Updated rock mechanical design criteria for the Liikavaara Östra open pit

Abstract

The assessment of rock mechanical data is a fundamental step in the process of evaluating the profitability of an open pit mine. The steepness of bench, interramp and resulting overall slope angles have a direct effect on the stripping ratio, therefore on the profitability of the mining operation. With the recently challenging metal prices in mind, the maximization of slope angles is even more important nowadays, prompting detailed investigations in the topic.

The primary goal of this master thesis is to provide updated rock mechanical design criteria for the Liikavaara Östra open pit in Northern Sweden, by collecting and assessing the already available information from the area, as well as evaluating the raw data of the drilling campaign undertaken in 2016.

After the compilation of the rock mechanical and geological data of the site, the bench scale slope stability was assessed with probabilistic and deterministic approach. During the process, two failure criteria (Mohr-Coulomb and Barton-Bandis) and two groundwater conditions (drained and undrained) were tested. Based on the gained experience in the neighboring Aitik mine, the drained Barton-Bandis scenario was used both in probabilistic and deterministic approach to recommend bench face angles. Based on the findings of the bench slope analysis, an increase of the bench and interramp angles (compared to the previous design study) is possible, with the presumption of improved smooth blasting techniques and minimized back break. In identified areas with excessively poor rock quality, the application of external rock support was assessed in order to maintain reasonable bench angles and avoid mining of additional waste rock. The application of external slope support practices deemed feasible in the footwall domains of the pit, where with the utilization of support methods, the possible relocation of the E10 road can be avoided. The overall slope stability was also assessed in the footwall with limit equilibrium analysis methods. The footwall of the pit was found to be stable with the new design criteria, although it is sensitive to the presence of groundwater pressures.