The Effect of Core Permeability on Rapid Drawdown in Embankment Dams

In this paper, the effects of rate of lowering of reservoir water level, embankment geometry and constituent material engineering properties on the pore water pressure pattern in embankment areexamined with and without considering stress dependency of soil permeability. For this purpose, coupled transient seepage and deformation analyses were carried out. It was disclosed that, considering consolidation effects, the phreatic surface in clay core would change slower than if it was not taken intoaccount. For a 34 m wide and 59 m high clay core with very low permeability, say K = 10 -8cm/s, even a draw down rate as low as 1 cm/day, leads to occurring rapid drawdown. In the other hand if the core permeability is 10-5 cm/s rapid draw down will not occur provided that the rate of draw down is not greater than 5 cm/day. Consequently, from the view point of earth dam engineering, highly impermeable materials, such as high plasticity clayey soils, are not reasonable for using in core zone. Using achievements of this piece of work suitable drawdown programs may be set up for earth dams

Keywords:

Embankment dam , Rapid drawdown , upstream slope , permeability , consolidation