Experimental Study On The Effects Of Different Loading Paths On The Kaiser Effect Of Rock

In recent years,the method of rock Kaiser effect measuring the in-situ stress has been widely studied and used,which is convenient and economical advantages.However,there are still some unresolved technical problems at present,one of which is that when the core is drilled to measure the in-situ stress by the indoor test of Kaiser effect,the axial direction of the drilled core and the principal direction of the field principal stress is inconsistent(Ie,the initial loading direction does not coincide with the subsequent loading direction),the indoor test of Kaiser effect can prove Kaiser effect whether or not exist or get the correct result.In this paper,using granite done indoor test,we study the influence of the angle that is between the initial loading direction and the subsequent loading direction for Kaiser effect under the condition of uniaxial loading.The influence of the angle size is the exist of Kaiser effect and the judgment of the Kaiser point.At the same time,the influence of different preload paths on the Kaiser effect are also studied under triaxial loading.The main conclusions are as follows:1.Under the condition that the initial loading stress is at a low stress level well below the 30%strength of the specimen,the Kaiser effect is not significant when the acoustic emission signal is small.In this case,the average value of the corresponding stress level as the Kaiser point is more accurate when the energy count and the ringing count begin to continued increase for the first time.2.Under the condition that the initial loading stress reaches a higher stress level(close to 65%of the sample strength),when the second loading stress has not reached the previous maximum stress and the acoustic emission signal becomes active,the cumulative energy count and the cumulative ringing curve after the first curvature increases the corresponding point of the corresponding stress level as the Kaiser point,the error is small.3.For the different loading path test under the triaxial preloading,they could be summarized:? Under the triaxial preloading path that is loading the axial pressure before loading the confining pressure;The corresponding stress on the Kaiser point of the second uniaxial loading is good correspondence for the preloaded axial pressure.That is,the confining pressure has no effect on the Kaiser effect.?.Under the triaxial preloading path that is loading the confining pressure before loading the axial pressure;The Kaiser effect does not appear.?.Under the triaxial preloading path that is loading the axial pressure and the confining pressure loading at the same time;The Kaiser effect does not appear.4.For the 15 ° and 20 ° changes in the subsequent loading direction under uniaxial test conditions,it was found that a significant Kaiser effect was observed at the second loading,The corresponding stress on the Kaiser point of the second uniaxial loading is smaller than the preloaded axial pressure.And the values of FR is 0.76 and 0.71.