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I I I I I I I I I I I I I I I I I I I Geotechnical Engineering Investigation GEOTECHNICAL ENGINEERING INVESTIGATION FOR CONTINENTAL DAM ffiNSDALE COUNTY, COLORADO I. Introduction A. General This report presents the results of our geotechnical investigation for Continental Dam located in Hinsdale County, Colorado as shown on the Vicinity Map, Figure 1. The purpose of our investigation was to evaluate the subsurface soil and rock conditions, perfonn stability and seepage analyses and provide recommendations for remedial action to improve stability and to control water seepage. B. Project Description Continental Dam was built between 1925 and 1926 as a compacted, zoned earthfill structure with a crest length of 31 0 feet, height of 92 feet and a crest width of 18 feet. The crest is at elevation 10,290 feet. The core contains a socketed reinforced concrete cutoff wall, clay core and downstream filter section. The downstream shell is composed of compacted, gravelly sand fill and slopes at 2H: IV. A 70 foot long, 15 foot thick rock benn with a reinforced concrete headwall reinforces the toe of the downstream face. The upstream face slopes at 2.5H: I V between the crest of the embankment and elevation 10,270 feet and 3H: I V from elevation 10,270 feet to the base of the dam. An "As Built" profile and section are shown on Figure 2. In 1990 an impervious geotextile blanket was placed on about 1/3 of the upstream face and extended about 150 feet along the left abutment, between elevations 10,282 and 10,250 feet, refer to Figure 3, Plan View, Dam and Outlet Conduit. The spillway is a 495-foot long reinforced concrete structure with crest elevation at elevation 10,279 feet and is located along the right abutment. The spillway is trapezoidal in shape with 45 degree side slopes and bottom width between 10 and 20 feet along the upstream portion and transitions to a rectangular shape at the embankment crest. Continental Dam Page 1