ASDSO 2015 A Race Against Mother Nature, Emergency Dam Safety Repairs at 11,000 feet

摘要

Ivanhoe Dam is located about 12 miles west of Leadville, Colorado in Pitkin County, just west of the Continental Divide at an elevation of about 11,000 feet. Emergency dam safety repairs were required at the dam due to significant deterioration of the outlet works structure resulting in noticeable piping of embankment material through the release pipe. The dam safety problem was first notice during a State inspection in July of 2014, and given the notably high elevation of the dam, the race against Mother Nature had started. The Owner, Busk-Ivanhoe Water System Authority (Authority), was forced to bid the job, select a contractor, mobilize to the remote site location and complete substantial construction of the project in a few months, before significant snow accumulation shuts down construction, which is typically the end of October. The dam was a homogenous embankment dam before construction, about 16 feet high, approximately 270 feet long, and impounds approximately 750 acre-feet. The dam also has an upstream seepage barrier system that consists of a layered system of geotextiles, geo-membrane, and geo-web. The dam is classified as a significant hazard structure by the State of Colorado, Office of the State Engineer, Dam Safety Branch (SEO). The reservoir is generally filled with uncontrolled spring runoff from the basin above the dam and from the three collection canals. As such, repairs of the dam needed to be complete prior to the winter shut down and the ensuing uncontrolled spring runoff. The major modifications to the dam included replacing the existing damaged outlet works 48-inch-diameter corrugated metal pipe (CMP) with a new 36-inch-diameter steel pipe; replacing the existing intake structure with a new concrete intake structure that includes a service spillway; constructing a downstream stability berm; adding a chimney filter, drain blanket and toe drain for seepage control; repairing the seepage barrier system, and replacing the emergency spillway control weir. This paper documents all of the designed features for the Ivanhoe Dam Rehabilitation Project, the challenges experienced during construction, the existing construction progress, and lessons learned during the project.