Rock Mass Classification System Used for Pahang-Selangor Raw Water Transfer Tunnel

Abstract

The recent Pahang-Selangor raw water transfer tunnel project had resulted in a large amount of rock mass classification data for the assessment of the rock mass class required for the design of tunnel support system. In this project, a rock mass classification by Japan Highway Public Corporation (JH) has been used to assess the rock mass class using geological mapping and geological documentation of the tunnel face and the side walls of the excavated tunnels. Although JH classification had been used for this project, other forms of classification using different criteria from Rock Mass Rating (RMR) and Q-System have also been widely used for tunnelling project all over the world. Since there have been few studies on the relationships among such different criteria of the classification systems, this study mainly focuses on the comparison between the JH and RMR classification systems for the water transfer tunnel. From the correlation analysis among the criteria used in both JH and RMR classification systems, there is higher correlation if the rock mass is in relatively good condition. It was also found that there is less consistency between JH and RMR classifications in the region of ‘poor rock’. However, the correlation between both classification systems is still considered suitable to be used in this tunnelling project.