Volume 19, Issue 4 (December 1996)
Round Three—Repeatability and Reproducibility of RQD Values for Selected Sedimentary Rocks
A third round of study of the Interlaboratory Testing Program for Rock Properties (ITP/RP) of the Institute for Standards Research has produced precision measures for the Rock Quality Designation (RQD) index. Eight experienced participants determined the RQD index of four types of sedimentary rock (anhydrite/calcite, calcareous shale, limestone, and anhydrite) with four replications per rock type. The mean RQD indexes for the four rock types ranged from 60 to 92%. The normalized repeatability and reproducibility (r/¯x and R/¯x) for the four rock types range from 0.15 to 0.53 and from 0.15 to 0.66, respectively. The magnitudes of the repeatability r and the reproducibility R decrease with the increasing mean value ¯x of the RQD index. For three of the four rock types, the reproducibility R is equal to the repeatability r, that is, the variability among participants' results is no greater than the variability among replicate results from the same participant. The fourth rock type, for which R/¯x > r, is the calcareous shale; this is also the rock type with the smallest mean RQD index, ¯x, and the largest normalized repeatability and reproducibility, r/¯x and R/¯x. Because this study's range of mean RQD indexes is small, all of the rocks studied are sedimentary, and the number of participants making measurements is only slightly greater than the required minimum, the results of this work should be regarded as a first step in estimating the precision measures of the RQD index. Appended is a proposed precision statement suitable for inclusion in an ASTM standard on the determination of the RQD index.