Rock Quality Designation
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Rock Quality Designation (RQD) was developed in 1964 by D. U. Deere. It is based on measuring core recovery percentage which incorporates only pieces that are greater than 100 mm in length. In this respect pieces of core that are not hard and sound should not be counted though they are 100 mm in length. The optimal core diameter is 47.5 mm. RQD has considerable value in estimating support of rock tunnels. This quantitative index has been used as a red flag to identify low-quality rock zones. Today RQD is used as a standard parameter in drill core logging and forms a basic element value of the major mass classification systems: Rock Mass Rating system (RMR) and Q-system
[edit] Definition
RQD is defined as the quotient:
*100%- (Sumof10) = Sum of length of core sticks equal to and longer than 10 cm
- ltot = Total length of core run
[edit] Classification table
From obtained RQD index we can classify rock mass:
| RQD | Rock mass quality |
|---|---|
| <25% | very poor |
| 25-50% | poor |
| 50-75% | fair |
| 75-90% | good |
| 90-100% | excellent |
