Static and dynamic mechanical properties and macro-micro coalburst prevention mechanisms of water-immersed coal

Hydration weakens the macro-mesoscopic mechanical properties of burst-prone coal, enhances the stress wave energy reflection-refraction capability of the coal, and reduces the risk of impact energy release in water-injected roadways. To investigate the energy evolution mechanism of burst-prone coal under hydration, uniaxial compression and impact loading tests at different moisture contents were conducted. Based on energy principles, the static and dynamic energy evolution laws of burst-prone coal with varying moisture contents were analyzed. Scanning electron microscopy (SEM) and X-ray diffraction (XRD) were used to detect the fractal characteristics of roughness and elemental composition on the impact fracture surfaces of burst-prone coal, revealing the influence of moisture content on the roughness of mesoscopic impact fracture surfaces and mineral element content. The mechanism of water-induced crack propagation and coalburst prevention in burst-prone coal under impact stress waves was discussed. Results show: ① From dry to saturated states, the number and tortuosity of failure cracks in burst-prone coal under static-dynamic compression increase, with reduced brittleness and significantly enhanced ductility and plasticity. Strong burst-prone coal exhibits more intense failure and fewer cracks compared to weak burst-prone coal. ② Increasing moisture content weakens the elastic strain energy accumulation capacity of burst-prone coal under static and dynamic loading, reducing the total released energy. Under impact loading, the reflected energy ratio of weak burst-prone coal increases from 55% to 70%, and the transmitted energy ratio decreases from 9% to 3%; for strong burst-prone coal, the reflected energy ratio increases from 24% to 50%, and the transmitted energy ratio decreases from 40% to 10%. ③ Enhanced hydration causes the roughness and fractal dimension of fracture surfaces in burst-prone coal to decrease, weakening the energy consumption of local mesoscopic crack generation. Consequently, at the same impact kinetic energy, the number of impact cracks in burst-prone coal increases, creating more reflection and refraction paths for stress waves in micro-cracks. Impact energy rapidly attenuates through reflection-refraction, ultimately reducing the risk of impact energy release.