Numerical Slope Stability Analysis of Deep Excavations Under Rainfall Infiltration

Rainfall leads to the deterioration of slope stability conditions, while intense rainfall has been commonly associated with landslides on natural or engineered slopes. Deep excavations, typically related to geo-resources exploitation, e.g., in the case of surface mining, are often affected by rainfall events that jeopardize their stability. In this work, rainfall infiltration is directly incorporated in the slope stability analysis; this investigation is currently missing from the literature as mainly empirical methods are used regarding deep excavations. The very deep slopes from lignite mines are employed as typical examples, often reaching 200 m and presenting smooth inclinations and fine-grained soils. A general numerical framework was used; the safety factor’s deterministic analysis was supplemented by a Monte Carlo investigation to determine the probability of failure. The importance of the involved parameters—slope geometry, rainfall intensity, and soil properties—was studied through a parametric analysis. Initially, a typical slip surface is presented, relatively deep and reaching from toe to crest. The critical mechanism was the development—after the rainfall—of a smaller and more local than the initial (before rainfall) slip surface. Although the final surface is smaller than the initial one, it can be more than 50 m high denoting a significant hazard. The most influential parameters are rainfall intensity, soil permeability, and slope height. This study can serve as a basis for similar preliminary analysis in practice. Stability and reliability analysis reveals the need to supplement conventional safety factors with the probability of failure for a broader and improved overview.