Influence of Anisotropic Permeability on Slope Stability Analysis of an Earthen Dam during Rapid Drawdown

The operation of dams at times requires a sudden decrease in the existing reservoir level. This abrupt change in the upstream water level, known as rapid drawdown, results in the development of unbalanced forces and occasionally causes catastrophic failure of the upstream shell. The drawdown-induced slope stability analyses are typically performed assuming that geomaterials used to build the dam exhibit isotropic permeability; even though, in reality, the geomaterials mostly exhibit anisotropic properties. The principal objective of this study is to comprehend the impact of anisotropic permeability on the drawdown-induced stability analysis of earthen dams and assess the impact of erroneously assuming isotropic permeability properties for numerical analyses. The influence of dam geometry, rate of drawdown, and depth of reservoir water before drawdown were also studied. The results of this research study highlight that the assumption of isotropic permeability inevitably leads to erroneous estimation of deformations incurred during drawdown. The extent of error was observed to increase with an increase in the dam slope and drawdown velocity.