ROCK MASS CLASSIFICATION Assessment of rock mass strength recognizes cumulative effect of different geological features. Classification is therefore an accumulation of weighted values given to selected parameters. Two most widely used systems are the Geomechanics RMR system which adds rating values, and the Norwegian Q system which multiplies rating values. Both systems are dominated by fracture properties. Applications to specific engineering problems where rock mass class gives approximate guideline values of ground parameters, as in the lower table. Geomechanics System of Rock Mass Rating (RMR) uses parameters and point scoring, as in table below. Norwegian Q System successfully multiplies rating values to determine the rock mass quality (Q) as:

Q (RQD/Jn) (Jr/Ja) (Jw/SRF) Factors with rating ranges from good to bad are: RQD Rock quality designation 100-10 Jn Joint set number 1-20 Jr Joint roughness factor 4-1 Ja Joint alteration and clay fillings 1-20 Jw Joint water inflow or pressure 1-0.1 SRF Stress reduction factor due to

excavation 0.5-400 Q values range from 0.01 to 100. System is tabulated in the appendix (section 40).