, respectively. At Cp = 4 and 8 MPa, the cumulative damage of the sample gradually increased with the increase in the number of impacts. At Cp = 12 and 16 MPa, the compaction effect caused the cumulative damage to be negative in the first few impacts. Subsequently, the cumulative damage gradually increased owing to the impact damage-softening effect. Additionally, the sample with Cp = 0 MPa was pulverized, and the fragmentation was severe. At Cp = 4, 8, 12, and 16 MPa, the Cps inhibited the free expansion of internal cracks in the sample, and the sample exhibited a significant shear failure mode with less fragmentation.
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