## 4 Discussion
### Pattern of joints  
Results of the SHPB test for the planar joint specimen and the sawteeth joint specimen reveal the influence of joint pattern on the dynamic characteristics of a jointed rock mass. Figure 10 plots the dynamic peak stresses for jointed specimens that have total angles of \(\beta+\alpha=45^{\circ}\) and \(51^{\circ}\). The maximum angle of application of the load to the joint surface for the sawteeth joint specimen that has \(\beta=39^{\circ}\) and \(\alpha=6^{\circ}\)equals that for the planar joint specimen with a joint angle of \(45^{\circ}\). Nevertheless, these two specimens have different outcomes (Figure 10a). When slide failure occurs, the planar joint specimen exhibits a lower slope of the relationship between the dynamic peak stresses and loading rate than those of the sawteeth joint specimen. The upper bound on the loading rate that causes sliding between the two parts of the planar joint specimen is also lower than that of the sawteeth joint specimen. When fracture failure happens, the slope of the relationship between the dynamic peak stress and the loading rate for the planar joint specimen is close to that for the sawteeth joint specimen (Table 4).  
\begin{table}
\begin{tabular}{c c c c} \hline \hline  & **Slide Failure** & **Fracture Failure** & **Crushing Failure** \\ \hline Loading rate & \(\oplus\) & \(\oplus\) & \(\oplus\) \\ Base plane angle & \(\bigcirc\) & \(\bigcirc\) & X \\ Asperity angle & X & \(\bigcirc\) & X \\ \hline \hline \end{tabular} Remarks: \(\bigcirc\) presents significant factors with 90% level of significance, among which, \(\oplus\) indicates the primary factor. X presents insignificant factor.  
\end{table}
Table 6: Significant factors affecting the dynamic peak strength for various failure types.  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline  & **DF** & **SS** & **MS** & **F** & \(\boldsymbol{p}\) \\ \hline Regression & 3 & 47,244.38 & 15,748.13 & 257.22 & 0.00 \\ Residual Error & 108 & 6612.20 & 61.22 & & \\ Total & 111 & 53,856.58 & & & \\ \hline  & **Coef** & **SE Coef** & **T** & \(\boldsymbol{p}\) & **90\% CI** \\ \hline Intercept & 56.35 & 0.74 & 76.22 & 0.00 & (55.12, 57.58) \\ Loading rate & 20.30 & 0.75 & 27.00 & 0.00 & (19.06, 21.55) \\ Base plane angle & 2.40 & 0.77 & 3.13 & 0.00 & (1.13, 3.68) \\ Asperity angle & 3.09 & 0.77 & 4.03 & 0.00 & (1.82, 4.36) \\ \hline  & & \multicolumn{4}{c}{\(R^{2}=0.877\), \(R_{\text{all}}{}^{2}=0.874\).} \\ \end{tabular}
\end{table}
Table 5: Results of analysis of variance (ANOVA) for specimens with fracture failure.  
The sawteeth joint specimen that has \(\beta=45^{\circ}\) and \(\alpha=6^{\circ}\) and the planar joint specimen with a joint angle of \(51^{\circ}\) yields similar results. The planar joint specimen has a smaller slope of the relationship between the dynamic peak stresses and loading rate, and a lower upper bound on the loading rate that causes slide failure. The planar and the sawteeth joint specimens have similar slopes of the relationship between the dynamic peak stresses and loading rate when fracture failure happens (Figure 10b and Table 4). Remarkably, the sawteeth joint specimen with \(\beta=39^{\circ}\) and \(\alpha=12^{\circ}\) fails only by fracture and not by sliding at a low loading rate. These experimental results indicate that the combination of \(\beta\) and \(\alpha\) angles influence not only the relationship between the dynamic peak stresses and loading rate, but also the failure types of jointed specimen under various loading rates, for a particular maximum angle of application of the load to the joint surface of the specimen. The triangular sawteeth with an asperity angle of \(6^{\circ}\) provides more friction than the planar joint with a similar angle of loading, leading to a higher dynamic peak stress when slide failure occurs.