| The relative quiet period of rock acoustic emission before the rupture is generally considered as an important precursory characteristics of rock rupture,revealing the mechanism of rock acoustic emission relatively quiet period has important theory value and practical significance.In order to understand the relationship between the acoustic emission parameter or the relative quiet period of rock acoustic emission and the particle size,analysis relatively quiet period features quantitatively,selecting high purity quartz sand of four kinds of particle size(0.08-0.16 mm,0.315?0.63 mm,1?1.25 mm and 1.5?2 mm)as aggregates and cement as cementing agent to make rock simulation materials(rock-like material).In this paper,uniaxial compression-acoustic emission tests and numerical simulations of rock-like materials were conducted to investigate and discuss acoustic emission parameters and the relationship between relative quiet period and particle size.The main conclusions are as follows:(1)The stress-strain curves of all particle size specimens are smooth,showing strong ductility,and the large-diameter specimens are more obvious;their deformation characteristics also show large differences with particle size changes.Among the four particle sizes,the elastic modulus and uniaxial compressive strength of the specimens with diameters of 0.315?0.63mm are the largest;the specimens within 0.315?2mm,the elastic modulus and the uniaxial compressive strength are smaller with increasing particle diameters.(2)The evolution rule of the basic acoustic emission parameters of the four particle size specimens is that the larger the particle size is,the later the acoustic emission becomes active.The distribution of amplitude fractal of the acoustic emission of the four particle size specimens is basically consistent with that of the energy fractal.There is a general downward trend In the process of compression of the test specimen.The critical discontinuity point of specimens destruction is basically within the stress level of 60%-90%.In the initial compaction stage,the r-value(?N/?E)of large-diameter specimens with particle sizes of 1?1.25mm and 1.5?2mm decrease more obvious than those with smaller particle sizes of 0.08?0.16mm and 0.315?0.63mm.At the peak stress point,there is a small sudden drop in the r-value of the large particle size specimen.(3)For the particle size is between 0,08 and 2mm,the larger the particle size,the more widespread the relative quiet period of acoustic emission of the rock-like material is.Among them,the particle size is in the range of 1?2mm,and the larger the particle size,the longer the relative quiet period.Compared with relatively quiet period,the low frequency range before in acoustic emission relatively quiet period is narrow,and no low frequency appeared.After the relatively quiet period,the sample be completely destroyed,and the low frequency signal arised in a significantly lower stress.110?120kHz is the sensitive frequency band of the cracked acoustic emission signal of the rock material.The occurrence rate of the frequency band is significantly reduced in the relative calm period of the acoustic emission of rock failure.(4)Large-diameter specimens have lager range frequencies of acoustic emission than small-diameter specimens,and the highest frequency values are higher;at the peak stress point,the lower frequency and highest frequency coexist in four types of rock-like materials.(5)In the numerical simulation,the cumulative number of microcracks at the peak stress point decreases with particle size bigger.For specimens with a particle size of 1.5?2mm,almost no microcracks occur at 90.37%?97.14%of peak stress,which is consistent with the phenomenon of relative quiet period of acoustic emission. |
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