Construction of Brush Hollow Dam Rehabilitation and Repair of Crushed Outlet Pipe

Brush Hollow Dam was constructed as an off-stream irrigation reservoir in Penrose, 1922-23. The dam was constructed as a homogeneous clay embankment with a high-plasticity “puddle clay core” cutoff to the bedrock foundation. The outlet was a single 36-inch diameter concrete-encased steel pipe with a hydraulically controlled slide gate at the upstream end. The outlet pipe was supported on a concrete pier founded on bedrock where the pipe crossed the core trench. The dam experienced repeated problems in the first several years following completion, including a sinkhole on the downstream slope, partial crushing of the outlet conduit, several slides on the upstream slope, significant foundation settlement, upstream movement of the crest, and longitudinal cracking along the crest. Following repairs to the early problems, the dam performed adequately for about 65 years. In August 1993, a 600-foot long crack was discovered downstream of the crest, and the dam was judged to be in a condition of incipient failure. The reservoir was drained, and rehabilitation of the dam was undertaken. A dam rehabilitation design was developed which included an upstream slope buttress, a rock-filled foundation trench keyed into natural soils to support the buttress, extension of the outlet pipe to a new intake structure, and a grouted pipe liner in the crushed outlet pipe. The spillway was enlarged to provide increased flood capacity, as required by state dam safety regulations. Several problems were encountered during design and construction of the repairs for this “old” dam. This paper presents the elements of the dam rehabilitation design, the outlet pipe repair design, and a discussion of conditions encountered during construction. 10 pp.