Bedrock Settlement beneath a Large Embankment Dam: Fid-Bau Portal

Bedrock Settlement beneath a Large Embankment Dam

Huzjak, Robert J. / Prochaska, Adam B.

Predicting deformation of embankment dams and ancillary facilities during and post-construction is a critical design consideration. Total and differential settlements of these structures are generally evaluated based on consideration for immediate settlement and consolidation of the embankment materials and the soil foundations, with minimal consideration of bedrock settlement. However, bedrock in many parts of Colorado consists of geologically young (less than about 100 million 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 field and laboratory data, analyses, and design features that were incorporated to accommodate bedrock settlement below Frank Jaeger Dam, a 61-meter-high (200-foot-high) embankment dam that was recently constructed in two phases on a claystone bedrock foundation near Parker, Colorado. Bedrock settlement was initially computed using one-dimensional manual calculations and two-dimensional finite-element methods. Data obtained from instrumentation and monitoring during and after the first phase of construction were used to calibrate laboratory-obtained settlement properties to observed behavior. These calibrated properties, and the time since completion of the first construction phase, were used to predict the ultimate settlement for the foundation of the completed embankment. Features incorporated into the embankment and the ancillary facilities to accommodate the predicted construction and post-construction bedrock settlement and the performance and reliability of settlement sensors will be described. Bedrock settlement measured during and after completion of the embankment is compared to the predicted settlement.