Rock Quality Designation (RQD), was introduced by Don Deere in the mid-1960s as a means of using diamond core to classify rock for engineering purposes. Subsequently it was incorporated into the Rock Mass Rating and Q-system classification methods which, world-wide, now play substantial roles in rock mechanics design, whether for tunnels, foundations, rock slopes or rock
excavation.
It is shown that a key facet of the definition of RQD is ignored in many parts of the world, and it is noted that there are several inherent limitations to the use of RQD. Based on mapping of rock formations by seventeen independent professionals at different locations in Australia and South Africa it is shown that differences in assessed RQD values result in significant errors in computed RMR and Q ratings, and also in Geological Strength Index (GSI) and Mining Rock Mass Rating (MRMR).