Evaluating the relationship between RMR and Q-system for improved classification of faulted rocks and weak rocks

Rock mass classification systems play a critical role in tunnel excavation and support design by evaluating key parameters such as uniaxial compressive strength, discontinuity conditions, and groundwater conditions. To improve reliability, multiple classification systems, particularly RMR and Q-System, are often utilized together. However, existing correlation equations between RMR and Q are generally derived from datasets representing intact rock masses and may not adequately capture the geological complexities of faulted zones. This study aims to establish new site-specific correlation equations for faulted and weak rocks using geological survey data from tunnel excavation sites in the Ulsan and Gyeongju regions of South Korea, where fault zones are prevalent and classification accuracy is critical due to the proximity to nuclear infrastructure. Regression analyses yielded the equations RMR = 2.2lnQ + 22.4 for faulted rocks and RMR = 4.5lnQ + 40.9 for weak rocks, with determination coefficients (R²) of 0.65 and 0.48, respectively. The results confirm that existing generalized equations may fail to accurately estimate ground support requirements in faulted conditions. These findings contribute to improved classification reliability and safer tunnel support design strategies in geologically complex environments.