Stability Analyses for a 200-foot-high Dam Requiring Staged Construction: Fid-Bau Portal

Stability Analyses for a 200-foot-high Dam Requiring Staged Construction

Huzjak, Robert J. / Friend, Edwin R. / Prochaska, Adam B.

Frank Jaeger Dam, located in Parker, Colorado, was originally designed to be constructed in two phases with up to 20 years between each phase. The original zoned earthen embankment dam was to be 41 m (135 feet) tall with an ultimate height of 61 m (200 feet). The dam included upstream and downstream stability berms and would be enlarged with a downstream raise. For technical and economical reasons, the 15-meter (50-foot) thick downstream stability berm was random fill, which included a broad range of clayey and sandy soils. During construction of the initial phase, the owner elected to move directly into design and construction of the second phase. The second phase of the embankment would require up to 43 meters (140 feet) of fill over the stability berm. The design of the enlarged embankment needed to consider the strength of clayey materials in the berm to ensure construction slope stability and to accommodate impacts from berm settlement on the embankment. Field investigations and laboratory testing were preformed to characterize the clayey materials in the berm. Stability and settlement analyses were completed during design to identify the required berm strength to provide acceptable construction stability and to predict the time necessary to achieve the required strength. The resulting design included multi-staged embankment construction requirements and various types of instruments to monitor settlement. The predicted rate of consolidation and associated strength gains closely matched field measurements and no claims or loss of time was experienced during construction. This paper will present the field and laboratory data, design and construction phase analyses, construction monitoring data, reliability of various settlement monitoring methods, and conclusions about the design predictions and embankment performance during construction.