Assessment of remedial measures to reduce exceedance probability of performance limit states in embankment dams

Results of a series of numerical analyses, simulating three remedial measures applied to an embankment dam, are used to investigate the extent of lessening the severity of the distress level under flood loading. Conceptually, the three remedial measures are increasing the mean effective stress, adding a low permeability curtain to limit seepage, and improving drainage to lower pore water pressure magnitudes at key locations. The results are presented in the context of exceeding predefined limit states in terms of toe deformation and hydraulic gradient. Constructing a downstream berm has a significant impact on the exceedance probabilities of the deformation limit states at the toe, but a small impact on the toe gradient values. Adding a low permeability curtain below the dam crest considerably reduces both deformation and gradient magnitudes in relation to the predefined limit states. This occurs due to an increased seepage path leading to a higher drop of pressure head and lower phreatic surface level; these two effects result in lower shear strains and less deformations at the toe. Improvement was observed by adding the toe drainage system with a hydraulic conductivity that is 4–20 times higher than the hydraulic conductivity of the embankment material. In this case, the exceedance probabilities of deformation limit states decrease and the impact is higher for a higher hydraulic conductivity of the drainage system compared to the embankment soil. Given the analyses configurations and parameters, constructing a berm at the toe leads to the lowest exceedance probabilities, in terms of deformation limit state, and thus seems to be the most effective approach among the three analyzed remedial measures.