Estimation of hydraulic conductivity in a clean jointed rock mass by using electrical conductivity

Abstract

The hydraulic conductivity of the rock mass is a significant parameter in geotechnical engineering, because the fluid flow in a rock mass can cause serious damages to rock-based underground, rock mountains and underground structures, such as tunnels and underground storage reservoirs. However, it is very hard to estimate the hydraulic flow in a rock mass, because it can be affected by the complex geometry of discontinuities or fractures. This study focuses on the analogies between the hydraulic flow and the electrical current flow which can be represented as the hydraulic conductivity and electrical conductivity. Both the hydraulic conductivity and the electrical conductivity of the fluid basically originate from the same physical configurations of the rock mass. Thus, the prediction on the hydraulic conductivity of the rock mass is much easier if it is accompanied with geophysical exploration methods such as electrical conductivity measurements. The goal of this study is to establish an easy method for theoretically estimating the hydraulic conductivity of the rock mass with electrical conductivity measurements. To establish the theoretical relationship between rock mass hydraulic conductivity and electrical conductivity, each hydraulic and electrical conductivities of an intact rock and a fracture are examined. The rock mass consists of the intact rock and fracture, therefore the governing equation of rock mass hydraulic conductivity can be made into a function of intact rock and fracture hydraulic conductivity. The hydraulic conductivity of the rock mass is theoretically correlated to the electrical conductivity. The derived equation can be divided into two parts. The first part is about the intact rock properties such as intact rock electrical conductivity and intact rock porosity and the second part is about the fracture characteristics such as aperture, spacing and rock mass electrical conductivity. Finally, the derived equations are verified through 2 se...