The Failure Mechanism and Damage Evolution of Soft–Hard Interbedded Rocks Under the Influence of Cyclic Dynamic Loads and Moisture Content Based on Acoustic Emission

The failure characteristics of soft–hard interbedded rocks under combined hydro-mechanical action are significant for disaster prevention and mitigation in underground geotechnical engineering. This study carried out acoustic emission (AE) monitoring tests on the cyclic loading–unloading failure process of soft–hard interbedded rocks with different moisture contents. Based on the Kneedle algorithm, avalanche theory, and energy dissipation theory, it investigated such rocks' mechanical properties, AE statistical characteristics, failure mechanisms, and energy-damage evolution laws under cyclic dynamic loading and moisture effects. The results show that with increasing moisture content, both the peak stress and elastic modulus of the specimens decrease significantly, and the failure mode transitions from brittle to plastic failure. Under cyclic loading–unloading, the failure mode of the specimens is dominated by shear failure, and the higher the moisture content, the greater the proportion of shear cracks in the specimens. The probability density distributions of various AE parameters for specimens with different moisture contents all conform to the power-law characteristics, and the energy, amplitude, and duration distribution exponents all increase with the rise in moisture content. The total, elastic, and dissipated strain energy of the specimens with high moisture content are generally higher than those of the specimens with low moisture content at the same loading–unloading stage, but the cumulative strain energy in the final stage decreases with increasing moisture content. Damage variables based on dissipated strain energy and AE energy both show an upward trend as moisture content increases, which effectively characterizes the aggravating effect of water on the damage evolution of the specimens.