Development of a new empirical relation between RMR and Q rock mass classification systems

Rock mass classification is one of the most important and practical criteria in designing of underground excavations and estimating the related support systems. RMR and Q classifications are the most utilized rock mass classification systems in which different geological surveys and rock mechanics studies have been required for precise determination of their numeric values. Considering the significance of these two classification systems, costly and time-consuming process of data collection in order to determine the required parameters to calculate these systems, development of valid relations between the above classification systems is essential. In this research, different empirical relations in the forms of linear, polynomial, exponential, logarithmic and power equations between the RMR and Q classification systems are firstly developed based on the measured data in the several parts of the Marivan Azad dam tailrace. Then, the logarithmic relation is proposed as the most precision and reliable empirical relation between the above classification systems based on the determination coefficient criterion, significance level and F-test in the ANOVA. Proposed relation is similar to the Bieniawski equation but some modifications have been made in its coefficients for localization and obtaining the better results. Finally, results verification using the evaluation performance indices showed that estimation accuracy of the proposed relation and its conformity with the measured values are better than those of the previous relations and has the higher conformity with the measured data.