Mechanisms Influencing Mine Water-Induced Damage in Coal, Including the Coal Gangue

Hazards such as water inrushes and water-induced rock bursts are major safety challenges in China's coal mines and the occurrence of these disasters is closely related to the deterioration of the mechanical properties of the strata by mine water. However, the damage mechanisms under different hydrochemical conditions remain elusive, especially the mine water-induced deterioration of coal seams in the presence of coal gangue. In this work, the characteristics and possible mechanisms of coal damage are analyzed with different mine water conditions. First, the mineral phase composition and element distribution patterns of coal gangue were characterized by XRD, XRF, and elemental mapping. Then, the ionic constituents of the coal gangue leachates were determined using ICP and IC. Finally, uniaxial compressive strength tests were performed to evaluate the effects of mine water on the mechanical behavior of the coal, followed by a mechanistic interpretation of water-coal interactions. The analyzed coal gangue was primarily composed of minerals such as quartz, albite, and kaolinite, with Al₂O₃ and SiO₂ accounting for ≈ 90% of its total composition. The coal gangue leachate exhibited weak alkalinity, with the primary released ions being Al and Si. The concentration of SO₄²⁻ gradually increased with prolonged soaking time, while the concentrations of Ca, Mg, and Fe ions were all < 10 mg/L. Immersion in mine water greatly reduces the uniaxial compressive strength and elastic modulus of the coal. Specifically, after immersion in half-concentration mine water, the strength damage of coal was 3.63 MPa, which is notably less than the ≈ 7.6 MPa damage observed after immersion in deionized water and full-concentration mine water. The study also revealed that the coal gangue modulates the intensity of water-coal interactions by altering the ionic concentration of the mine water, thereby mitigating the mine water’s erosion of internal pores and surface structures of the coal, reducing the deterioration of its uniaxial compressive strength. This study demonstrated that the damage of coal induced by mine water is influenced by the ionic concentrations of the mine water, which is influenced by the coal gangue. This work provides a new perspective on the mechanisms potentially underlying some water inrush incidents.