Study On The Characteristics Of Acoustic Emission During The Course Of Post-peak Deformation And Failure Of Rock Specimen Under Loading And Unloading Testing

Acoustic emission occurs certainly for rock mass fracturing. Acoustic emission is a kind of meter phenomenon of initiation and propagation of rock cracks to rock failure and it has important indication action in the process of mine geological disasters. At present, research on rock acoustic emission is mainly concentrated in the rock uniaxial experiments, conventional triaxial in pre-peak test, etc., but the research on acoustic emission characteristics of rock breaking into the post-peak phase is less. In practical engineering, however, rock mass around the mining working face experienced many tectonic reconstructions are in the state of failure and equilibrium. From the view of engineering, this state is similar to the indoor test residual strength stage after rock peak. In addition, the mechanical behavior in process of digging is a loading-unloading process. Therefore, it is necessary to carry out experimental study on the acoustic emission characteristics of the post-peak rock under the condition of loading-unloading in different confining pressure and the experiment is great significance on the analysis of the confining pressure stability and in prevention of mine geological disasters.This article analysis the acoustic emission characteristics of rock specimens in the progress of loading-unloading confining pressure in the post-peak under different confining pressure state. This paper focuses on the relation between mechanical properties of rock and acoustic emission characteristics under loading-unloading confining pressure in the post-peak. The experiment is designed to establish theoretical basis for mine geological disaster forecast analysis based on the acoustic emission characteristics after post-peak. The main research contents and results of this paper are as follows:(1)When the crack initiation strength of the specimen can be achieved, it will appear relatively more acoustic emission phenomenon in the process of acoustic emission test during rock deformation and failure based on conventional triaxial compression. But before the crack initiation strength, the acoustic emission phenomenon is relatively less. When the damage strength of the specimen can be achieved, the acoustic emission phenomenon began to be more active. Before the peak strength, it doesn’t appear any acoustic emission phenomenon and it means that this specimen will impend destruction. When the specimen achieves residual strength, the acoustic emission phenomenon is a relative reduction and the the cumulative ringing count of acoustic emission trends to fall and the curve slope is close to zero.(2)In the process of directly unloading confining pressure after the rock sample in the residual phase, acoustic emission happens less before unloading confining pressure shows up(that is during the residual phase). But after that happens for a while,acoustic emission intends to be more active with a huge increase on its ringing counts and energy. Besides that during this process, the more confining pressure decreases, the more signals will release form test specimen,the bigger the slope of curve for accumulating ringing counts will be.(3)With the increase of confining pressure, mechanical parameters,such as damage strength σcd, peak strength, and acoustic emission parameter, such as amplitude, maximum ringing count, counting rate of energy, have the trend of increase. And the higher the confining pressure, the greater the energy stored within the specimens and the more energy released in the process of unloading confining pressure.(4)For loading-unloading confining pressure tests in conventional triaxial residual phase, it is similar acoustic emission characteristics in the process of loading and unloading in the cyclic loading-unloading test whatever in load shedding and complete loading test.(5)Starting to proceed confining pressure at post peak loading and unloading test under the different initial confining pressure, we can find similarity between rock specimen stress curve at post peak and strain curve.From beginning of the confining pressure to the end that the confining pressure recovers to its primary status, the stress-strain curve is with similar shape with a trapezoid and the residual strength of the rock specimen changes in a analogous pattern, that is, 5MPa is decreased for one time,the residual strength of the rock specimen will decline along with that. The more times the confining pressure is unloaded, the more variation of the residual strength will be.(6)Before unloading the confining pressure,signals released during the residual phase under the initial confining pressure are more than before and the energy emitted is also more powerful.Every time when the test starts to unload the confining pressure, large amounts of acoustic emission signals will show up and energy from acoustic emission will be stronger than that emitted from the residual strength for last phase.Besides that, accumulating ringing counts rockets to a higher level, the curve slope between accumulating ringing counts curve and time increases. However, with the number of unloading rising,the acoustic emission signals emitted from sample specimen and the its energy decreases, accordingly, received accumulating ringing counts and its slope decline,which happens with the same situation as the size of the amplitude range as well as the energy from that show us.(7)During the process of recovering the confining pressure to its initial status, within the primary increase of confining pressure, the received acoustic emission signals are stronger and the curve slope of the accumulating ringing counts correspondingly increases. But increase axial stress after make confining pressure recover to its primary value and keep it stable, at the initial phase,acoustic emission happens less while with continual increase of the axial stress, it shows up frequently. We can take usage of the acoustic emission to measure friction between rock fracture surfaces. When it reaches residual phase, acoustic emission signals will be less and the curve slope of the accumulating ringing counts will be smaller with a slower growth speed.