Feasibility Study of a Continuous Borer-Bolter in an Underground Potash Mine

Abstract

Potash mining in Saskatchewan is most commonly done using one of two underground dry mining techniques: A variation of room and pillar mining, and stress relief mining. The potash ore that is mined has a large areal extent, is located at great depths, and is typically flat lying. However, some pockets in the ore body vary from the general geology, and are called anomalous. These areas can result in reduced stability from what would normally be found in the typical geological conditions. Potash mines install rock bolts in anomalous ground conditions to counter this. This is currently done using two different machines and results in a lot of down time for the mining operation. It has been theorized that by combining the two machines into one, time can be saved from the current process and result in increased stability of the mine back. This study pertains to the feasibility of attaching a bolting system to the back of a continuous boring machine for excavating anomalous ground conditions in underground potash mines. Three parts of this are examined: an estimate of the time saved by changing bolting methods, the change in mine roof stability due to the different bolting method, and the feasibility of crafting a machine that can fit in the confined space required. Bolting procedures are examined using individual task rates and projected for the proposed bolting methods. The change in stability that results from changing the bolting procedure is analyzed using finite element analysis. Finally, a concept machine is devised to show the ability to put such a bolting machine in the confined spaced available, and therefore showing the possibility of implementation. The geometric constraints, determined by a theoretical system, were used to create several feasible processes for installing bolts from the boring machine. This resulted in four potential variations in the process with regards to both the potential saved time and the stability of the tunnel. It was found that the potential for time savings were very large, with up to 72% of the current bolt process time being saved in some situations. It was found that the largest part of the mining process in poor ground conditions is spent on the installation of bolts, and therefore the most time was saved by methods capable of bolt installation while the boring machine was in motion. Based on modelled stress metrics in areas requiring support, the current support measures appear more effective than the proposed bolting procedure. The analyzed stress metrics were still improved when compared to an unbolted ground scenario; Similar values of simulated curvature and displacement were found in the tunnel back at lower disseminated clay heights when partially bolted than were observed when the simulation was unbolted. This study shows the borer mounted bolter can be considered an advantageous mining method for efficiency purposes in poor ground conditions and could potentially be suitable in some geological conditions, but likely should not be used in all anomalous ground scenarios.