Table 1: Comparison of two rock mass quality classification systems
| Rock Mass Quality |
Classification according to Reference Ground Conditions in Tender Documents |
Classification according to the Contractor |
| Q1 Very Good |
Massive, Jv<5, Conditions of discontinuity FC=1 - 2. No significant weathering. High Strength |
Distinction betweenQ1 and Q2 is largely based on judgment |
| Q2 Good |
Low to Moderately joint frequency, 5<=Jv<=20. Conditions of discontinuity FC = 2-3. High strength. Low to moderately spalling in Q1Q2 rock. |
Distinction between Q2 and Q3 is mainly done on degree of weathering |
| Q3 Fair |
Moderately to highly jointed, 10<=jv<=20. Conditions of discontinuities FC=3. Slight weathering may occur. Moderate to high intensity spalling in Q1-Q2 rock |
Distinction between Q3 and Q4 is done on the basis the basis of fracture condition FC, and degree of weathering |
| Q4 Poor |
High joint frequency, jv>=20. Conditions of discontinuity FC = 3-4. Moderately to highly weather rock. High to very high spalling intensity in Q1-Q2 |
Any 5 m section intersected by a fracture with wall separation > 1mm (FC=5 or 6) or any 5 m section within moderately weathered rock |
| Q5 Extremely Poor |
Large fault zones involving swelling and squeezing rock. Conditions of discontinuity FC=4-5 |
Distinction between Q5 and Q4 is done on the basis of degree of weathering. |
| Key: |
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Jv is the sum of the number of joints per unit length for all joint (discontinuity) sets known as the volumetric joint count. RQD = 115 3.3Jv according to Palmstrm (1995).
FC= conditions of discontinuities as per Geomechanics (RMR) Classification for jointed rock.
