Experimental Study on Progressive Damage Evolution in Rocks Subjected to Post-peak Cyclic Loading History

Abstract Because of the release of in situ rock stress, rocks surrounding deep underground excavations are mostly driven into a post-peak damage state. Thus, investigations on cyclic loading-induced damage of rocks are of paramount significance in terms of the long-term stability of rock structures. In this study, using a damage-controlled testing method, the effect of post-peak cyclic loading on the failure behavior of different rock types was comprehensively evaluated. This investigation revealed that post-peak cyclic loading imposes no significant influence on the overall failure behavior of rocks. The evolution of damage variables also indicated that the large portion of axial strain damage (Da) occurs during the first cycle at the peak strength, whereas lateral strain damage (Dl) evolved more rapidly than Da did in the post-peak regime under further loading and unloading cycles. The cumulative permanent axial strain (∑εap) evolved nonlinearly with the axial stress ratio (σi/σa−peak) in the post-peak regime, which was manifested as sparse-dense-sparse hysteretic loops. A rapid reduction in the crack damage stress ratio was observed for rocks in the initial sparse hysteretic loops, which was followed by a lower decrease rate in the subsequent dense hysteretic loops, and an almost constant value was finally reached in the last sparse hysteretic loops. Furthermore, tangent Young’s modulus (Etan) and Poisson’s ratio (υ) evolved in three main stages: One, Etan first increased and then decreased in the initial sparse hysteretic loops, while υ continuously increased, representing significant deformation in the lateral direction. Two, Etan decreased in the dense hysteretic loops, while υ increased at a higher rate for stronger rocks because of the decrease in Da accumulation. Three, the increase rate of υ declined in the second set of sparse hysteretic loops, and Etan decreased until complete failure occurred.