Abstract:
Cascade Lake Dam is a single curvature, concrete arch dam, located on the Little River near Brevard, North Carolina. The dam was constructed circa 1920 and is classified as a high-hazard structure by NC DEQ. The dam has a structural height of 58 feet and a length of 240 feet. The dam thickness is about 7 feet at the crest and 19.5 feet at the base.The dam has a vertical upstream face and a steeply sloped downstream face. The base of the arch appears to have been constructed directly on top of the riverbed, which slopes slightly downstream, and is not keyed into the foundation. This construction technique leaves the base of the arch susceptible to sliding at the base.
Assessments performed in 2015 revealed the structure does not satisfy current dam safety stability requirements. A finite element model stability analysis indicated that a pure overturning failure was not a probable failure mode. Rather, the analysis indicated, largely due to the geometry of the canyon, the dam was susceptible to “underturningâ€, where the downstream toe kicks out at the center of the dam and the upper portions remain restrained by bearing at the abutments.Â
To address this stability issue, 14 anchors were installed vertically through the dam’s crest anchoring it into the foundation rock. The anchors consisted of 20 post-tensioned strand anchors. Tight hole verticality requirements were required due to the dam’s relatively thin section. The narrow dam crest necessitated the construction of a temporary working platform cantilevered over the downstream edge of the dam crest.
Anchor installation, ongoing as of this writing, is anticipated to be completed in early 2025. These modifications are designed to meet regulatory guidelines and improve safety and stability at Cascade Lake Dam.