Rock moisture dynamics, preferential flow, and the stability of hillside slopes

Abstract

© Springer International Publishing Switzerland 2016. This chapter investigates the relevant hydrologic and geotechnical processes triggering failure of steep hillside slopes under rainfall infiltration. Despite decades of extensive study, the fundamental controls responsible for this commonly observed slope failure mechanism are yet to be quantified. The work focuses on the triggering mechanisms of slope failure induced by rainfall events and highlights the multiphysical nature of the problem. In hillside slopes, fluid supply from the rain and fluid input from the fractures of an underlying bedrock create moisture dynamics that could undermine the stability of slopes. The impact of such dynamics is difficult to predict, let alone quantify. In this chapter, the influence of rainfall input into the slope surface and the accompanying rock moisture dynamics are investigated using a hydromechanical model that couples the interaction between fluid flow and solid deformation. Both single-porosity and double-porosity formulations are employed, the latter formulation pertaining to the case where the solid matrix exhibits two dominant porosity scales. Nonlinear finite element simulations of the failure of hypothetical hillside slopes similar in configuration to the two well-documented test slopes, the CB1 and Ruedlingen test slopes, reveal the impacts of slope/bedrock topography, rainfall history, rock moisture dynamics, and preferential flow pattern on the failure of hillside slopes.