Experimental Study Of AE In Rocks

The aim of this work is, using the experimental Acoustic Emission (AE) technique, to study the effect of stress on rock fracture, the changes of some values before rock failure and the influence of cracking in rock on fracture.It is found that cyclic loading at high differential stress level will lead to thedecrease of Felicity Ratio, and the value max can be decreased by some crack systems in specimen. There is still a lot of AE during unloading at high differential stress level, which implies that the deformation is dominated by fracturing at low differential stress level, and the deformation by frictional sliding increases greatly at high differential stress level.Before rock failure, it is found that AE distributed densely, and the coming fracture will occur in the density center of high magnitude events, and AE ratio of frequency grows greatly. These precursors can be presented by the change of b value, A T value and the contour of V value.Prefab crack systems in the specimen will affect the fractures hi rocks. Barrier cracks cannot stop the extending of a fracture, and the strength of the sample is reduced by almost one magnitude because of the existing barrier cracks. There are great differences of AE distribution between specimens with non-penetrate crack and specimens with penetrate crack. As for penetrate crack, AE occurs near the two end of the crack, and for non-penetrate crack,crack, AE occurs near the two end of the crack, and for non-penetrate crack, AE occurs near the front edge of crack, which can be explained well by the theory of 3-D fracture; AE distribution near the outer part of collinear crack is similar with that of the end of penetrate crack, and inner part of collinear cracks will run-through with high loads.