Estimation of rock mass permeability using variation in hydraulic conductivity with depth: experiences in hard rocks of western Turkey

Determining permeability of fractured rocks is a focal point in engineering projects. Many methods have been developed for direct in situ determination of the hydraulic parameter; nevertheless, especially in the preliminary stages of rock mass characterization, empirical correlations are used to estimate the rock permeability. This study proposes a relationship between rock mass depth and permeability that may be useful for initial hydraulic characterization of fractured media. For this purpose, results of core drilling, injection tests, and geophysical prospecting carried out in fractured hard rocks—mainly andesites and secondly metamorphites—of western Turkey were considered. A decrease in rock mass permeability with depth is evident from the results of injection tests. Within the depth of investigation (the first 100 m), hydraulic conductivity shows an exponential declining trend with depth and depends on the surface value of the hydraulic parameter. No correlation is evident between discontinuity spacing and depth or rock quality designation (RQD) and depth. The applicability of the relationship found requires a hydrostructural homogeneity of the rock mass, which can be verified through inexpensive geological survey and geophysical prospecting.