AN EXPERIMENTAL STUDY ON THE VARIATION OF ROCK RESISTIVITY UNDER TRIAXIALLY DIFFERENT STRESSES

This paper deals with the relation between resistivity change with the form of the loading procedure and strain accumulation rate of a moist saturated sandstone sample, under triaxially different stresses. In the test, the sample was loaded at first by a certain hydrostatic pressure, keeping the minimum principal stress 3 constant, then two types of loading procedures were examined.Type Ⅰ: Loading of the maximum principal stress 1 and the intermediate principal stress2 in three rates, quick, slow and very quick.TypeⅡ: Loading of 1 and 2 in four stress rates, slow, quick, steady and very quick.During the experiment, 1 and 2 were loaded up to the stress level about 80-90% of the failure strength of the rock sample, then unloaded immediately to the initial hydro-static stress level. At the same time, the change of strain rate was limited to the range of 10-6-10-7 per second.The results obtained agree fairly well with the observations in-situ before and after some major earthquakes. They reveal the phenomenon of apparent resistivity variation by stages, before and after an earthquake, probably relating to the manner of accumulation of strain energy, strain rate and energy release in the development of the earthquake source. So the experimental results may provide basis for theoretical explanation for the earth resistivity variation before an earthquake.