Stability Analysis of Rock Slopes with Stochastic Fractures using Finite Element Limit Analysis

Rock slopes are commonly encountered in geotechnical engineering practice, and yet there is significant uncertainty when it comes to assessment of their stability, on account of the unknown extent of fracturing within the slope. Even where detailed mapping of fractures has been carried out on exposed rock faces, the unmapped extent of fracturing within the slope can still significantly affect its stability. This has previously motivated stochastic modelling of fractures, with Monte Carlo simulations carried out based on different, randomly generated discrete fracture networks (DFNs) to estimate a probability of failure for the slope. Until recently, displacement-based numerical methods such as the finite element method (FEM) have been used to perform such simulations under general loading conditions. However, convergence upon a strength reduction factor defining the onset of failure is not guaranteed when using FEM, and a much more efficient and reliable method of stability analysis under general loading conditions is finite element limit analysis (FELA). In this study, FELA is applied in probabilistic strength reduction analysis of two fractured rock slopes, with DFNs generated using a new algorithm that takes account of positions and orientations of fractures observed on exposed faces of the rock. Analysis of the second slope is also attempted using a commercial FEM package, and the advantages of adopting FELA over this approach are clearly demonstrated.

Keywords: Rock slopes, limit analysis, strength reduction analysis, discrete fracture networks, probabilistic slope stability analysis.