The Dillon Dam Spillway Repairs Denver Water's Stainless Steel Spillway

Dillon Dam is a zoned earth-fill dam with a structural height of 310-feet located in Summit County, Colorado. The dam is located in the heart of Colorado's Summit County ski areas and winter conditions can be severe. The spillway, located the left abutment of the dam, has a "morning glory" ogee type crest and a vertical shaft which connects to the outlet tunnel. The spillway shaft concrete has experienced significant freeze-thaw damage since its completion in 1962. The 12 inch unreinforced concrete lining had deterioration depths of 4 to 6 inches in numerous areas. This type of damage is common with older spillways and other concrete structures located in cold climates and exposed to repeated freeze thaw cycles. The spillway deterioration at Dillon was monitored carefully for the last two decades. Two years ago, core samples were taken and a detailed analysis of the concrete condition was completed. Recommendations were made to conduct repairs as soon as practical because of both maintenance and dam safety concern. Two repair methods were developed and evaluated for the shaft liner repairs a reinforced concrete and a steel liner. The reinforced concrete alternative would replace the deteriorated concrete with new reinforced concrete surface. There were several construction concerns with this alternative including: ability to bond new concrete to the existing concrete because of seepage into the shaft through the rock; ability to meet the construction schedule because of the extensive grouting required; and the time required to form, place and the cure the concrete lifts. The second alternative was a 1-inch thick stainless steel liner grouted in place. The stainless steel liner was selected because it could be shop fabricated while the deteriorated concrete was being removed and the shaft prepared to accept the liner. The overlapping of these activities helped to shorten the construction schedule. The stainless steel liner eliminated all future maintenance in this portion of the repaired shaft. The liner needed to fit together almost perfectly so that sections could mate properly in the shaft as they were installed. The liner was installed in five pieces ranging in length from 32 to 12 feet and up to 60,000 pounds in weight. The project was a unique solution to a difficult repair and extended the service life of the spillway and dam by many years in a cost effective manner. 10 pp.