Anchoring of Little Quinnesec Falls Hydroelectric Dam

The Little Quinnesec Falls Hydroelectric Dam is located on Menominee River in Niagara, Wisconsin. It is owned and operated by Consolidated Papers, Inc. (Niagara Division). The dam generates about 10,200 kW of hydroelectric power. Under FERC re-licensing program extensive field investigations were performed. The field investigations involved coring through the gravity section of the dam and foundation rock, taking video of the boreholes using borehole camera and installing piezometers to monitor uplift pressure under the dam. The boreholes were between 8-m and 16-m in length. The interface between concrete dam and bedrock was found to be at a depth of 5-m to 8-m. The coring was performed up to 1.5 m into the bedrock. The bedrock was found to be Gneiss, light gray, coarse grained and massive. Complete water loss was noted in most of the boreholes through the dam. Dye tests indicated possible link between the boreholes and the upstream pool. The borehole camera also detected fine cracks and presence of timber at the interface between the concrete dam and the rock foundation. Based on these field investigations and subsequent analyses, stabilization measures were recommended. It included installation of vertical post-tensioned anchor system through the dam and the power plant. The work consisted of anchor installation, testing and stressing following successful performance testing of the anchors. Following stressing, secondary and final stage grouting was performed and the block-outs restored. This paper presents step-by-step procedure followed from field investigation to the installation of the anchors to fix the dam.