Leeb Hardness Testing for Rock Strength Estimation: A Case Study from the Bingham Canyon Mine

ABSTRACT: Understanding rock strength is essential for assessing mine stability. Uniaxial Compressive Strength (UCS) is a critical measure of rock strength, though the frequency of laboratory testing is typically limited due to cost and time constraints. Rock hardness (R-value) is often used as a first order estimate of UCS in mining rock mechanics. R-values are measured using qualitative assessments with the geologic hammer and are easy to collect but inherently subjective. Additionally, Point Load Testing (PLT) provides a strength index that can be correlated with UCS values, but the test is destructive, and can be time-consuming. Originally developed for the metals industry, the Leeb Hardness (LH) tester offers a rapid, quantitative, safer, hand-held and non-destructive alternative for measuring rock hardness. While LH data will not replace the need for UCS testing, the high-density nature of LH data also makes it ideal for predictive modeling and as a reliable input for 3D geotechnical models. This study utilizes drill core data from the Bingham Canyon Mine and focuses on establishing a correlation between LH values, traditional hardness estimates (R-values), and PLT data using linear regression and correlation coefficient analyses for each rock type. Analyzing the Quartzite (QZ) and Monzonite (MZ) data, LH showed moderate correlations with PLT. Trends in data infer PLT values underestimate strength compared to LH, however limitations for the LH tester are also explored and discussed in this study. Future work will focus on developing the LH-UCS correlation for the specific lithologies present at Bingham Canyon, enabling more accurate geotechnical characterizations and informing stability assessments for ongoing and future mining operations.