SETTLEMENT OF EMBANKMENT DAMS — DON'T FORGET ABOUT THEBEDROCK

摘要

Predicting deformation of embankment dams and ancillary facilities during and postconstruction is a critical design consideration. Total and differential settlements of thesestructures are generally evaluated based on consideration for immediate settlement andconsolidation of the embankment materials and the soil foundations, with minimalconsideration of bedrock settlement. However, bedrock in many parts of the world, andparticularly in the western United States, consists of geologically young (less than about 100million years old) fine grained sedimentary units. Under loads from moderate to large dams,settlement of this type of bedrock can become a critical design condition. This paper presents the analyses, field and laboratory data, and design features thatwere incorporated to accommodate bedrock settlement below a 200-foot-high embankmentdam that is being constructed in two phases on a claystone bedrock foundation. Construction and post construction settlement were computed using one-dimensionalhand and two-dimensional finite-element methods. Data obtained from settlement sensors,piezometers, and outlet conduit surveys during and after the first phase of construction wereused to calibrate laboratory-obtained settlement properties to observed behavior. Thesecalibrated properties, and the time since completion of the first construction phase, were usedto predict the ultimate settlement for the foundation of the completed embankment. Featuresincorporated into the embankment and the ancillary facilities to accommodate the predictedconstruction and post construction bedrock settlement will be described. Finally,recommendations for predicting construction and post construction bedrock settlement will bepresented.