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:
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.
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