A PRELIMINARY REPORT ON AN EXPERIMENT OF MEASURING ROCK STRAIN BY THE METHOD OF APPARENT RESISTIVITY IN A MINE TUNNEL
CHEN FENG LIAO FA-TIAN TANG HSIEN-MIN(Worker-peasant-soldier students in the Department of Geophysics, Peking University)
The purpose of this experiment is to show the relation between electrical resis-tivity and strain of rocks under stress, in an attempt to indicate that whether or not resistivity variations can be used as precursory phenomena before earthquake occurrences.The experiment was done in a mine tunnel, more than 100 meters under ground. Four-elctrode arrangement was employed to measure the apparent resistivity, using dry cells of maximum voltage 13.5 volts as current source. Maximum observational mean square error amounts to 1-2%. At five points on the rock surface, we pasted resistivity strain gauges, for measuring the magnitude, direction of the principal strain in the rocks so as to compare the observations with the maximum apparent resistivity values. The maximum reading error of the strain gauge does not exceed 3-4με. During the experimentation, serious electrode polarization phenomena was taken into consideration.Preliminary results of the experiment show that the general tendency of ap-parent resistivity and stress of the rocks essentially vary in unison. It is therefore expected that the appareant resistivity method can be used to measure rock strain. Several earthquakes occurred in the Nanping area of the Szechuan Province in 1973, were used as examples to show certain correlations.Some questions concerning the experiment were also discussed in this paper.