Introduction
Rock Quality Designation (RQD) is a measure of quality of rock core taken from a borehole. RQD signifies the degree of jointing or fracture in a rock mass measured in percentage. It is commonly used in rock mass classification which is fundamental in tunnelling, dam construction, mine and slope design.
The RQD is given by the following formula:
RQD = (SUM (length of sound pieces >100mm)/Total core run length) x 100
The quality of the rock mass and the extent of fragmentation are measured objectively and quantitatively by the RQD index.
Application of RQD
In geotechnical engineering, RQD is an essential parameter with a variety of uses, such as:
Rock mass classification: The Q-system and the Rock Mass Rating (RMR) are two examples of systems that employ RQD as one of their parameters.
Rock Stability Analysis: By supplying data on the degree of fracture and the quality of the rock mass, RQD is utilised to evaluate the stability of rock slopes and underground excavations.
Geotechnical Design: RQD is utilised in the design of a variety of geotechnical structures, including underground mines, dams, and tunnels.
Rock Strength and Deformation: RQD is used to calculate the attributes of rock strength and deformation, including Poisson’s ratio and Young’s modulus.
Categories of Rock Masses based on Rock Quality Designation (RQD) Index
| Rock quality | RQD |
| Very poor (completely weathered rock) | < 25% |
| Poor (weathered rocks) | 25 to 50% |
| Fair (Moderately weathered rocks) | 51 to 75% |
| Good (hard rock) | 76 to 90% |
| Very good (fresh rocks) | 91 to 100% |
Conclusion
In geotechnical engineering and rock mechanics, the rock quality designation (RQD) index is a crucial metric for assessing the quality of rock masses. The quality of the rock mass and the extent of fragmentation are measured objectively and quantitatively by the RQD index. Based on the quality and degree of fragmentation of the rock mass, distinct groups are created using the RQD values.
By using the RQD, rock masses can be classified as extremely poor, poor, fair, good, or exceptional. Deere and Deere created the RQD index in 1967, and throughout time, a few additional authors have improved and adjusted it.
