Abstract
The interaction among seepage, stress and stability of earth dams during impounding and drawdown of reservoir is investigated by a finite element procedure. The procedure is based on superposing between saturated-unsaturated seepage analysis and stress analysis. The finite element mesh employed in saturated-unsaturated seepage analysis remains invariant during iterative calculations. By using the same mesh in the stress analysis it is possible to evaluate directly the effect of body forces such as seepage force, buoyancy and surcharge due to saturation on the behavior of effective stresses within the dam. The dam is assumed to behave elastically after completion of construction. Using stress levels mobilized in the finite elements, values of safety factor along the circular slip surface are calculated to assess the stability of the dam. The strength of soil is described by Mohr-Coulomb's failure criterion.
Numerical results show that the stability of earth dams during impounding and drawdown of reservoir is strongly influenced by the change of principal stresses within the dam, and that the manner of this change is governed by the distribution of body force which occurs during seepage. The safety factors of the dam are given as a function of step during impounding of reservoir and time after drawdown. The stability of the dam with a horizontal drain is also examined.
