This paper proposes a new application of the rock mass classification concept on the estimation of hydraulic conductivity of fractured rocks. The new rock mass classification system called as " HC-system" based on the following four parameters: rock quality designation (RQD), depth index (DI), gouge content designation (GCD), and lithology permeability index (LPI). HC-values can be calculated from borehole image data and rock core data. To verify rationality of the defined HC-system, the study collected data from the results of two hydrogeological investigation programs in three boreholes to determine a relationship between hydraulic conductivity and HC. Regression analysis was performed to estimate the dependence of HC on hydraulic conductivity. The regression results indicated that a power law relationship exists between the two variables with a coefficient of determination of 0.866. The regression equation provides a useful tool to predict hydraulic conductivity of fractured rocks based on measured HC-values. By using this regression equation, hydraulic conductivity data in a given site can be directly acquired, which removes the cost on hydraulic tests. For in-situ aquifer tests, the HC-system is a valuable new rock mass classification system for preliminary assessment of the degree of permeability in a packed-off interval of a borehole.
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