Rock quality designation

Rock Quality Designation (RQD) is an index of assessing rock quality quantitatively. It is a more sensitive index of the core quality than the core recovery. The RQD is a modified percent core-recovery, which incorporates only sound pieces of core that are 100 mm (4 inch) or greater in length along the core axis. There are several methods to measure RQD, such as direct, indirect, and weighted joint density measure. The weighted joint measurement method is developed to achieve better information from borehole and surface observations. In principle, it is based on the measurement of the angle between each joint and the surface or the drill hole. The evaluation of weighted joint density requires small additional effort over currently adopted logging practices. The only additional work is to determine, which angle interval the intersection between the observation plane and each joint belongs. The angles chosen for the intervals between the joint and the drill hole are familiar to most people, and this makes the observations for wJd quick. The use of only four intervals makes the registration simple and easy.