Experimental Study On The Effect Of Triaxial Stress State On Rock Kaiser Effect

It is a convenience and cheap way to measured geostress by using Kaiser effect by using rock samples. However, there are still some basic theoretical problems unresolved, and one of them is the determination the stress values to be measured corresponding to the points of Kaiser effect under triaxial compression.As we know, actual rock mass is always under the state of stress of triaxial compression, which is completely different from that under uniaxial condition in laboratory. Therefore, the results from the uniaxial compression can hardly keep consistante with that of actual condition. However, most of the investigations and applications are performed in uniaxial conditions.The control system composed of rock sample, triaxial testing machine and acoustic emission detector, by using granite samples of Changzhou, Hubei province of China. Confining stress of 5MPa, 10MPa,15MPa,20MPa,30MPa, are applied in the tests. The figures of AE counts-time-stress curves, cumulative energe-time-stress curves, etc., are obtained. The main conclusions are:(1) Under the conditions of uniaxial compression, acoustic emission activity is not very much in the early stage of loading, and it is usually acceleration with the increase of loading when the stress value arrives 30 to 90% of the strength value, while acoustic emission growths steady after additive confining pressure applied;(2) If the additive confining pressure is same, the cumulative number of acoustic emission is similar under uniaxial compression, but with the additive confining pressure increases, the cumulative number of acoustic emission of acoustic emission is reduced;(3) Kaiser effect exists for the tested granite samples under the conditions of unaxial compression after additive confining pressure been applied, and such a phenomenon appears only when the applied stress keeps in the arrange of 30% to 90% of rock failure strength;(4) With the raising of the additive confining pressure, the ratio between the stress that the memory of Kaiser effect with the maximum stress of loading earlier descends;(5) The smaller the ratio between additive confining pressure and axial compression pressure gets, the better result of the Kaiser effect memory. When the ratio is greater than 1, Kaiser effect can hardly be detected.