Influence of tensile loading direction on accuracy of determining Kaiser effect point

The Kaiser effect is caused by the elastic waves generated by the crack propagation. Based on this common understanding and the theory of fracture mechanism, the influence of the loading direction on the Kaiser effect is discussed when the far field stress is the tensile one. The relationship between the critical stress of the crack propagation for I + II mixed mode in plane, the value of Felicity ratio (FR) and the rotational angle of loading are studied. The results show that the loading direction has important influence on whether the Kaiser effect can correctly reproduce the information on the peak stresses of the rock experienced in the past. If the loading in the first cycle is perpendicular to the crack and the rotational angle changes from 0° to 90°, the critical stress of the crack propagation and the FR value will increase with the rotational angle. When the rotational angle varies between 0° to 20°, the FR will value the changes between 1 to 1.1, and the “Memory” of the Kaiser effect is more accurate, while the stress memorized by rock in the second direction is not the normal one according to that direction. When the rotational angle is 90°, both the critical stress of the crack propagation and the FR value increase to infinite, and the crack isn’t able to propagate in its crack surface. Hence it results in complete disappearance of the Kaiser effect. They are consistent with those of some other researchers. Therefore it can be concluded that the crack propagation is the main cause of the Kaiser effect in this kind of split tests. It can also explain why the Kaiser effect becomes more and more inapparent with the increasing rotation angle.