A modified single plane of weakness theory for the failure of highly stratified rocks

The basic assumption on the cause of anisotropic body failure of rocks is due to either fracture of bedding planes or the fracture of rock matrix and two distinct criteria should be used for the two fracture modes. The most popular of these criteria is known as `the single plane weakness theory'. A modified version of this theory is proposed. The modified criterion is tested against experimental data of a strongly bedded rocks (schist) and compared with the original criterion.; Various failure criteria for anisotropic materials have been proposed. However, according to the assumptions and techniques used in each one, it appears possible to classify these criteria into three groups: mathematical continuous criteria, empirical continuous models and discontinuous weakness plane theories. A tentative classification and detailed comparison of some commonly used criteria have been proposed by Duveau et al. [3]. For highly stratified rocks, it was seen that the 'discontinuous weakness plane theories' generally provide better predictions than the other kinds of criteria. Indeed, in these rocks, the emphasis is put on the description of physical mechanisms included in the failure process. The basic assumption is that the failure of the anisotropic body is due to either the fracture of bedding planes or the fracture of rock matrix and two distinct criteria should be used for the two fracture modes. The most popular of them is known as 'the single plane of weakness theory' proposed by Jaeger [6]. In this theory, the classic Mohr-Coulomb criterion is used to describe the failure of both the bedding planes and rock matrix, but using two different sets of material constants. Good results can be obtained from this criterion for slight stratified rocks. However, for highly stratified materials, the predictions obtained are often not satisfactory. The main explanation is that in such rocks, the bedding planes behave closely like rock joints and the Mohr-Coulomb criterion is not suitable to model the failure of such discontinuities. The purpose of the paper is to propose a modified version of Jaeger's theory. The modified criterion will be tested against experimental data of a strongly bedded rock (schist) and compared with the original Jaeger's criterion.