Disturbance damage mechanism of fissured rock under true triaxial shearing with different amplitude

Time-delay failure of surrounding rock is a common phenomenon in underground tunnel engineering, often triggered by the progressive failure of damaged rock under remote micro-dynamic cyclic loading during excavation. However, the influence of true three-dimensional stress states and micro-dynamic cyclic loading parameters, particularly the amplitude of loading waves, on the shear failure behavior of rock remains unclear. To address this, true triaxial micro-dynamic tests with varying amplitudes were conducted using a self-developed true triaxial shear apparatus. This study systematically analyzed the dynamic shear deformation, load-bearing capacity, energy dissipation, and damage evolution characteristics. Based on this, we propose a fractional-order energy-damage model that couples the damage growth rate with the amplitude, the shear stress level, and the input / dissipation strain energy. Furthermore, the precursors to failure were identified based on acoustic emission (AE) monitoring. Experimental results and AE analysis revealed that as the amplitude increases, the strain rate intensifies, shifting from a broad U-shaped curve to a more distinct V-shaped trend. Concurrently, the strain energy per unit time and the proportion of energy dissipated through micro-dynamic processes relative to total energy also increase. During the cyclic loading phase, AE signal frequency rises, and the oscillation amplitude of the b -value significantly enlarges. At the point of failure, the proportion of shear cracks dramatically escalates. These findings provide critical insights for predicting the long-term stability of granite surrounding rock under dynamic loads. • With increasing amplitude ( A ), the strain rate increases gradually from U-shaped to V-shaped. • As the A increases, the strain energy accumulated in the granite per unit time also rises. • As the A increases, the proportion of energy dissipated gradually increases. • A damage model that varies with A was developed and fitting well with test results. • With the increase of A , oscillation amplitude of b -value increases significantly.