2. ROCK QUALITY
DESIGNATION
➢ RQD is the sum of lenght (between natural
joints) of all core pieces more than 10cm long
as a percentage of the total core length.
➢
➢ Equation of RQD
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3. Table of RQD
S.NO RQD ROCK QULITY CLASSIFICATION
1 < 25 VERY POOR
2 25-50 POOR
3 50-75 FAIR
4 75-90 GOOD
5 90-100 EXCELLENT
4. ➢ In the undergroud opening it is usually possible
➢ to gate a three dimensional view of rock mass
➢ a three dimensional RQD may therfore be used.
➢ The following formula may be used
➢
➢ RQD = 115 – 3.3 Jv
➢
➢ where jv is number of joints