Postconstruction Deformations of Rockfill Dams

Abstract

Postconstruction deformations of some rockfill dams with a slightly inclined or central till (moraine) core are presented. Although deformation still continues, even 30 years after dam construction, for all practical purposes the settlement could be nevertheless considered to cease 36 months following the end of construction. The crest settlement reflects the core compression, which is relatively low, while the downstream rockfill shoulders exhibit much higher settlements. The maximum settlement expressed as a percentage of height (%H) does not always concur with the maximum measured settlement value or with the maximum fill height. Depending on the valley cross section (width), an arching phenomenon can develop and push the maximum %H towards the abutments. Horizontal deflection downstream also expressed as a percentage of the height of the dam crest could reach 1.5–5.0 times the settlement value. The effect of impounding is illustrated by a differential deformation (settlement and deflection) of the upstream and downstream edge of the crest, inducing a progressive spreading (widening) of the crest (danger of longitudinal fissuration). Settlement and deflection envelope curves based on the values recorded by the analyzed structures could be used as a quick tool for monitoring the future behavior of dams and dikes.