Modelling the Kaiser effect and deformation rate analysis in sandstone using the discrete element method

Non-destructive methods for rock in-situ stress estimation have been extensively investigated in recent years. Such techniques as deformation rate analysis and the acoustic emission method, which are based on 'rock memory' recovery utilising the Kaiser effect, have become popular among many practitioners. The physical nature of this phenomenon has not however been universally established. In this study the primary cause of the Kaiser effect, the interaction of microcracks, was investigated. The numerical modelling package PFC2D was employed for creation of a synthetic cored specimen and simulation of uniaxial compression tests. The ability of the numerical model to reproduce the Kaiser effect and the deformation rate analysis phenomenon was confirmed, and a direct comparison was made between laboratory and numerical observations. The link between the Kaiser effect/deformation rate analysis and development of microcracks was established. The realistic behaviour of the numerical model can be used for exploration of other mechanical properties of rocks and also to further study the characteristics of the deformation rate analysis curve. The results of the modelling work may provide assistance for a more accurate interpretation of deformation rate analysis curves. (C) 2003 Elsevier Ltd. All rights reserved.