What is Rock Quality Designation (RQD)?

Rock Quality Designation (RQD) is specifically defined as a percentage of unfragmented drill core lengths from a core sample, typically taken during geological exploration. It is used to characterize the quality of rock, particularly in terms of its integrity and suitability for various engineering projects. RQD is calculated by taking the length of core pieces that are at least 10 centimeters long, dividing it by the total length of the core run, and then multiplying by 100 to express this as a percentage.

This measure is critical in geotechnical engineering, as it provides insight into the conditions of subsurface rock formations. Higher RQD values indicate better intactness of the rock, which generally correlates with greater stability and lower likelihood of rock failure in structural applications. In contrast, lower RQD values suggest a greater degree of fragmentation, which can be indicative of poor rock quality for construction purposes.

The other choices do not capture the essence of RQD. While rock density and porosity are important physical properties, they do not directly relate to how well a rock can be expected to perform in engineering contexts in terms of unbroken core length and structural integrity. Additionally, while rock soundness pertains to the durability of the rock, it is a separate concept that does