Experimental Study on Dynamic Mechanical Properties and Failure Characteristics of Dry and Saturated Granite Under Different Strain Rates

The stability of deep water-saturated rock masses under dynamic disturbance is crucial for the efficient development of deep geothermal resources. This study focuses on granite as the research object, using the Split Hopkinson Pressure Bar (SHPB) system to investigate the dynamic mechanical properties, energy dissipation, and failure characteristics of dry and saturated granite under impact loading, and to analyze the influence of water on the dynamic mechanical properties of granite. The results show that granite exhibits a Type II stress–strain curve (rebound phenomenon) at low strain rates, while at high strain rates, it exhibits a Type I stress–strain curve. The dynamic mechanical parameters of granite exhibit significant strain rate dependence, with water-saturated granite showing a stronger strain rate sensitivity. The dissipated energy and dissipation coefficient of the granite samples increase linearly and logarithmically, respectively, with the increase in incident energy. The dissipated energy of water-saturated granite is higher than that of dry granite. As the strain rate increases, the failure mode of the granite specimens transitions from splitting to fragmentation, with a more pronounced ductile fracture mode. The degree of fragmentation of water-saturated specimens is greater than that of dry specimens. As the strain rate increases, the difference in fractal dimensions between dry and water-saturated specimens decreases. At high strain rates, the free water within the rock generates inertial effects, meniscus effects, and viscous effects. When the strain rate reaches 124.22 s−1, the strength of the water-saturated specimen matches that of the dry specimen. The research findings provide theoretical support for the safe and efficient development of deep geothermal resources.