Failure Mechanisms of Fractured Rock - A Fracture Coalescence Model

Uniaxial compression experiments with a rock-like model material showed that preexisting fractures coalescence in two different modes. If the preexisting fractures overlap coalescence through interconnection of the developing wing cracks; if the preexisting fractures do not overlap coalescences occurs through secondary cracks which occur in addition to and after the wing cracks. the coalescence loads for non-overlapping fractures are lower and thus more critical than for overlapping fractures with otherwise identical geometry. Coalescence through secondary cracks has so far not been observed experimentally. Also, no predictive analysis did exist for either one of the two coalescence modes. Thus, an analytical model for secondary crack coalescence was developed and validated. It was formulated by combining a smeared crack/damage mechanics approach with a strain based failure criterion. 18 refs., 16 figs.