A plasticity-based interface model for describing the mechanical behavior of rock joints and fractures is presented. The isoparametric formulation of the zero thickness interface element and the implementation procedure of the constitutive laws into a standard non-linear numerical code is briefly described. A failure criterion is proposed and is shown to fit well the direct shear test data obtained for sawtooth concrete-rock interfaces. The predictive performance of the constitutive model is assessed and typical results are presented in this paper.
Cette communication decrit un modèle base sur la theorie de la plasticite et representant le comportement mecanique des joints et des fractures. La formulation isoparametrique d'un element interface d'epaisseur nulle, et l'introduction de lois de comportement dans le code numerique non-lineaire est decrit brievement. Une loi de rupture est proposee et est jugee valable basee sur les resultats obtenus lors d'essais de cisaillement direct sur des echantillons contenant un interface irregulier mortier/roche. Les prediction du modèle sont evaluees et un nombre de resultats sont indues dans cette communication.
Ein auf Plastizitat aufbauendes Kontakfllachenmodel, das mechanische Verhalten von Gesteinsklueften und Bruechen beschreibt, wird vorgestellt. Die isoparametrische Formulierung des "Null-Dicke-Kontaktflacheuenements" und die Prozedur zur Einfűgung der konstitutiven Gesetze in einen standardisierten nicht-linearen numerischen Code wird kurz beschrieben. Ein Bruch-Kriterium wird vorgestellt und es wird gezeigt, dass dieses gut zu den Daten aus dem Scherungstest passt, welcher fűr Sagezahn Beton- Gesteinskontaktflachen durchgefűhrt wurde. Die Vorhersagekraft des Models wird erarbeitet und typische Ergebnisse werden in der Verőffentlichung vorgestellt.
It is widely accepted that the presence of fractures and discontinuities governs the strength and load-deformation behavior of rock mass. The response of an -interface to shear loading depends to a large extent on its surface properties, as well as the boundary conditions that are applied across its surface, either near or far away from the interface itself. The mechanism of shearing two rough surfaces which are initially in contact is still poorly- understood. Solutions are available for elastic bodies in contact that have simple geometries for some classical problems. However, for discontinuous and fractured rock mass, it is difficult to apply the mathematical theories developed for classical contact problems and thus, numerical techniques such as finite element method are frequently used. In this paper, a constitutive model for rock joints is formulated in analogy to the theory of plasticity. The mechanism of bonding, debonding and frictional slip which characterize the interface behavior is presented. At the outset, various techniques for modeling rock joints are reviewed. The implementation of the newly developed interface model into a non-linear finite elements code is discussed. Various step involved in the numerical integration of the constitutive equations are described. The predictive capabilities of the proposed constitutive theory are evaluated.
The complex mechanism of frictional behavior of discontinuities and interfaces can be attributed partly to the contacting materials and to the presence of infilled materials, if any, within the interface. In addition, on the microstructural level the problem is compounded due to the presence of voids and asperities within a very thin layer. The main factors upon which the strength of an interface under combined normal and shear loading depends on mineral to mineral surface friction, magnitude of the normal stress, shear strength of the weaker material in contact for very rough interfaces and, asperity angle representing the roughness. The friction and stress dilatancy theories have been major research topics for many decades.