A Rock Mass Classification Scheme for Estimating Hydraulic Conductivity of Fractured Rocks

Abstract

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 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.