Influence of hardness on the deformation and acoustic emission characteristics of rock-like models

The deformation characteristics of fractured rock masses and the acoustic emission (AE) (microseismic) characteristics of internal crack propagation are important research topics to help evaluate and predict the stability of rock masses. In this study, rock-like models of the same scale but with different degrees of hardness were prepared by changing the ratio of rock-like materials, and in each model, a fracture of the same scale was prefabricated at the same position. Uniaxial compressive deformation and AE tests were conducted on these rock-like models. Based on the stress–strain relationship during the compressive deformation of the models, the compressive deformation process could be divided into four stages: stage I is the medium compaction stage; stage II is the elastic deformation stage; stage III is the crack propagation stage; stage IV is the model failure stage. The deformation test results showed that the variation trends in the maximum principal strain with time at measuring points on both sides of the prefabricated fractures were the same. The maximum principal strain peaks at these measuring points showed an opposite variation trend with the model hardness. The deflection angle range of the local principal strain at the passive loading end increased with the increase in the degree of hardness, while that at the active loading end did not change significantly. The relative displacement rate changed significantly mainly in the medium compaction stage; the harder the rock-like model, the lower the peak relative displacement rate. Based on the observation results of the AE test of the rock-like models, the ring-down count vs time curve could be divided into three stages: initial, growth and stable stages. The initial stage corresponded to deformation stages I and II. In this stage, the ring-down count of the hard rock-like model showed little variation, and the cumulative ring-down counts increased gradually. The growth stage corresponded to deformation stage III, where the ring-down count increased sharply, and the harder the rock-like model, the higher the growth rate of the cumulative ring-down counts. The stable stage corresponded to deformation stage IV, where the distribution of the ring-down count of the rock-like model with a relatively higher hardness was sparse, and the cumulative ring-down counts were either stable or increased steadily. Corresponding to the medium compaction stage (stage I) and the crack propagation stage (stage III) of the rock-like model, with the increase in the hardness of the rock-like model, the frequency bandwidth of the peak frequency distribution of the AE signals of the models tended to narrow. Corresponding to the elastic deformation stage (stage II), with the change in the hardness, the frequency bandwidth of the peak frequency distribution did not change significantly. The above test results provide an experimental basis for studying the influence of rock-like model hardness and prefabricated fractures on the deformation process of model medium and fracture development.