Slope stability under rapid drawdown conditions
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The rapid drawdown condition arises when submerged slopes experience rapid reduction of the external water level. Classical analysis procedures are grouped in two classes: the “stress-based” undrained approach, recommended for impervious materials and the flow approach, which is specified for rigid pervious materials (typically a granular soil). Field conditions often depart significantly from these simplified cases and involve materials of different permeability and compressibility arranged in a complex geometry. The drawdown problem is presented in the paper as a fully coupled flow-deformation problem for saturated/unsaturated conditions. Some fundamental concepts are first discussed in a qualitative manner and, later, explored in more detail through the analysis of two embankment dams. In Shira earthdam pore pressures were recorded at different points inside the embankment as a consequence of a controlled drawdown. Predictions of four calculation procedures (instantaneous drawdown, pure flow, coupled flow-elastic and coupled flow-elastoplastic, all of them for saturated/unsaturated conditions) are compared with measured pressure records. Only the coupled analysis provides a consistent and reasonable solution. The case of a large landslide, immediate to a reservoir, reactivated by a condition of rapid drawdown is also described in the paper.
CitacióAlonso, E.; Pinyol, N.M. Slope stability under rapid drawdown conditions. A: Italian Workshop on Landslides. "First Italian Workshop on Landslides". Napols: 2009, p. 11-27.