Post-Tensioned Anchor Stabilization at Cascade Lake Dam-PPT Presentation

PPT Presentation

Pdf Summary

Cascade Lake Dam, a family-owned, high-hazard arch dam built in 1920 near Asheville, North Carolina, did not meet modern dam-safety standards. With no original construction drawings, investigators surveyed the site and conducted subsurface work. Finite-element analysis showed potential sliding and overturning under extreme earthquake and probable maximum flood conditions, with a sliding factor of safety of 1.0. The dam’s shallow arch curvature, sloping foundation, and unkeyed contact with rock contributed to the concerns.<br /><br />The stabilization design used one sacrificial 30-strand anchor to verify assumed rock-grout bond strength and 14 production anchors, each with 20 strands, installed through the dam and into the foundation. The anchors were designed for 700-kip loads, with corrosion protection and bonded lengths tailored to the rock conditions.<br /><br />Construction required careful planning around restricted access, a narrow crest, lake-level control, and difficult anchor handling. The sacrificial anchor passed a 200% design-load test, confirming the bond-strength assumption. Grouting required measures to address seepage and voids, including low-pressure, staged placement. Excavation also revealed gravel fill beneath the left abutment, reducing arch action and making the structure behave more like a gravity dam. Analysis showed the proposed anchors were sufficient, so the final planned anchor was unnecessary. Production anchor testing met or exceeded specifications.<br /><br />Key lessons include involving the contractor early to address constructability, access, cost, and schedule; using geophysical surveys to identify concealed fill; and thoroughly investigating drilled holes—through water testing or downhole cameras—to anticipate voids and seams during grouting.

Keywords

Cascade Lake Dam

arch dam

dam safety

finite-element analysis

earthquake loading

probable maximum flood

stabilization anchors

rock-grout bond strength

construction grouting

foundation investigation