Case Study: Investigation, Analysis and Mitigation of Rock Instability for a Potential Slope Failure in Highly Weathered Granite at Pinto Valley Mine in Arizona

ABSTRACT: In the mining and civil engineering industries, slope stability issues have become essential problems to avoid ensuring site safety, maximum ore extraction and limited interruptions in production. Slope failures in mining operations are a cause for concern when dealing with potential safety hazards, accidents and injuries for mining personnel and damage to equipment. Predicting, monitoring and investigating slope failures are pertinent for safe working conditions and should be inspected continuously. A high wall composed of a small top layer of alluvium underlined by highly weathered granite at the Pinto Valley Mine in Arizona expressed warning signs such as rockfall, talus/debris retained on lower benches, tension cracks and displacements on the slope stability radar (SSR) during production adjacent to the slope. Detailed inspections, monitoring and mitigation were immediately initiated following these signs of instability. If the area of interest is not critical to production, the easiest plan of action would be to leave the material in place and let the slope fail naturally as long it will not cause any safety hazards; however, this is not the case for failure researched in this paper. Mine blasting and production need to continue below the failure due to high grade ore in the vicinity. This can only happen if the failure mechanism is well understood and the rate of displacement is low. This study was performed to understand the mechanisms that triggered the failure, the rock conditions before and after the failure and to show how to proceed with controlled mining procedures in organized manner. This study will show observations before, during and after the slope instability as well as successful mitigation efforts and analyses. The results acquired illustrated that slope instability can be predicted from SSR, the SRR exhibited real time monitoring and provided initiation for mining safety protocols and procedures. 1. INTRODUCTION Slope stability plays an important role in rock engineering. During the design, construction and post design phases of rock slope stability, engineers and geologists need to pay close attention to the rock conditions within the rock slope to prevent slope failures, protect employees and maintain economic profit. Slope geometry, material properties, and insitu stress conditions need to be investigated in order to understand the potential for rock slides, wedge failures, and other instabilities.