Modelling and analyses of rock bridge fracture and step-path failure in open-pit mine rock slope

Rock Bridge fracturing and coalescence with pre-existing discontinuities in rock mass due to the initiation, propagation and interaction of these fractures refers to instability mode of step-path failure. Step-path failure is a typical type of instable mode of man-made and natural rock slopes. The continuum finite element method was applied to work on deeper insight into the propagation of tensile cracks which developing in the intact rock bridges that can finally coalesce to form step-path failure. In this paper, based on the intact rock fracturing hypothesis, two selected slope simulations from the Handlebar Hill open - pit mine near Mt. Isa in Queensland, Australia, modeled the process of fracturing and step-path failure through different pre-existing discontinuities. The empirical models of Bobet and Einstein (1998) and the progressively cracks development are observed within crack initiation, propagation and coalescence in the intact rock bridges. Proposed slope models of the mine included four joint-net distributions through the rock masses considering the geometry of structures (dip angles, spacing, lengths and orientation) illustrated the extension cracks from the flaw tips and propagated to the slope surface. Modes of intact rock bridges fracturing (shear, tensile and a combination of shear and tensile) have been observed. Tensile fracture is usually generated when the rock bridge angle is sub-vertical. Shear fracture can be initiated in less steep rock bridge angles. A combination of shear and tensile failure is normally generated in slopes with. Slope with explicit large-scale structures of steeper dip angles increased the yielding. Larger structures show much higher potential for yielding as the tensile stresses increasing. Major joint plane spacing resulted in less potential for relative deformations between neighboring structures and consequently reduced slope instability. The changes of length and spacing have more influence on slope stability than a change in the dip angle of the structures. © 2019, Springer Nature Switzerland AG