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Table 1: Comparison of two rock mass quality classification systems

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.

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.
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