Fig. 15.25 Downstream pore pressure in clay core
(iv) Steady Seepage at Full Reservoir Condition This condition develops when the reservoir is full and as such any shear slide would lead to a disastrous failure. Therefore, the stability analysis for this condition must be carried out more conservatively. The stability of the downstream slope should be analysed for this condition using the effective stress method and taking into account pore pressures owing to gravity flow. Pore pressures on account of changes in the embankment volume are not considered in the analysis, because the shear strains imposed on a well-constructed embankment are likely to dilate (i.e., expand the volume) the soil and reduce the pore pressures temporarily (13).
The following unit weights may be used for the calculation of driving and resisting forces when pore pressures are otherwise not included in the stability analysis (13).
