Mechanical Properties and Nonlinear Energy Evolution of Holed Limestone Under Hydro-Mechanical Coupling

To investigate the mechanical properties and nonlinear energy evolution mechanism of holed limestone, triaxial compression tests under hydro-mechanical coupling were conducted on holed limestones with varying hole numbers. Based on nonlinear dynamics and rock micro-energy evolution theory, the chaotic characteristics of the energy evolution process were explored. The results show that under the action of hydro-mechanical coupling, the peak strength and residual strength of the holed limestone increase with the increase of confining pressure, and the maximum increase ratios are 25.17% and 89.33%, respectively. With the increase of hole numbers and pore pressure, the maximum decreases are 22.32%, 46.07% and 17.39%, 52.81%, respectively. The deformation and failure process of holed limestone can be divided into the following five stages: nonlinear oscillation, nonlinear transcritical stability weakening, nonlinear stability, period-doubling bifurcation before chaos, and the chaotic stage. When stress reaches 81% of the peak stress, the crack periodically expands in the rock, and as it reaches 83%, the crack irregularly expands in the rock. When the energy growth factor r is 3 and 3.57, the corresponding periodic crack propagation stress \({\sigma }_{pcg}\) ${\sigma }_{\mathit{pcg}}$ and chaotic initial stress \({\sigma }_{cis}\) ${\sigma }_{\mathit{cis}}$ can be considered as crack initiation stress and crack damage stress, which provides a new method for determining crack initiation stress and crack damage stress. The periodic crack propagation stress (representing crack initiation stress) and chaotic initial stress (indicating crack damage stress) of holed rocks gradually decrease with the increase in hole number and pore pressure, and gradually increase with the increase in confining pressure.