The effect of tensile strength on the stability of rock slopes

The stability of a rock slope is generally considered a function of the shear strength of the rupture surface. In natural slopes the rupture surfaces are often discontinuous and may be composed of fractures and joints separated by blocks of massive rock. In those situations the strength of the rupture surface is composed of three strength components: tensile strength, cohesion and friction. While the effect of the shear strength components, cohesion and friction, on slope stability are well understood, little research has been carried out on the role of tensile strength in rock slope stability.The results from this research show that the tensile strength of the intact blocks that separate fractures is a key parameter in the development of the rupture surface. For toppling slopes, friction and cohesion of the intact rock play a minor role, while the tensile strength play a major role in controlling the stability of the slope. A comparison of conventional discrete element modeling with the modeling methodology developed for this research at all scales investigated shows that the measured deformation patterns, and location of the rupture surface were in better agreement with the simulation results from the proposed methodology. The results indicate that the long-term stability of toppling slopes is likely controlled by the degradation of the tensile strength.The main goal of this thesis is to examine the effect of tensile strength and tensile fracturing on rock slope toppling. Toppling of rock slopes is defined by thin slabs of rock displacing out of the slope, eventually forming a rupture surface. This toppling process involves slip between the thin slabs and tensile rupture across the slabs. A numerical modeling methodology based on a discrete element framework was developed and used to investigate the effect of each strength component (tensile, cohesion, friction) on toppling stability. The methodology, which includes internal flaws in the intact rock, was first evaluated using the results from direct shear tests of discontinuous fractures. The procedure was then applied to centrifuge model tests of a toppling slope. Two case studies of large-scale slopes were also evaluated using the developed modeling methodology.