In order to study the fractal characteristics of the pomegranate biotite schist under the effect of blasting loads, a one-dimensional SHPB impact test was carried out to test the dynamic compressive strength, damage morphology, fracture energy dissipation density, and other parameters of the rocks under different strain rates; besides, sieve tests were conducted to count the mass fractal characteristics of the crushed masses under different strain rates to calculate the fractal dimension of the crushed rock . Finally, the relationships between fractal dimension and dynamic compressive strength, crushing characteristics, and energy dissipation characteristics were analysed. The results show that under different impact loads, the strain rate effect of the rock is significant and the dynamic compressive strength increases with the increasing strain rate, and they show a multiplicative power relationship. The higher the strain rate of the rock, the deeper the fragmentation and the higher the fractal dimension, and the fractal dimension and rock crushing energy density are multiplied by a power relationship. By performing the comparative analysis of the pomegranate biotite schist, a reasonable strain rate range of 78.75 s^-1~82.51 s^-1 and a reasonable crushing energy consumption density range of 0.78 J·cm^-3~0.92 J·cm^-3 were determined. This research provides a great reference for the analysis of dynamic crushing mechanism, crushing block size distribution, and crushing energy consumption of the roadway surrounding rock.

In order to effectively reduce the disturbance of the precrack blasting vibration on slope rock mass, except paying attention to the damping effect of the precrack, it is also necessary to optimize the blasting parameters and initiation mode of the precrack itself. Based on the blasting theory and empirical formula, the parameters of presplitting blasting such as the hole diameter, hole spacing, charge decoupling coefficient, and line charge density were determined, and field tests of conventional pre-splitting blasting and presplitting blasting with precise delay and hole-by-hole initiation were carried out on the west slope of Buzhaoba. Regression analysis was carried out on the vibration monitoring data, and the blasting vibration attenuation regularity of slope particles was obtained. By comparing the monitored vibration velocity of the two presplitting blasting tests and the forecast results of theoretical calculation, the average reduction rate of the conventional same row blasting vibration is 26.40%, while that of the hole-by-hole blasting vibration can reach 41.45% with a half hole rate of 80.7% and an irregularity of about 130 mm. Results show that the effect of precise delay initiation between preholes based on the digital electronic detonator is better than that of the simultaneous initiation of preholes. Therefore, it is suggested that the hole-by-hole presplitting blasting technology should be applied in the excavation of boundary slope and the treatment of high and steep slope.

Temperature’s influence on the physical and mechanical properties of rocks is a crucial concern for the rational design of deep rock engineering structures and the assurance of their long-term stability. To systematically comprehend the impact of the evolution of mineral composition and micro characteristics on the physical and mechanical behavior of thermally damaged granite, we observed the microscopic structural defects inside the rocks with a polarizing microscope and revealed the thermal damage mechanism of granite from a microscopic perspective by combining ultrasound detection and XRD phase characteristic analysis. The results show that the physical properties of the specimens changed significantly at three characteristic temperature points: 400 °C, 800 °C, and 1000 °C. Under high temperature conditions, the diffraction intensity of all minerals in granite, except for quartz, generally decreased, and stable minerals decomposed. Albite and potash feldspar decomposed to form anorthoclase, thereby reducing the structural stability of the rock material. In addition, the peak width of various minerals decreased to varying degrees with increasing temperature. The increase in mineral volume further damaged the internal structure of the rock material while promoting the transformation from grain boundary to intergranular cracks and from intragranular cracks to transgranular cracks, ultimately forming a interconnected crack network. Thermal damage significantly reduced the longitudinal wave velocity, uniaxial compressive strength, and elastic modulus of the specimens, while the stress–strain curve relationship indicated that the specimens underwent two opposite processes of transformation from brittleness to ductility and then from ductility to brittleness. The thermal damage threshold of granite in this study was 600 °C.

In this study, the dynamic mechanical properties of red sandstone at low temperatures were studied by performing SHPB dynamic impact tests. According to damage and energy theories, the influences of different low temperatures on the dynamic strength, damage variable, and energy dissipation of red sandstone were analyzed. Combined with a fracture morphology analysis, the deterioration mechanism of the dynamic mechanical strength of red sandstone was deduced at lower negative temperatures. The research results showed that lower negative temperatures (<−30 °C) caused “frostbite” in red sandstone, which resulted in a sharp reduction in the macroscopic, dynamic mechanical strength of rock under high strain. Transient engineering disasters can easily occur under such a dynamic disturbance. According to the fracture morphology analysis, low temperatures generated a large number of cracks at the interface between the components of red sandstone. The plastic deformation ability of the crack tip was poor, and stability loss and expansion under high strain rate were readily achieved, resulting in low-stress brittle failure. However, due to the complex mineral composition of the cementitious materials, they were more susceptible to low temperature. Therefore, under the double action of dynamic load and low temperatures, it was found that damage occurred in the cementitious materials first, and then fracture of the red sandstone as a whole resulted.

To study the dynamic damage and fracture of metamorphic limestone under explosive load and the stability of the surrounding rock, the stress-strain curve, fracture morphology, and energy dissipation characteristics of metamorphic limestone in the Dahongshan mining area under different strain rates were studied by the Hopkinson pressure bar (SHPB), stress wave analysis, and fractal theory. The experimental results show that the crushing form and degree are significantly affected by the loading strain rate. There are several typical failure modes. When the strain rate is 17.56 s⁻¹, there is no obvious failure except corner cracks. When the strain rate is between 26.92 s⁻¹ and 56.18 s⁻¹, the failure mode of the specimen is axial splitting failure, and when the strain rate is 67.34 s⁻¹, splitting and shearing failure occur. With the increase of the strain rate, the growth rate of the dynamic compressive strength slows down. Compared with static compressive strength, the strength factor increases from 1.15 to 4.19. Also, the fractal dimension shows a gentle increase. When $Df$ is in the range of 1.82~2.24, there is a sudden change in fragmentation when the strain rate is in the range of 34.70 s⁻¹~56.18 s⁻¹. Energy dissipation density increases logarithmically with the strain rate. The results reveal the dynamic breaking and energy consumption laws of metamorphic limestone under impact loads with different strain rates and could provide some reference value for the safe and efficient construction in the Dahongshan mining area and similar engineering projects.

SHPB test system was used to conduct dynamic impact experiments on frozen granite under different negative temperatures. The fracture surface of granite under impact load was found via scanning electron microscope (SEM). The micromorphological characteristics of rock fracture under negative temperature are analyzed to explore the influence of negative temperature on the rock fracture morphology, and a practicable explanation is given for the mechanical property changes of rock under different temperatures. Research results showed that low temperatures (<-20°C) caused “frostbite” in granite, leading to a sharp decrease in the rock dynamic mechanical strength under a high strain. Fracture morphology analysis indicated that the lower negative temperatures resulted in the formation of cracks among the mineral particles in the granite. These cracks have poor plastic deformation ability and are easy to destabilize and expand under a high strain rate. Moreover, the coupling effect of impact and negative temperature will cause the cleavage of some crystalline minerals, eventually resulting in the low-stress brittle failure of granite. It is considered that the nucleation of cracks in negative temperature rock under impact load is mainly caused by crystal deformation, which can be divided into three types: the nucleation of cracks resulted from elastic incompatibility between the grains, the nucleation of cracks caused by interface slip, and the nucleation of cracks caused by plastic deformation in crystalline solid.