Characteristics Of Phyllite Peak Stress Around Loading And Unloading And Acoustic Emission

Stability of the engineering rock mass has always been the important topic of undergroundand slope of rock engineering. Lots of theoretical and experimental study in this field has beenmade at home and abroad. Rock acoustic emission (AE) is one of the important monitoring waysof rock mass failure. But now there is quite rare quantitative studies of phyllite rock AE of thewhole process under uniaxial loading. Uniaxial compression of AE test of phyllite was carried outto obtain AE characteristics in the phase of loading-unloading and before and after peak stress.Two parameters named ration value ie. ΣN/ΣE and ib value are adopted in this paper. First, typesof failure and its corresponding AE characteristics were analyzed. And distribution regularities ofration value and ib value during loading and unloading were studied. Furthermore characteristicsof the two parameters were also analyzed. Main conclusions of this paper are as follows:(1) Destruction type and AE characteristics of phyllite can be divided into three categories:first, with a destruction in the form of trapezoidal, the AE continued before and after the peakvalue; second, has a trapezoidal destruction (also with schistosity trends), with a period of quietof AE before and after the peak; third, has a schistosity destruction, the majority of AE continuedbefore and after the peak. Under the axial compressive stress, transverse tensile stress appears dueto the Poisson effect, resulting in a special schistosity failure mode of phyllite, smooth schistositynearly parallel to the rock is flaky.Quiet period of AE will not appear to the layered destructivephyllite along to the schistosity. Therefore, through on-site observation and judgment, fieldprediction of the stability can be guided.(2) In the loading process, as the increasing stress of phyllite, ΣN/ΣE value will graduallydecrease and approach zero. Meanwhile, in the unloading process, due to the slowly decreasingof stress, ΣN/ΣE value gradually increases from zero. So, the∑N/∑E value of phyllite under alow stress level is considered to be a larger one, which shows that there is a large number oflow-energy events to be happening; while under high stress conditions, the ΣN/ΣE value is small,which means that a small number of high-energy events is happening.(3) From the initial loading to the completely destruction of phyllite, the relationship of AEΣN/ΣE value and time is in a "saddle" shape, before and after the peak stress,ΣN/ΣE value isvery small comparing to the beginning and the end of loading, it is in the bottom of the “saddle”shape, this illustrates that the ΣN/ΣE value of phyllite is very small both in the brink ofdestruction and in the destruction stage.(4) Before the peak stress, AE ib value of the phyllite decreases linearly, while after the peakvalue, the ib value increases and gradually becomes stable, which shows that peak point is aninflection point of the ib value. Therefore, if ib value of the phyllite reduces linearly at one stage, this might be a prediction of its destruction.（5）With the combination of ΣN/ΣE value and ib value, the whole destruction process ofphyllite can be described, and the peak stress value can be identified.