Research On Acoustic Emission Characteristics Of Backfill With Uniaxial Compression And Splitting Failure Process

In order to study the characteristics of acoustic emission during damage and failure of backfill,This paper haved studied the acoustic emission test of uniaxial compressive and splitting failure of cement grade cemented tailings backfill with the ratio of 1: 4 and 1: 8. Analyzed deformation and failure mode of backfill sample, and received the characteristic law of acoustic emission parameters in the destruction process of backfill sample. On this basis, by calculating and analytical the b value and the associated fractal dimension of acoustic emission parameters, obtained crack initiation and propagation of damage evolution under different stress of backfill sample, and proposed the prediction based while backfill instability failure. Further, By using numerical simulation software RFPA2 D reproduces the failure process backfill sample under uniaxial compression and splitting tensile conditions, described the crack initiation to the whole process instability and failure from the microscopic point of view. Finally, used acoustic emission can rate parameters of backfill defined the damage variable, and established relationship with the backfill injury and parameters of acoustic emission. The main conclusions are as follows:(1)The failure process of backfill which is divided into pore pressure tight crack stage, segment linear elastic stage, plastic yield stage and unstable failure stage. But the plastic yielding stage is very short for splitting failure of backfill, usually presents brittle splitting failure.(2)With the ratio of 1: 4 backfill specimens under uniaxial compression damage mainly characterized hyperbolic shape, "eight" or inverted "eight" shape, but with the ratio of 1: 8 backfill specimens mainly characterized one or several specimens throughout the band splitting, produce localized shear failure plane. Destruction in the form for the split test of backfill mainly throughout the specimen "symmetrical" split along the axis.(3)Uniaxial compressive and splitting failure produced less acoustic emission signals at the early stage of loading, and appeared a lot of acoustic emission signal at the point or near the peak of the stress. Splitting destruction of the backfill sample different from specimens under uniaxial compression is that a lot of acoustic emission signal appeared at the beginning of peak stress point of about 45%, and appeared "flat volatility" period of the acoustic emission signal peak period.(4)The curve will drop while uniaxial compressive and splitting failure of the specimen of backfill or near destruction the b value and fractal dimension of acoustic emission. But the splitting failure specimens fractal dimension of acoustic emission will show a significant "down- up" volatility turning point at the beginning of peak stress point of about 45%-65%. And then the fractal dimension of acoustic emission of fluctuating frequency appeared significantly faster. Means that the specimen would about to destroy.(5)Combined variation law while b values and fractal dimension of acoustic emission and simultaneously decreased significantly accelerated down the oscillation frequency of backfill sample, can be used as a precursor to rupture instability for backfill.(6)RFPA2D numerical simulation reproduced the entire evolution instability from crack initiation to destroy for backfill sample. Compression and splitting failure is initiation micro unit of damage near the center of specimen first, then scattered many micro unit failure, and then the derived into development crack with chaotic expansion, subsequently converted to ordered cr-ack extension, Finally, the formation of a compression test piece or several m-ainoblique crack and cause damage, and splitting sample eventually form macro-scopic crack along the middle to the end and resulted damage in the center of the disc loading axis, showed good agreement comparative laboratory tests.(7)Through acoustic emission can rate define the damage variable under uniaxial compression and splitting tensile failure of backfill, obtained the stress- strain- damage curve and established damage model equations with acoustic emission can rate, analyzed situation between the different strain injury phase.