Electrical Measurement of Rock Deformation and Rock Fracture by Blasting

Abstract

The methods that are commonly used in civil engineering for the purposes of locating sites for construction of dams and reservoirs, of locating ground water, of determining the thickness of weathering layers, of locating fault zones, of locating sites for tunnel construction, and for keeping precise well logs, are by electrical prospecting.
In the present paper, a new electrical method to measure the deformation and the fracture of rocks caused in consequence of the blasting, is proposed and explained as experimented in the cases of the Nagano Dam, Electric Power Development Co., Ltd. (Figs. 3, 4 and 5), the Kiso Tunnel, Kansai Electric Power Co., Ltd. (Figs. 6 and 7) and the Kubiki Tunnel, Japanese National Railways (Figs. from 8 to 13).
In blasting high pressure compressive waves are produced which propagate themselves through the earth structure surrounding the blasting point. By these waves deformation and fracture are generated in the earth structure and so variation of earth resistivity takes place. There are two kinds of the variation of the resistivity. One of these, known as the seismic electric effect, is the variation generated by the deformation only during the presence of the waves. The other one is the variation generated by the fracture which does not return to the initial earth structural condition.
The variation of the resistivity of the first kind is shown in Fig. 4. The variation of the resistivity of the second kind is shown in Fig. 5, 6 and 7.
The relations between the resistivity and porosity are shown in Eqs. (2) and (3).
This electrical method is valid in investigating the blasting effects in civil engineering.