The importance of step-path failure geometries in the stability of rock slopes has been emphasized in recent research on high mountain slopes and large open pits. This paper documents the use of digital imaging techniques including laser scanning in the characterization of both step-paths and intact rock fracture in rock slopes. A combined finite element-discrete element code, ELFEN, is used to illustrate the factors influencing step-path failure in uniaxial laboratory specimens containing pre-existing weakness planes. Based on the results of the laboratory simulations step-path failure models of large open pit slopes are presented and the influence of intact rock bridge length, step-path overlap and fracture spacing discussed. The importance of considering step-path geometries for various translational failure mechanisms (planar, biplanar and toppling) are highlighted using the results of both numerical simulations and field observations.
Step-path failure mechanisms have become an increasingly important area of investigation at scales ranging from the micro- to macro-level. Figure 1 shows typical step-path geometries observed at the field (m) and laboratory (mm) scales. Numerous experimental fracture mechanics studies have attempted to describe the importance of en-echelon and step-path features in rock failure. The oil industry for example has long recognized the importance of such step-path or “zipper-like” fracturing in hydro- fracture. In rock slopes Jennings (1970) was the first to fully document their importance in open pit mining. Although this was followed by several probabilistic limit equilibrium developments to incorporate step-paths into rock slope design, comparatively little research has focused on the description of step-paths and intact fracture of rock bridges. The simulation of step-path failures has received new momentum with the development of deeper large open pits and their interaction with underground mines.