THE ELECTRICAL RESISTIVITY CHANGES AND VOLUMETRIC STRAIN OF WATER-BEARING CRACKED ROCK SAMPLES UNDER UNIAXIAL COMPRESSION

The axial and transversal electrical resistivity changes in water-bearing, and high temperature baked gabbro rock samples together with their volumetric strain have been measured simultaneously and continuously under uniaxial compression. The measurement shows that the value of resistivity decreases at first before complete water saturation in the stage of non-elastic compression, then it begins to increase in the stage of complete water saturation and elastic compression. Finally the resistivity increases again during the last non-elastic dilatancy stage. According to Archies law, an approximate relationship between the resistivity change and volumetric strain has been obtained through mathematical analysis. Qualitatively, our experimental results are in agreement with it, but not quantitatively. The main result obtained is that the electrical resistivity of water-saturated rock samples increases during the dilatancy stage under uniaxial compression. It may be explained by decrease of water saturation as caused by reopening of the heated cracks.