Document Type : Original Research Paper
Author
North Khorasan Province Official Experts Association, Iran
Abstract
Rock mass characterization is essential for safe and economical design in mining, tunneling, and slope engineering. The Geological Strength Index (GSI) and Rock Mass Rating (RMR) are among the most widely used empirical rock mass classification systems. However, existing quantitative correlations remain limited by geological variability and inconsistent parameter definitions, reducing their transferability across different geological settings. This study develops an empirical relationship between GSI and the structural component of Rock Mass Rating, hereafter termed RMR_str, for carbonate and clastic rock masses in the Central Alborz geological zone. RMR_str was defined using only the structural parameters common to both systems, excluding intact rock strength and groundwater ratings. The study surveyed 134 field stations across the Elika, Lar, and Shemshak formations, recording the discontinuity parameters required to determine GSI and calculate RMR_str. Regression analysis produced the correlation GSI = 1.73696 × RMR_str − 9.54120 (R² = 0.9993), which remained stable under cross-validation, Monte Carlo simulation, and sensitivity analysis. To evaluate the model beyond the calibration dataset, it was independently tested using field data from the Bukan bauxite mine, where it demonstrated acceptable predictive performance. The resulting equation enables quantitative GSI estimation from routinely available RMR_str data, with a typical uncertainty of ±3.1 GSI units (1σ) within the validated range (25 ≤ RMR_str ≤ 50). Because GSI and RMR_str share common structural descriptors, part of the reported coefficient of determination reflects mathematical coupling rather than independent predictive capability. Consequently, application outside the Central Alborz geological zone requires independent validation.
Keywords
- Discontinuity Characterization
- Joint Condition
- Structural Parameters
- Monte Carlo Simulation
- External Validation
Main Subjects
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