A deformation model of rock is developed based on the analysis of microcracks under compression. The relations between stresses, crack growth, and the induced deformation are established. The post-failure stage is simulated by considering a shear failure band formed due to the coalescence of microcracks. The nonlinear behaviour and the hysteresis are captured by the model. Simulations are compared with experimental data. The effects of material and crack parameters on deformation are examined using the model.
Un modèle de deformation des roches, base sur I'analyse des micro-fissures apparaissant en compression, est developpe. Les relations liant les contraintes, la croissance des fissures et la deformation induite sont etablies. L'etat de post-rupture est simule en considerant la formation d'une bande de cisaillement due à la coalescence de micro-fissures. Le comportement non-lineaire et le phenomène d'hysteresis sont reproduits par le modèle. Les simulations sont comparees avec des donnees experimentales. L'influence, sur la deformation, de la nature du materiau et des paramètres de fissures, est examinee à I'aide du modèle.
Es wurde ein Deformationsmodell von Gestein entwickelt, das auf der Analyse von Mikrorissen unter Kompression beruht. Die Beziehungen zwischen Spannung, Risswachstum und der durch Reissen hervorgerufenen Verformung sind aufgestellt. Die Phase nach dem Bruch wird unter Einbeziehumg einer Schubbruchzone simuliert, die auf Grund der Verbindung von Mikrorissen geformt ist. Das nichtlineare Verhalten und die Hysterese werden von dem Modell erfasst. Die Simulationen sind mit den experimentellen Daten verglichen. Die Auswirkungen von Material- und Bruchparametem auf die Verformung sind unter Anwendung des Modells untersucht worden.
The failure of intact rock is not only a basic theoretical problem on rock mechanics, but also a problem of engineering practice. Spalling, which is the most common failure mode in mine pillars, is one of the examples of the intact rock failure. The spalling failure is most likely to start as extension strain fracturing through intact rock. It includes the processes of both crack initiation and progressive failure. These features have seldom been included in computer codes to date (Sjoberg 1992). From both theoretical and practical points of view, further study on the failure of intact rock is needed. Rock is composed of different minerals. These minerals have different physical and mechanical properties, which could initiate failure in stress fields. On the other hand, it also contains a great number of microcracks and voids. The behaviour of microcracks is crucial to the failure of rock. Microcracking is believed to be the main mechanism for the nonlinear deformation of rock. The behaviour of microcracks should be included in constitutive laws for rock. Experiments have demonstrated that cracks propagate towards the direction, of the major principal stress under compression (Horii and Nemat-Nasser 1986; Kranz 1979). Axial splitting is the basic mechanism of failure developed in brittle rocks before the load reaches its peak. One of the most common final failure modes of rock under compression is the formation of shear faults. Microscopically, this final shear failure mode is also associated with rnicrocracking processes (Gramberg 1989). Constitutive models have been developed by considering the axial growth of microcracks (Costin 1985; Moss and Gupta 1982; Kemeny and Cook 1987; Nemat-Nasser and Obata 1988). The nonlinear behaviour caused by the fracture of microcracks is captured in the models, but not yet the hysteresis. Furthermore, the post-peak behaviour has not been studied in most of the micromechanical models to date. This study attempts to advance the micromechanical modelling of the compressive fracture of brittle rocks. The constitutive model introduced in this paper includes both the prepeak and the post-peak behaviour.