RQD is an acronym for a technique that is used in geotechnical engineering principles in which that determines the quality of rock that was recovered when taking a core sample. It means rock quality designation and representative cross sections of the core sample must reach, or exceed 90- 100 mm in length for it to be considered excellent in quality. An RQD index is listed below .
RQD is defined as the quotient:
From the RQD index the rock mass can be classified as follows: