Study on Variation Law of Natural Vibration Frequency of Coal Under Water Erosion Condition

By establishing a self-vibration frequency test system, the resonance response method was used to test the acceleration response characteristics of raw coal specimens before and after drying. Then the influence of moisture on the natural vibration frequency of raw coal was analyzed by its spectral characteristics. The study found that: with the increase of water content, the stiffness of coal rock decreased, the mass increased, the damping ratio increased, and the natural vibration frequency decreased significantly (from 40.1 Hz to 37.7 Hz). The main vibration frequency domain of the raw coal specimen before drying was 29.9 Hz to 45.4 Hz, and the main vibration frequency domain after drying was 31.6 Hz to 49 Hz. The absolute deviation ratios of the upper and lower limits of the main vibration frequency domain and the natural vibration frequency before the drying of the original coal specimens were 20.8% and 20.4%, respectively, and the ratios after drying were 21.1% and 22.1%, respectively, which satisfied the frequency domain conditions for generating resonance effects. We should pay attention to the influence of moisture on the natural vibration frequency of the on-site coal and rock mass to ensure the effect of resonance control measures. The obtained results contribute to improve the resonance and prevention mechanisms of coal and gas outburst.