# Investigating an Enhanced Contour Blasting Technique Considering Rock Mass Structural Properties
## 4 Conclusions  
In this study, a contour blasting design in underground excavations was proposed. The design parameters were optimized based on the rock's structural properties with the aid of numerical simulations. Unlike the standard blasting passport in use in the Akbakai mine, low-brisance explosives were used in the proposed contour blasting, which was tested in experimental blasting carried out in two development drifts. Both designs were implemented for a 9 m\({}^{2}\) cross-section area drift. A total of 37 blast rounds from each design approach were carried out, and the excavation profiles were surveyed to determine the amount of overbreak. The overall results indicated a substantial overbreak reduction in the excavation and the induced fractures of the surrounding rock mass. 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%. However, with the suggested contour blasting, the overbreak was less than 13%.  
The scheme of charging of contour blast holes considering the structural and strength characteristics of the rock mass was developed. This allowed for a reduction in overbreak around the excavations, which in turn improved the stability of the surrounding rock mass and increased the profitability of mining operations. However, these results were obtained for specific rock mass conditions (\(GSI=68\)). Adjustments and engineering judgment would be needed to implement the proposed design for other rock mass conditions. With the use of the proposed blasting design, the surface of the excavation showed a better appearance, with a smoother texture and no noticeable fractures or wedges. The blast hole traces from  
Figure 6: Excavation surface appearance: (**a**) rougher surface in conventional blasting; (**b**) smoother surface in the proposed contour blasting.  
the drilling were still visible along the drift, indicating a reduced impact of the blast load on the surrounding rock.  
During the pilot, we observed a significant reduction in intensive crack formation--along with the costs for the haulage of excess rock mass, the dilution of the mined ore, and other operational costs--when using low-brisance explosives in contour boreholes. It is concluded that the proposed contour blasting design can be implemented for mine drifts and other horizontal excavations driven in a competent rock mass with few joint sets, as the overall performance of the blasting showed improvement in comparison with the conventional method. Nevertheless, it is important to further investigate the development of guidelines for designing blasting passports using these explosives for various rock mass conditions.  
Conceptualization, A.I. and A.C.A.; methodology, A.M.; validation, A.I., A.M. and A.C.A.; writing--original draft preparation, A.M.; writing--review and editing, A.I. and A.C.A.; supervision, A.I.; revision, A.C.A.; project administration, A.I.; funding acquisition, A.I. All authors have read and agreed to the published version of the manuscript.  
This research was funded by the Ministry of Higher Education and Science (MHES) of the Republic of Kazakhstan, grant number AP22787307, and the APC was funded by AP22787307.  
Not applicable.  
The data presented in this study are available on request from the corresponding author. The data are not publicly available due to privacy.  
The authors wish to acknowledge the support of the authorities of the Akbakai mine for this study.  
The authors declare no conflicts of interest.