Table 1.

Rock mass classification based on rock quality designation (RQD), permeability and rock mass rating (RMR)

%RQDDescriptionLugeon valuesDescriptionRMRDescription
90–100Excellent0–3Impermeable<20Very weak
75–90Good3–10Low permeability21–40Weak
50–75Fair10–30Medium permeability41–60Fair
20–50Poor30–60High permeability61–80Good
<25Very poor>60Very high permeability81–100Very good

Deere (1989, Ewert (1985) and Bieniawski (1989).