Study on the mechanical behavior and energy evolution mechanism of coal samples with water content under dynamic load: Field and experimental tests

In the process of coal mining, the mechanical properties of coal are very important for safety production. Especially under the coupling of water and rock, the mechanical behavior of coal becomes more complex, increasing the difficulty and danger of coal mining. This article adopts a combination of theoretical research and engineering practice to deeply study the dynamic characteristics and failure features of water bearing coal, and establishes a corresponding constitutive model based on Weibull distribution. The experimental results show that the dynamic tensile strength of dried coal samples is higher than that of the other three types of coal samples with different moisture contents. However, under high strain rate conditions, the tensile strength of saturated coal samples is greater than that of unsaturated coal samples, indicating that the strengthening effect of water on the coal body gradually offsets the degradation effect. In addition, based on the widely used Kelvin Voigt model, factors were introduced to modify the statistical damage variables, resulting in a higher fitting accuracy between the modified damage constitutive model and the experimental curve. In addition, the energy consumption relationship of water containing coal is studied, and the dissipated energy index K is defined. It was found that the dissipated energy index K of water bearing coal during uniaxial impact is remarkably consistent with its dynamic strength. The higher the strength, the greater the K value, indicating that more energy is consumed during the failure process. Finally, based on engineering practice, the antiscouring effect of coal seam water injection is tested. By comparison, it can be seen that the frequency and energy of vibration events in coal seam 68003 significantly decreased after water injection, indicating that with the increase in water injection time, the toughness of the coal body improves and the brittle characteristics of the failure process weaken.