Geotechnical Design And Construction Issues For Guanella Dam, Near Empire, Colorado

摘要

Guanella Dam is a new 34-foot (10-meter) high, zoned earthfill embankment dam completed in the fall of 2003 and put into service in 2004. The dam was designed and constructed using a fast-track approach to meet water needs of the City of Golden. The dam is located near Empire, CO at the site of a previous aggregate quarry operation. The off-channel reservoir created by the dam will impound a water supply of about 2,140 acre-feet (2.64 million cubic meters). Several unique site conditions presented interesting geotechnical challenges that had to be overcome to develop a successful project. The site stratigraphy varied significantly over short distances, and the dam alignment was carefully selected to take advantage of a high ridge in a low permeability silt layer. On-site soils had to be carefully evaluated to allow for economic development of embankment materials. Because ground water was very shallow, a soil-bentonite seepage barrier wall through a foundation sand and gravel layer was selected to connect the embankment Zone 1 core to the foundation silt layer. The barrier wall was constructed using slurry trench methods. Finally, the highly pervious sand and gravel deposits in the quarry area extended away from the reservoir, beneath the adjacent creek. The seepage barrier wall beneath the dam had to be extended across the adjacent creek valley through these deposits to limit reservoir leakage. However, to allow for expedited permits, the valley cutoff wall had to include two "windows" to avoid working in the creek or in the embankment of adjacent US Highway 40. Seepage analyses were completed to verify that the partial valley cutoff wall would produce acceptable leakage rates.