In this study, a loosely coupled liquid-gas-solid three-phase model, linking two numerical codes, TOUGH2/EOS3, which is used for water-air two-phase flow analysis, and FLAC3D, which is used for mechanical analysis, was established. The results highlight the difficulty of predicting whether the pore water pressure is overestimated or underestimated when using simplified approaches, and it is concluded that predicting the pore water pressure distribution in a slope after rapid drawdown requires a coupled flow-deformation analysis in saturated and unsaturated porous media.Ībstract: Generally, most soil slope failures are induced by rainfall infiltration, a process that involves interactions between the liquid phase, gas phase, and solid skeleton in an unsaturated soil slope. This is achieved by combining laboratory test results and a back analysis of pore water pressure time records during a period of reservoir water level fluctuations. A key aspect of the case is the correct characterization of permeability of a representative soil profile. Then, a recent case of a major landslide triggered by a rapid drawdown in a reservoir is interpreted. Field records indicate that classical undrained calculations are conservative but unrealistic. In the second case study, a similar analysis is performed for the upstream slope of the Glen Shira Dam, Scotland, and numerical results are compared with field measurements during a controlled drawdown.

Simple methods, such as the undrained analysis and pure flow analysis, implicitly assuming a rigid soil skeleton, lead to significant errors in pore water pressure distributions when compared with the coupled flow-deformation analysis. To do that, a single slope subjected to a drawdown is first analyzed under different calculation alternatives, and numerical results are discussed. The aim of the study is to evaluate different approaches available for calculating pore water pressure distributions during and after a drawdown.

Abstract: In this paper, the rapid drawdown scenario is analyzed by means of numerical examples as well as modeling of real cases with in situ measurements.

Dam first impounding flac3d examples