Effect Of Rotation Of The Second Loading Cycle On Kaiser Effect Of Rock Acoustic Emission

For the requirement of Engineering, how to measure the in situ stess precisely hasalways been an important work for the engineers and technologists. The acousticemission method based on the Kaiser Effect of the rock, has aroused generally interestsfor its good economics and a wider application potential. By joints of the efforts of allthe reasearhers, utilizing Acoustic Emission(AE) to mearsure the in situ stress has madea visiable progress in various fields. However, there still are so many key questionsshould be answered. The most basic question is about direction independence, whichmay directly decide the method based on Kaiser Effect credible or not. In addition, thechanging of confining pressures, sampling deviation, the changing of the in situ stressfield while performing underground project and many other situations all may result inthe change of loading direction. So, the influence of Kaiser Effect with a rotation calls afarmore research.The main works carried out and basic conclusions obtained present as follow:①Aresearch on the method to determine Kaiser characteristic point of rock.For the present situation of widely determine Kaiser Effect points just intuitivelyand ignored the significance of the method those can qualify the determination. Inaddition, in this thesis, some research has also been made on the mothods to determinethe Kaiser Effect characterastic points. It presents a comprehensive collection of themost methods of Kaiser Effect （KE） point determination and with a clearly discriobelof their principle. And also with some advices to some details while use these methodand the codes programmed by Matlab to utilize these methods. Moreover, in this thesis,a comparison of clearness of Kaiser Effect point on different acoustic emissioncharaterastic curves and with different stage of pre-load applied has been made.It showsthat:1) For the different acoustic emission charaterastic curves, the clearness of Kaiserpoint goes: accumulation of AE energy> accumulation of AE hits> accumulation of AEevents. On one hand, the Kaiser point on the curve of accumulation of energy；on theother hand it may shows some other mutation points apart from the real Kaiser point, which may clouds the judement. And the curve with accumulation of hits shows to bewith less interference.2) For the different stage of pre-loads,while the pre-loads reach toa specific stage,the clearness of Kaiser points turns to be unclear gradually.②Theoretical analysis Based on the assumption of the Kaiser Effect is a result of the development ofmicro-crack.In this thesis, some theoretical analysis has also been made on the KaiserEffect influence by a load with rotation. In this thesis, an analysis on the changeregulation of critical stress with different angles between stress orientation andmicro-crack has been done. It performed in three cases, for two cases, an ovalmicro-crack with a far-field of tensile and compressive stress in an infite towdimensions by each.And the other is a disk crack with a far-field tensile stress in threedimensions.With the analysis of the change regulation, it indicated that:1) The samplewith the single direction and same type of micro-crack, with a rotation of second cycleof loading, the loads memoried by the characterastic of AE（acoustic emission）curve isjust depend on the rotation.But it does not just memory normal stess of the seconddirection;2) The sample with various directions or multiple type of crack, the KaiserEffect turn to be unclear along with the the rotations from0°to90°;3) The influence onKaiser Effect with a rotation analysis based on theory in case of a disk micro-crack inthree dimensions fitted the experiments result well.③Experimental studyThis thesis has made a research on the case of applying loads on two differentdirections by turns to observe the effects of direction change on Kaiser Effect. Testswere performed in two different ways. One of the tests was performed in Brazilian diskloaded in two cycles with rotation of5°,15°,30°,45°,60°and90°. As to avoid theshortcomings of general epxperimentl method, another test was performed intwelve-sided shape, eight-sided shape, hexagon and square samples, with which toobserve the effects with rotation of30°,45°,60°and90°.The experiment shows that:1)the accumulation of AE energy curves of the second direction has a memory of theloads of first direction in a big range of rotation angles.2) But with the angles bettwencycles loads change from5°to90°, the Kaiser Effect turns to be not clear。For90°, itseems to most likely with no pre-loads.3) By the different rotations, the ratio betweenthe the load remembered by the characterastic curve of second directon and the loadapplied on the first direction was divergent.And with no obvious appearance to show theratio is monotonous.with the change of rotaions.