DEFORMATION OF BRITTLE ROCKS UNDER COMPRESSION - WITH PARTICULAR REFERENCE TO MICROCRACKS

A constitutive model for brittle rocks has been developed based on the analysis of microcracks. The macroscopic deformation of a rock is dec omposed into three components: response of the rock matrix, closure of open cracks and deformation due to the fracture of microcracks. The m ain contribution of this approach is the prediction of macroscopic def ormation induced by microcracking. The basic model units are sliding c racks. Wing cracks are initiated at tips of sliding cracks and propaga ted in the major loading direction. The relationships between the comp ressive stress, the length of the growing crack and deformation due to the fracture of cracks are established. A deformation solution to an elliptic crack is employed to describe the closure effect of an open c rack under compression. The total deformation caused by the closure an d fracture of cracks is obtained by the sum of the components of indiv idual cracks. In this model, the nonlinear behaviour of deformation re sults either from the closure of open cracks at low stress levels, or from the fracture of microcracks at high stress levels. Hysteresis is captured under cyclic loading. Comparisons of the model simulations wi th experimental data are presented and show good agreement in the pref ailure stage.