Abstract The Dillon Dam, in Summit County, Colorado, is a large earth-fill dam constructed on a foundation of faulted and extensively jointed Mesozoic sedimentary rocks. Appurtenant features include a diversion tunnel and spillway shaft. Geologic features determined by preliminary exploratory drilling and by detailed studies during construction permitted close control of foundation excavation and grouting operations. Special problems were created by heavy water flows from pervious gravels up to 80 feet deep that covered bedrock in the valley floor of the Blue River, and by repeated movements of an ancient landslide reactivated during dam construction of loading by a temporary earth embankment and simultaneous excavation near the toe of the slide.

Abstract The Williams Fork Dam project consists of a thin arch dam constructed on top of an existing gravity-arch dam with appurtenant structures and power house. Foundation rocks consisted of granitic gneiss cut by lenses of mica schist and dikes. This case history reports on: (1) foundation excavation and characteristics of the granitic gneiss; (2) the consolidation grouting pattern and a detailed account of the record; (3) the cut-off, grout curtain; (4) dental-treatment formula used for detailed foundation treatment of the weathered zones; and (5) foundation geology of the West Dike consisting of young, poorly cemented clays and silts. The project demonstrates the interdependence of structural features in bedrock and the depth and degree of unsound weathered material, excavation and slope stability characteristics, and the grout consumption for consolidation.