# Blasting of Unstable Rock Elements on Steep Slopes
## 4 Discussion  
Generally, a good match between the real (PFr) and calculated (PFe) powder factors can be observed. The only exception is case study n. 2 from Quebec. The PFr used in this case is much higher than in other cases and has already been reported as anomalous [21]. In order to make the various PF values comparable, they are normalized to the empirical coefficients R, E, F, and D.  
Figure 8 shows the normalized values of the real powder factor PFr and the calculated power factor PFe as a function of the ratio between the spacing of the drilled holes along the same row and the selected borehole diameter. The trend of the normalized PF values is represented by the line of equation PF = 0.0059 * (spacing/drilling diameter) + 0.0009. The PF obviously increases with the increase in the ratio between the spacing and diameter of the hole. The latter varies in the range 24-40, which is in good agreement with field experiments in the literature [22; 23]. It should be outlined that demolition for securing a slope can follow different partial goals: cases n.3 and n.4 were finalized with a driven fragmentation in order to protect the road pavement, while in case n.5, the aim was the removal of huge unstable and distressed rock elements, with little concern for the size of fragments--something that should have be flagged regarding hazards during drilling by the rock climbers. Comparing the proposed solution for the blasting of impervious and critical portions of rock slopes with current blasting schemes or other solutions (reinforcing or protection), it appears that this study can help improve the efficiency of results, optimize the consumption of explosives, reduce excess vibration and fly rocks, and enable such operations to occur in safer working conditions: more care put into investigating the rock mass structure and blasting scheme turns into improved final results. For example, in terms of local geostructural characterization, seismic surveys, specifically where the installation of a geophone array becomes possible, should help to detect possible hidden persistent joints at the rear, even if P-wave velocity detection alone does not appear sufficient to evaluate and classify rock masses, because characteristic impedance may be taken as a comprehensive index to evaluate and classify rock masses [24], as it is evident that the properties of rock formations constitute a decisive factor in determining the parameters of drilling \begin{table}
\begin{tabular}{c l c} \hline
**Class** & **Fragmentation** & F \\ \hline
1 & normal (several blocks bigger than 1 m\({}^{3}\)) & 1.00 \\ \hline
2 & high (maximum size up to 1 m\({}^{3}\)) & 1.20 \\ \hline
3 & very high (maximum size up to 0.5 m\({}^{3}\)) & 1.40 \\ \hline \end{tabular}
\end{table} 
Table 4: Increase in FP to achieve greater fragmentation. \begin{table}
\begin{tabular}{c l c} \hline
**Class** & **Displacement** & **D** \\ \hline
1 & no additional displacement in addition to the action of gravity & 1.00 \\ \hline
2 & additional displacement required (few meters) & 1.20 \\ \hline
3 & high additional displacement required (10 m or more) & 1.60 \\ \hline \end{tabular}
\end{table} 
Table 5: Increase in FP to obtain displacement of blasted rock. and blasting operations [25]. Valuable data from the multichannel analysis of surface waves (MASWs) could be used for the selection of explosives with the desired velocity of detonation and density, so as to match the impedance of rock mass [26]; these data could also be used with the development of algorithms to match the relevant impedance for selecting the right type of explosive [27]. Using explosives to remove unstable rock elements on rocky slopes presents a viable and often efficient solution for enhancing safety conditions. This method offers advantages in terms of speed, cost-effectiveness, and minimal subsequent maintenance interventions compared to alternative techniques.