# Study on Dynamic Loading Characteristics of Rock Containing Holes
## 4 Simulation Results and Analysis
### The Impact of Strain Rate on the Dynamic Mechanical Parameters of Rock Specimens  
To investigate how holes affect the dynamic mechanical properties of rocks under different strain rate conditions, data on dynamic mechanical strength and peak strain for specimens under various loading scenarios were compiled, as shown in Figures 12 and 13. The analysis of Figure 12 indicates that the correlation between the diameter of the specimen holes and their dynamic mechanical strength approximates a linear relationship, conforming closely to the linear equation (Y = a + bx). Furthermore, the dynamic mechanical strength and peak strain for all specimens in this study were observed to increase with strain rate, consistent with previous research findings. However, the sensitivity of both dynamic mechanical strength and peak strain in specimens with two holes to changes in strain rate decreases as the hole diameter increases, leading to less marked variations in dynamic mechanical strength and peak strain under different strain rate conditions. This effect becomes more pronounced with the enlargement of hole sizes.  
Figure 11: Dynamic stress–strain curves of double-hole specimens at different strain rates: (**a**) 2 mm hole specimen; (**b**) 4 mm hole specimen; (**c**) 6 mm hole specimen; (**d**) 8 mm hole specimen.  
Figure 12: Influence of strain rate and hole diameter on the dynamic mechanical strength of rock specimens: (**a**) single-hole specimen; (**b**) double-hole specimen.  
Previous studies indicate that the dynamic mechanical behavior of specimens with two holes is less affected by strain rates, though the precise mechanical explanations for this phenomenon remain elusive. However, certain investigations have pinpointed the critical role of the internal stress field's evolution under external forces in causing rock material failure. This research studies the evolution law of the stress field of test specimens with holes using a numerical model. For the single-hole specimen, concentric measurement circles with a radius of 2 mm were methodically positioned at 30\({}^{\circ}\) intervals around the hole's center, extending outward to a 6 mm radius, thus forming circular measurement zones. Conversely, in the case of double-hole specimens, an elliptical configuration for the stress field measurements was utilized, with uniform parameters set for tracking angles and radial distances.  
Figure 13(a) depicts the vertical stress field distribution around the borehole of a specimen with a single 6 mm hole, where the impact load direction is parallel to the X-axis. This orientation results in the highest stress concentrations at 90\({}^{\circ}\) and 270\({}^{\circ}\) from the borehole center, and the lowest stress at 0\({}^{\circ}\) and 180\({}^{\circ}\). Near the borehole's apex and parallel to the loading direction, the stress levels are low, while regions perpendicular to the load direction at the hole's apex register high stress. Drilling leads to a stress redistribution in the rock, causing stress to intensify from the borehole's apex in the X-direction towards the apex in the Y-direction. An increase in strain rate is associated with a rise in vertical stress intensity across various angles. In contrast, Figure 13(b) demonstrates that the stress at 0\({}^{\circ}\) and 180\({}^{\circ}\) remains minimal for a specimen with two holes, with a more uniform vertical stress distribution observed at other angles. With an escalation in strain rate, the vertical stress intensity at various angles tends to stabilize, indicating that under high strain rate conditions, the stress distribution in specimens with two holes becomes more uniform, devoid of significant stress concentrations.  
Figure 13: Influence of strain rate and hole diameter on the peak strain of rock specimens: (**a**) single-hole specimen; (**b**) double-hole specimen.