Characterization of jointed rock masses for geotechnical classifications utilized in mine shaft stability analyses

Abstract

In the Divriği open-pit iron mine in Turkey, extracted ore is initially crushed in an underground chamber. This chamber was previously located 54m below the bottom level of the mine, which was linked by a vertical shaft. Because of the progression in the mine operations, the mine management decided to shift the chamber to a depth of 264.15m below the surface. A borehole called as YNK-3, which was no closer than 15m to the existing shaft that was 4m in diameter and 54m in length, was drilled to a vertical distance of 264.15m. Although the first 54m was drilled in a coreless manner, the drill cores obtained from the remaining 210.15m were used in the rock mass characterization studies for the design of the shaft support. The rock formations encountered during shaft sinking, which were generally jointed rock masses, were classified into structural regions and domains for geological and geotechnical definition. Initially, the original rock mass rating (RMR) and quality (Q) systems were used for rock mass characterization, but difficulties were experienced in determining a number of input parameters required, particularly by the RMR system. A comprehensive examination of the drawbacks encountered directed us to the modified RMR (M-RMR) system. In this paper, the original (RMR and Q) and modified (M-RMR) rock mass classification systems are compared in a detailed discussion of our results. In addition, the classification results were tested using the Hoek-Brown failure criterion to compare the ratings presented by classification systems.