Experimental study on damage identification of single structure plane dangerous rock masses based on constant micromotion

The dynamic parameters of the dangerous rock mass can represent the damage to the structural plane between the dangerous rock mass and the bedrock. For a dangerous rock mass in the field, measuring the first-order natural frequency by artificially stimulating the dangerous rock mass is difficult. Therefore, how to measure the dynamic parameters of dangerous rock mass based on constant micromotion remains an urgent issue. In this paper, the vibration of a dangerous rock mass undergoing excitation from constant micromotion is categorized as forced undamped structural vibration with a single degree of freedom. The ratio of the amplitude of the spectrum of the dangerous rock mass to the amplitude of the spectrum of the bedrock refers to the relative amplitude spectrum. The first-order natural frequency of the dangerous rock mass is determined at the frequency associated with the maximum peak point of the relative amplitude K > 1. The possibility of calculating the first-order intrinsic frequency of dangerous rock bodies under constant micromotion conditions was confirmed by modeling experiments using macroscopic crack-controlled dangerous rock mass (cantilever and shear fractured dangerous rock mass) and microscopic crack-controlled dangerous rock mass (sliding dangerous rock mass) as the study objects. The possibility of determining the first-order natural frequency of dangerous rock mass under underdamped conditions was experimentally confirmed. The damage and weakening of the structural plane of the cantilever dangerous rock mass and shear fractured dangerous rock mass were simulated by cutting the trailing edge cracks. Analysis of the experimental data revealed that the first-order natural frequency has a significant downward trend with an increasing degree of damage. Conversely, those of the structural plane of the sliding dangerous rock mass were simulated by hydrosol melting, demonstrating that with increasing degrees of damage, the first-order natural frequency did not change significantly, but the center frequency changed significantly. The experimental results show that the structural plane damage of the macroscopic crack-controlled dangerous rock mass can be recognized by the first-order natural frequency. The structural plane damage of the dangerous rock mass controlled by microscopic cracks can be identified by the center frequency change in the high-frequency range of the dangerous rock mass. Therefore, it will be more effective to determine the structural surface damage of dangerous rock mass by combining first-order natural and center frequencies in the high-frequency range.