## 4 Results and Analysis of Impact Tests
### Mechanical Performance of Samples under Dynamic Loading  
On basis of the wave voltage signals monitored using the strain gauges and dynamic strain meter, the dynamic property parameters such as the incident, reflected and transmitted wave stresses, dynamic compressive strength, dynamic strain and with strain rate could be derived according to Equations (8)-(10). Figure 9 presents the typical dynamic-stress versus dynamic strain curves of the representative specimens for each group. On this basis, we can further calculate the dynamic elastic modulus, namely the tangent modulus of the point at 50% peak on the curve, as listed in Table 2. In addition, to find the law among the groups of specimens, we solved the average property parameters of each group of samples (see Figure 10). \begin{table}
\begin{tabular}{c c c c c c c c c c} \hline \hline
**Specimen** & **Length** & **Width** & **Height** & **Density** & **Hit** & **Dynamic** & **Dynamic** & **Peak** & **Strain** \\
**Number** & **/mm** & **/mm** & **/mm** & **/g\(\cdot\)cm\({}^{-3}\)** & **Velocity/** & **Compressive** & **Strength/MPa** & **Modulus** & **Strain/\%** & **Rate/s\({}^{-1}\)** \\ \hline G1-A & 45.7 & 19.8 & 45.6 & 2.44 & 10.05 & 180.50 & 22.99 & 9.18 & 64.65 \\ G1-B & 45.0 & 19.9 & 44.9 & 2.45 & 9.76 & 194.46 & 26.03 & 10.09 & 74.78 \\ G1-C & 45.1 & 20.7 & 45.2 & 2.47 & 10.18 & 185.11 & 30.60 & 7.48 & 50.67 \\ G2-A & 45.5 & 19.9 & 45.7 & 2.43 & 9.97 & 169.16 & 26.22 & 8.82 & 68.81 \\ G2-B & 45.1 & 19.8 & 45.1 & 2.43 & 10.27 & 157.36 & 25.44 & 8.21 & 79.52 \\ G2-C & 45.2 & 19.8 & 45.2 & 2.45 & 9.83 & 157.18 & 24.58 & 7.30 & 66.73 \\ G3-A & 45.0 & 20.1 & 45.1 & 2.43 & 9.96 & 173.29 & 22.47 & 9.64 & 75.42 \\ G3-B & 44.7 & 19.9 & 45.7 & 2.40 & 9.97 & 150.00 & 23.79 & 7.72 & 75.18 \\ G3-C & 45.1 & 20.0 & 45.1 & 2.44 & 9.92 & 173.20 & 24.35 & 9.35 & 75.50 \\ G4-A & 45.1 & 19.9 & 45.1 & 2.43 & 9.85 & 134.39 & 23.13 & 8.03 & 79.17 \\ G4-B & 45.0 & 19.7 & 45.0 & 2.42 & 9.89 & 131.61 & 25.50 & 6.87 & 76.29 \\ G4-C & 45.5 & 19.9 & 45.5 & 2.42 & 10.03 & 134.00 & 23.87 & 7.70 & 78.72 \\ G5-A & 45.0 & 19.7 & 45.0 & 2.44 & 9.92 & 139.88 & 27.84 & 7.26 & 75.89 \\ G5-B & 44.7 & 19.9 & 45.5 & 2.41 & 9.99 & 134.01 & 27.53 & 6.10 & 74.91 \\ G5-C & 45.1 & 19.8 & 45.1 & 2.43 & 9.94 & 138.94 & 25.37 & 7.72 & 76.12 \\ G6-A & 45.1 & 20.1 & 45.0 & 2.43 & 9.92 & 117.42 & 22.22 & 6.69 & 80.56 \\ G6-B & 45.1 & 20.1 & 45.1 & 2.43 & 9.86 & 117.22 & 23.14 & 6.49 & 79.53 \\ G6-C & 45.1 & 20.2 & 45.1 & 2.42 & 9.94 & 97.97 & 27.18 & 4.92 & 78.46 \\ D7-A & 45.1 & 19.7 & 45.1 & 2.42 & 9.96 & 127.49 & 26.40 & 6.40 & 75.32 \\ D7-B & 45.0 & 19.8 & 45.0 & 2.42 & 9.97 & 132.84 & 24.81 & 7.43 & 75.14 \\ D7-C & 45.1 & 20.0 & 45.1 & 2.43 & 9.96 & 118.21 & 25.81 & 5.82 & 68.50 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Mechanical properties of samples subjected to impact loads. Figure 9: Curves of dynamic stress versus dynamic strain. According to Table 2, we can calculate the average dynamic compressive strength of each group of specimens, namely, 186.69 MPa, 161.23 MPa, 165.50 MPa, 133.33 MPa, 137.61 MPa, 110.87 MPa and 126.18 MPa. It can be seen that the dynamic strength of each group of samples is different. Compared with the intact specimens, the dynamic compressive strength of the specimens of G2 to G7 drops by 13.64%, 11.35%, 28.58%, 26.29%, 40.61% and 32.41%, respectively. Apparently, the presence of the prefabricated holes significantly deteriorates the dynamic compressive strength of the rock, and the weakening influence is found to be associated with the quantity and layout of the holes. Among the pre-holed specimens, the strength order of each group of samples is: G3 > G2 > G5 > G4 > G7 > G6. For specimens with one, two, three or four circular holes, the dynamic compressive strength of the specimen basically declines with the rise in the number of holes. However, an interesting thing is that the dynamic compressive strength of the specimen with four holes is higher than that of the specimen with three holes.