Initial Assessment on Hydraulic Conductivity of Rock Mass and its Size Effect Using Drilling Data

Predicting hydraulic conductivity and characterizing its size effect in jointed rock masses is fundamental to various geoscience and engineering disciplines. A new empirical method, using drilling data, is established to predict the hydraulic conductivity of a rock mass in the scanline direction. The effect of the scanline unit length on the distribution characteristics of hydraulic conductivity for boreholes in jointed rock masses is studied. In addition, the scanline length of boreholes was used to study the size effect of hydraulic conductivity of jointed rock masses, and a new model was proposed to determine the size effect of hydraulic conductivity. A mathematical method for representative volume element (RVE) determination was proposed based on the proposed size effect model of hydraulic conductivity. Some packer tests were conducted to validate the developed method for predicting hydraulic conductivity. The results show that (a) the predicted hydraulic conductivities are close to those determined from the packer tests; (b) the scanline unit lengths influence the distribution characteristics of hydraulic conductivity; (c) a large but fluctuating increase in hydraulic conductivity with increasing scanline length, and the fluctuation decreases with fewer fractures and joints; (d) the mathematical method for predicting RVE and K_RVE is effective to make an initial evaluation on jointed rock masses with high fracture frequency.