Dam safety modifications at Hoist and McClure Hydroelectric Dams

Abstract Only - Dam safety modifications to the Hoist and McClure hydroelectric dams, owned and operated by the Upper Peninsula Power Company, were completed during the summer of 2005. The dams are located on the Dead River in Marquette County in Michigan's Upper Peninsula. This rehabilitation project included raising a portion of the crest at the McClure Dam site, and some minor fascia rehabilitation. The primary purpose of the projects was the installation of rock anchors at both dams to resist possible sliding and overturning of the dams during extreme flood events. High capacity, multi-strand anchors were installed through the existing dams into bedrock. The rock anchors ranged in lengths from 70 to 100 feet with capacities ranging for 141 to 598 kips. Bedrock encountered at the McClure Dam site was generally massively bedded granodiorite, which proved favorable in both anchor installation and testing. Bedrock encountered at the Hoist Dam site was generally vertically foliated slate, which was a concern with the stresses to be incurred by the required high capacity anchors. Due to the age of the dams and other unanticipated conditions, the construction of some anchors proved challenging. Divers were needed to assist with anchor grouting. In addition, many of the anchor holes required pre-grouting to permeate and seal joints within the bedrock and concrete/bedrock interface. In the end, anchor proof and performance tests revealed ample capacity. While surficial work is addressed, the main focus of this presentation is design and installation of the rock anchors, jointly presented by STS Consultants and Hayward Baker.