The coupling effect of accumulated damage and impact load substantially affects the integrity of the surrounding rock structure in deep coal mining engineering, which has inhibited safe and effective coal mining. Therefore, dynamic compression tests were performed on coal measures sandstone specimens with accumulated damage using the SHPB device. The effects of a high strain rate and accumulated damage on the sandstone’s mechanical behavior and damage evolution were investigated. The results reveal that accumulated damage has a considerable impact on specimen stress–strain curves and lowers dynamic compressive strength and deformation modulus substantially. The sandstone failure mode looks to be shear failure from a macroscopic perspective, while it appears to be intergranular fracture between the mineral particles from a microscopic perspective. The macroscopic and microscopic failure mechanisms of the sandstone specimens likewise conformed to the energy absorption law. The accumulated damage factor and the accumulated damage correction coefficient were presented in order to construct a statistical damage constitutive model of rocks based on the Weibull distribution. This model provides a decent description of the effects of accumulated damage and the strain rate on sandstone’s mechanical behavior, with parameters that are all of evident physical significance.

Coal-bearing rocks are inevitably exposed to high temperatures and impacts (rapid dynamic load action) during deep-earth resource extraction, necessitating the study of their mechanical properties under such conditions. This paper reports on dynamic compression tests conducted on coal-bearing mudstone specimens at real-time temperatures (the temperature of the rock remains constant throughout the impact process) ranging from 25 °C to 400 °C using a temperature Hopkinson (T-SHPB) test apparatus developed in-house. The objective is to analyze the relationship between mechanical properties and the fractal dimension of fractured fragments and to explore the mechanical response of coal-bearing mudstone specimens to the combined effects of temperature and impact using macroscopic fracture characteristics. The study found that the peak stress and dynamic elastic modulus initially increased and then decreased with increasing temperature, increasing in the 25–150 °C range and monotonically decreasing in the 150–400 °C range. Based on the distribution coefficients and fractal dimensions of the fractured fragments, it was found that the degree of damage of coal-bearing mudstone shows a trend of an initial decrease and then an increase with increasing temperature. In the temperature range of 25–150 °C, the expansion of clay minerals within the mudstone filled the voids between the skeletal particles, resulting in densification and decreased damage. In the temperature range of 150–400 °C, thermal stresses increased the internal fractures and reduced the overall strength of the mudstone, resulting in increased damage. Negative correlations between fractal dimensions, the modulus of elasticity, and peak stress could be used to predict rock properties in engineering.

In this study, a split Hopkinson pressure bar (SHPB) test system with real-time temperature control was developed, and dynamic tests on limestone taken from deep coal mines within real-time temperatures of 25 to 800 °C were carried out. Additionally, the scanning electron microscope (SEM), X-ray diffraction (XRD), and energy dispersion spectrum (EDS) tests were conducted to analyze the fracture mechanism of limestone at real-time temperatures. The results reveal that the dynamic compressive strength of limestone linearly declines with increasing temperatures; due to not being affected by thermal shock damage, its strength degradation is not significant after cooling to room temperature, whereas the dynamic elastic modulus exhibits a negative exponential nonlinear decrease with the increase in temperatures. The average strain rate has a positive correlation with the dynamic compressive strength of limestone, while the dynamic elastic modulus exhibits variations in accordance with the Boltzmann function and its relationship with the strain rate. The combined influence of strain rate and temperature on the dynamic compressive strength of limestone can be accurately described by a binary quadratic function. The mechanism of real-time action on limestone can be divided into three stages: when the temperature is between 25 and 200 °C, crystal micro-expansion leads to the densification of micropores, which leads to the increase in limestone strength. When the temperature is between 200 °C and 600 °C, the formation of microcracks induced by thermal stress and intergranular expansion results in a reduction in limestone strength. When the temperature is between 600 and 800 °C, in addition to the continued expansion of the intergranular resulting in the increase in the number of micro-cracks, the decomposition of dolomite at high temperatures leads to chemical deterioration and further reduction in the strength of limestone.