Seepage Control by Grouting under an Existing Earthen Dike

The Merimere Reservoir is a surface water supply source located approximately 3 kilometers northwest of the city of Meriden, Connecticut. The reservoir, constructed circa 1870, is impounded by an earthen dam to the north and by an earthen dike to the south. The earthen dike, which is the subject of this paper, has a concrete core wall and consists of fill resting on a low saddle of natural ground. The dike is approximately 45 m (150 ft) long and 6.6 m (22 ft) high. Evaluations of the reservoir revealed that the earthen dike was leaking at a rate of 950,000 to 1,135,000 liters per day (250,000 to 300,000 gallons per day). Several investigations were performed to determine the cause of leakage and provide remedial measures to reduce the seepage. The field investigations consisted of geologic mapping for outcrop joint trends, acoustic-emission monitoring, a seismic refraction survey, subsurface investigation and an investigation to locate the concrete core wall at the center of the dike. Bedrock outcropping at the west side of the dike is sandstone and at the east side is basalt. Based on the field investigations and engineering studies, it was concluded that the most probable location of the seepage was the highly jointed and faulted basalt along the eastern side of the dike. In order to reduce seepage through the basalt fractures, a pressure-grouting program was implemented. Cement grout formed a cutoff wall below and around the interface of the core wall and basalt bedrock. Grouting was performed in a triangular pattern in three rows with a spacing of approximately 1.5 m (5-ft). In order lo evaluate the effectiveness of the grouting program, a "V-notch" weir was constructed immediately downstream of a seepage boil prior to grouting. This weir was used to measure the quantity of the seepage flow before and after grouting in order to evaluate the reduction in the seepage and the effectiveness of the grouting program. The grouting program completed at the Merimere Dike markedly reduced the seepage around the dike by over 85 percent to approximately 80,000 liters per day (21,000 gallons per day), a level to which the city of Meriden has deemed acceptable.