Investigations and Remediation of the Reservoir Foundation at the Ludington Pumped Storage Plant

The Ludington Pumped Storage Plant is a 1872 MW hydroelectric facility located along the eastcentral shore of Lake Michigan near the town of Ludington, Michigan. The plant structures include a 842 acre (341 hectare) upper reservoir lined with a clay blanket that is 3 to 10 ft (0.9 to 3 m) thick. Beginning in 1973, visual and diver inspections revealed linear trench-like features in the clay liner that were found to penetrate into the underlying foundation. Concerns for dam safety led to extensive geotechnical investigations to determine the cause of the trench features and to develop an appropriate remedial design. Data from field and laboratory investigations and reviews of historical data showed that the trench features were likely caused by a combination of differential settlement, hydraulic fracturing, and migration of fines. A multi-year remedial program was initiated in May 1992 to fill the trench features with a non-plastic, fine-grained silica of a specified gradation that would stabilize the trenches and adjust with time to fill deeper voids and cracks, thereby minimizing conditions that could lead to further deterioration of the reservoir foundation. Side-scan surveys, diver inspections, groundwater monitoring, and reservoir seepage tests indicate that many of the trench features have been stabilized and seepage through the reservoir bottom has been greatly reduced.