Experimental Study On The Loading Direction Changes Of Kaiser Effect

Primary rock stress is very important to Mining Engineering and Geotechnical Engineering. Nowadays,the measurement methods of primary rock stress can not get a reliable result with lower cost. Kaiser effect of acoustic emission method opens up a new way for measuring primary rock stress. There are still some problems have not been resolved although this method has many advantages. The effect of angles variation to Kaiser Effect will determine the reliability of the measurement results directly.Aiming at this point,uniaxial compression tests and Brazilian tests were carried out with Fujian granite and Gaoligongshan granite. Four prism specimens? six prism specimens and eight prism specimens were made in uniaxial compression tests. we used large diameter and thin disks in Brazilian tests. The effect of rotation of principal axes to Kaiser effect was studied. Bulk density was measured. We got elastic modulus and poisson ratio by stress-strain curves. Time-stress(cumulative energy) curves, time-stress (cumulative ringing) curves and time-stress (AE counts) curves were drawed. The main results are as follows.(1) Time-stress(cumulative energy) curves are better than time-stress(cumulative ringing)curves which in turn better than time-stress(AE counts)curves in the judgment of Kaiser point.(2)Kaiser effect exists between33.17%of strength and83.5%of strength in uniaxial compression.It is between15%of strength77.2%of strength.This result is inconsistent with30%of strength to80%of strength in some literatures.(3)When loading direction changed45°,60°or90°in uniaxial compression,Kaiser effect is not existent any more.(4) When loading direction changed0°,5°,10°,15°20°,30°in Brazilian tests,Kaiser effect is existent in some samples. But memory effect is poor at20°and30°.(5)In case of no load keeping,Kaiser effect has no periodic multiple times in stepwise cyclic loading of uniaxial compression and Brazilian tests.(6)The number of acoustic emission events of Brazilian tests is less than uniaxial compression.(7) AE increases faster until20%of strength in initial loading in uniaxial compression tests. AE grows steady in Brazilian tests.(8) Rock sound acceleration point appares at84.47%of strength in uniaxial compression. AE grows stopped from94.71%to all of strength in uniaxial compression tests. Rock sound acceleration point appares at all of strength in Brazilian tests. It damage suddenly.