# Investigating an Enhanced Contour Blasting Technique Considering Rock Mass Structural Properties
## 3 Results and Discussion
### Blasting Results  
The blasting passport was developed according to the proposed design along with the trial blasting results. We determined that we should place supplementary empty blast holes in the vault to disperse the explosion's force, thereby mitigating its impact on the excavation. The results of the numerical simulations also served as guides and helped adjust the design. Figure 2 illustrates the blast hole layout scheme. The distribution system of emulsion explosives with a hose diverter is currently commonly used in foreign practice. This system has demonstrated a variety of benefits, such as enhancing the effectiveness of the mining operations, reducing the time required to charge the working face, and reducing manual labor. Nevertheless, in the context of Kazakhstan, the cost of emulsion explosives is more expensive than the explosives suggested by the authors from an economic perspective. The authors' proposed charging scheme involves the use of ammonium nitrate, detonating cord, and detonator primer as explosive charges in the contour boreholes. This approach to charging contour boreholes yields highly effective outcomes that are intended to control the damage zones of rock mass during contour blasting. Figure 2 illustrates the charging contour borehole scheme. Figure 4 provides an example of the actual surveyed cross-sections of excavations corresponding to the standard blasting design (Figure 4a) and the charging contour blast  
Figure 3: Simulations of the stress states around the excavation cross-section: (**a**) using the conventional method of blasting; (**b**) using the proposed contour blasting. holes proposed in this study (Figure 4b). The observations indicated that the actual cross-sectional area of excavations using the conventional method of blasting was equal to 14.1 m\({}^{2}\), while the cross-sectional area of the proposed design was 12.0 m\({}^{2}\). As shown in Figure 4a, the conventional blasting method results in fracturing and failures in the roof and walls of the excavation, leading to an increase in the excavation overbreak (excess section ratio) of at least 17.5%. Meanwhile, Figure 4b shows an average overbreak of less than 5% in the contour blasting, suggesting a close alignment between the excavation's contour and the designed excavation profile. This contour blasting design was further tested, and experimental blasting was carried out in two excavations (development drifts) in two adjacent sublevels with a cross-section of 9.0 m\({}^{2}\). The rock mass properties were identical for both excavations. The upper blasting was carried out in the conventional way, and the lower excavation used contour blasting. A total of 37 blast rounds from each design approach were carried out over 1.5 months. After each blast, the cross-section of the excavation was surveyed with a laser total station. The survey results are summarized in Figure 5. As can be seen, the cross-section of excavation with the conventional blasting method varied between 10.5 and 12.1 m\({}^{2}\), indicating an overbreak between 17 and 34%. With contour blasting, the maximum actual cross-section of excavation that was observed was 10.2 m\({}^{2}\) (or 13% of overbreak). For example, in the first blasting round (R1), the overbreak was 12% and 2% in the conventional (standard) blasting. It is worth mentioning that a few cases of underbreak were noticed while using the proposed contour blasting. Nonetheless, the outcomes of the trials conducted at the Akbakai mine after three months demonstrated favorable results. This has been proven by the decrease in excessive fractures and fissures in the rock mass compared to the conventional  
Figure 4: Profiles of the surveyed excavations blasted using (**a**) conventional blasting and (**b**) the proposed contour blasting. Figure 5: Overbreak distribution along the excavations after 37 rounds of blasting. blasting method used in that mine. Therefore, it can be concluded that the proposed contour blasting achieved a reduction of the impact of blasting on the rock mass.