Correlations between BQ and Q rock mass classification systems and design impact on a tunnel project in Malaysia

The design of primary and secondary support of a tunnel depends on the adequacy of the parameters derived from the ground model and used in the analysis. Standard practice in underground engineering is to refer to geomechanical rock mass classification systems to provide an empirical estimate, which can then be verified through analytical and numerical means. Based on 115 pairs of values obtained through ground investigation across eight tunnels totalling approximately 20 km in length, a statistical correlation between the Q system Tunnelling Quality Index ( Q system) and the Standard for Engineering Classification of Rock Masses (BQ system) was conducted for a granite rock mass in Malaysia. The purpose is to reveal the merits and limitations of each and discuss their similarities and differences. The methods and development of both rock mass classification systems are also compared. A linear correlativity of the uncorrected BQ value and the RQD/( J n SRF) (where RQD is Rock Quality Designation, J n is joint number and SRF is stress reduction factor) component of the Q system, with an R 2 of 0.68, is obtained. A breakdown of the reasons for the lack of correlation is presented, including the individual parameters of each system and the data collection method. The impact on proposed temporary support of applying previous correlations of the two systems is also discussed.