Determination of rock quality designation (RQD) in metamorphic rocks: a case study (Bayburt-Kırklartepe Dam)

Abstract

The role and importance of rock mass classification systems from past to present in engineering designs are indisputable. Therefore, the correct estimation of the parameters that make up these systems is essential in terms of reliability, time, and economy. One of the crucial parameters commonly used in rock mass classification is the rock quality designation (RQD). This study aimed to indirectly estimate the RQD value determined from the core samples obtained from the exploration drillings. In this context, P wave velocity (V_p) was obtained by seismic refraction tomography (SRT) from the geophysical measurements applied in the metamorphic rock mass, and the discontinuity frequency parameter was obtained from the line survey studies carried out on the rock mass. What determined RQD values with the help of simple regression analyzes and empirical equations with high estimation capacity using V_p and discontinuity frequency parameters were obtained without drilling in the rock mass. Accordingly, the performance indexes of the equations produced by different researchers and the equations produced in this study were evaluated in determining the RQD parameter. In the generated equations, the highest coefficient of determination value depending on joint frequency and V_p wave velocity with RQD was calculated as R² = 0.89 and R² = 0.82, respectively. When the produced equations are evaluated according to the performance indexes, it is seen that the empirical equations obtained by previous studies have the highest root mean square error (RMSE) and values account for (VAF) values compared to the other equations and have very high estimation capacities. Thanks to the equations with high estimation capacity, the RQD value was determined depending on the joint density and V_p speeds.