The aim of this paper is to determine the influence of heating rate on the dynamic mechanical performance of coal measure rocks after heat treatment. Uniaxial compression tests were conducted using a split Hopkinson pressure bar system on coal measure rocks after heat treatment at 800°C at different heating rates. The results reveal that a high-temperature treatment changed the physical and mechanical properties of the sandstone. When the heating rate was increased, the natural and mechanical properties were reduced gradually. The failure mode of sandstone after heat treatment was tension destruction, and shear fracturing occurred locally only at high heating rates. Original cracks grew inside the sandstone after heat treatment, while the number of defects (including cracks and pores) increased gradually with an increased heating rate, which was the main reason for the change in the sandstone’s macromechanical properties. The energy dissipation during fracturing was correlated closely to the fracture characteristics and increased with increased heating rates. The results of this work can provide references for future engineering projects, such as underground coal gasification and coal-bed methane thermal exploitation.

Investigation of the damage characteristics of rock material under the combined effect of cyclic load and impact load is extremely crucial for many mining engineering applications. Based on energy dissipation theory, we considered factors such as circulation times, the cyclic stress of a uniaxial cyclic load test, and the impact pressure (strain rate) of a split Hopkinson pressure bar (SHPB) test, studying the damage mechanism of red sandstone under the combined action of a uniaxial cyclic and impact loads. We found that when the load stress is 60%, 70%, and 80% of the uniaxial compressive strength (UCS) of red sandstone, the stress can still promote the development of microcracks and the generation of new cracks in the rock, increasing the inner damage of the rock so that it reduces the rock strength. As the cyclic time increases, the energy dissipation ratio presented a trend of decreasing dramatically and then maintaining basically no change, and the peak strain and the damage variable of the rock both increased first and then tended to remain relatively constant. The damage variable of the rock specimen under the combined action of the uniaxial cyclic loading and impact load had a significant corresponding relationship with the initial damage. As the rock specimen initial damage increases, the damage variable and the peak stress of the rock specimen both decreases almost linearly with initial damage. Meanwhile, the average particle diameter of the rock specimen after breakage gradually increased, showing a positively correlated tendency. The ratio between the fragment quality of the bigger particle diameter in the total rock specimen quality gradually increased. Under the conditions of the same initial damage, a higher impact pressure resulted in smaller rock fragment average particle diameters.

The seepage action of underground water accelerates the deformation of roadway surrounding rock in deep mines. Therefore, the study of creep characteristics of surrounding rock under seepage action is the basis for the stability control of roadway surrounding rock in deep water-rich areas. In this paper, a seepage-creep coupling test system for complete rock samples was established. Combined with a scanning electron microscopy (SEM) test system, the seepage-creep law of coal measures sandstone and the damage mechanism were revealed. The study results showed that the maximum creep deformation of sandstone under natural and saturation state decreased gradually with the increase of confining pressure, and the maximum creep deformation under saturation state was greater than the corresponding value under natural state when the confining pressure was same. When the confining pressure was constant, the creep deformation, the constant creep deformation rate and the accelerated creep deformation rate of sandstone increased rapidly with the increase of infiltration pressure. With the change of time, the change of permeability parameters went through three cycles; each cycle was divided into two stages, slow change stage and rapid change stage, and the rate of variation increased with the increase of the seepage pressure. Based on the macroscopic and microscopic characteristics of sandstone rupture, the connection between macroscopic and microscopic mechanism on sandstone rupture was established. The results in this paper can provide a theoretical basis for stability control of roadway surrounding rock in water-rich areas.