This paper presents a new approach to predict both the strengthening effect of a bolting system and the deformation of reinforced rock slopes. This approach is based on a new analytical model which allows one to compute the bolt contribution to the shear strength of a rock joint as well as the associated joint displacement. The main characteristics of this model is the consideration of the interaction of the axial force and the shear force acting in bolts and the consideration of large plastic deformations for the computation of the bolt displacement. For a slope, defined by the height, the dip angle of the discontinuities and the mechanical properties of both the discontinuities and the intact rock, it is shown how to judiciously select the main characteristics of the reinforcement system in order to obtain the required safety factor.
Cet article presente une nouvelle approche pour la determination de I'effet d'un boulonnage systematique sur la stabilite et les deformations des talus rocheux. Ce nouveau modèle analytique permet de calculer la contribution d'une barre à la resistance au cisaillement d'un joint rocheux ainsi que Ie deplacement qui en resulte. Ce modèle prend en compte l'interaction entre l'effort normal et l'effort tranchant mobilises dans la barre ainsi que les grandes deformations plastiques de la barre. Pour un talus defini par sa hauteur, Ie pendage des couches, les caracteristiques mecaniques de la roche intacte et des joints, il est possible de determiner judicieusement les paramètres du boulonnage systematique pour obtenir Ie facteur de securite requis.
Der vorliegende Beitrag stellt eine neuartige Betrachtung zur Vorhersage der Wirkungsweise von passiven Ankern und der Verformungen ankerverstarkter Felsbûschungen vor. Diese Fuβt auf einem neuen Rechenmodell, das den Beitrag des Ankers zur Scherfestigkeit einer Felstrennflache and die dazugehörige Verschiebung anzugeben erlaubt. Dieses Modell beruecksichtigt die Wechselwirkung der Normal- und der Scherkraft im Anker sowie groβe plastische Ankerverformungen. Es wird gezeigt, wie sich fuer eine durch ihre Höhe, die Schichmeigung sowie die mechanischen Kennwerte des Felsens und der Trennflachen definierte Böschung die Kenngröβen einer systematischen Verankerung ermitteln lassen, um einem gewuenschten Sicherheitsbeiwert zu erhalten.
The reinforcement of rock masses by passive rock bolts is nowadays widely used to ensure the stability and to restrain the deformation of rock engineering structures. The mechanical action of the bolt is, however, still difficult to determine, especially for bolts installed in fractured rock masses. As a consequence, there is no unanimously approved method for the design of the reinforcement system. The present study propose a new analytical model for the mechanical behaviour of bolted rock joints subjected to shearing. It allows to compute both the strength and the deformability properties of a bolted rock joint, when the failure mechanism involves sliding displacements along the joints. Only untensioned fully grouted rock bolts are investigated.
A lot of experimental programs were performed in order to describe in a qualitative manner the behaviour of bolted rock joints. Dight (1983), Schubert (1984), Spang (1988), Egger and Zabuski (1991), Ferrero (1993), Pellet (1994) carried out experimental studies on different types of rock material reinforced by various elements. Moreover, several analytical expressions have been developed to predict the behaviour of a bolted rock joint. The simplest of them considers only the axial force acting in the bolt. Dight (1983) proposed an expression to predict the maximum force mobilised in the bolt as well as the associated displacement on the joint. The failure of the bolt is determined by the combination of axial and shear forces, and the displacement is computed taking into account the yielding of the grout. Based on Dight's work, Holmberg (1991) proposed a method which gives a good prediction of the maximum bolt contribution when the bolt is inclined to the joint. Furthermore, Spang and Egger (1990) proposed empirical expressions to compute the maximum bolt contribution and the associated joint displacement. On the same time, some authors (Aydan 1989, Swoboda and Marence 1992, Egger and Pellet 1992) proposed numerical approaches.
