6.3 Hybrid approach
Hybrid approaches are increasingly being adopted in rock slope analysis. This may include combined analyses using limit equilibrium stability analysis and finite-element groundwater flow and stress analysis as adopted in GEO-SLOPE (Geo-Slope 2000). These models have been used for a considerable time in underground rock engineering including coupled boundary finite element and coupled boundary-distinct element solutions. Recent advances include coupled particle flow and finite-difference analyses using PFC3D and FLAC3D (Itasca 1999).
The coupling of finite-distinct element codes, for example in ELFEN (Rockfield 2001), allows modeling of both the intact rock behaviour and the development and behaviour of fractures (figure 8). These methods use a finite element mesh to represent either the rock slope or joint bounded blocks coupled together with discrete elements to model deformation involving joints. If the stresses within the rock slope exceed the failure strength within the finite-element continuum, a discrete fracture is initiated. Adaptive remeshing allows the propagation of the cracks through the finite-element mesh to be simulated. Coupled finite-/distinct element models are able to simulate intact fracture propagation and fragmentation of jointed and bedded rock (figure 9). However, complex problems require high memory capacity, comparatively little practical experience in use and requirement of ongoing calibration are major constraints.
Figure 8: Hybrid finite-/discrete-element rockslide analysis showing several progressive stages of brittle failure (from Eberhardt et al. 2002).
Figure 9: 3D Simulation of Rock fall using hybrid approach