The electrical resistivity prospecting is becoming very useful for ground investigation,. because new computer methods have been developed and detailed electric resistivity distribution in ground can be indicated However, characterizations of resistivity for rock mass are not clarified, and it is not sufficiently understood that the measured resistivity values can indicate conditions of rock mass. In this paper, using 17 types of intact rock specimens and 2 types of rock specimens with single joint, the resistivity of these specimens are measured in the laboratory. From these measured data, the relation between resistivity of the rock specimens, saturation, porosity and aperture of discontinuity are discussed. Furthermore, these results obtained by between tests are applied to rock mass assessment in a tunnel.
The resistivity value of rocks cover a very wide range, from around Ωm for shale to around 106 Ωm for fresh igneous rocks, and it is not unusual for rock in the same faces and same class to show variations in resistivity value of around an order of magnitude. For this reason quantitative assessment of geology from only the resistivity value of the rock is generally considered to be difficult. However, since the resistivity of a rock reflects small differences in its degree of alteration and its percentage water content, the distribution of resistivity values is useful information concerning soil properties and rock mass state). In order to assess rock masses using the results of electrical resistivity prospecting, the relationship of the electrical resistivity of the rock mass with the resistivity value for pore water or with saturation must be understood, as must relationships such as that between electrical resistivity for different types of rock and their mechanics, and the relationship between electrical resistivity and mechanics for weathered or fractured rocks.
