The use of Electrical Resistivity Tomography and Induced Polarization to investigate seepage conditions in a Hydroelectric Dam (A case study of the East Dike of the Kpong Hydro Dam)

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Earth dams are designed to permit the flow of seepage water from their reservoir through designed filter zones and relief wells. However, the flow of seepage water through other preferential flow paths either than the designed filter zones and relief wells can be detrimental to the overall stability of the dam. Conventional inspection methods such as surveillance and installation of instruments including inclinometers and settlement monuments are commonly used to detect anomalous conditions which can lead to failure on earth dams. These methods however usually detect these causes of failure after it has worsened. Geophysical techniques are non-invasive, cover a large area of the survey and are able to detect relatively small changes in physical contrast within an earth dam when used repeatedly. The ERT and IP methods were used to delineate possible seepage zones and pathways of unplanned seepage conditions that have occurred on the downstream side of the east dike of the Kpong Hydroelectric dam in Akuse, Ghana. Analysis of ERT results from the four traverse lines established along the east dike show significant anomalous conditions suggesting the existence of an unplanned seepage pathway within the lower sand and gravel overburden foundation of the dike. Very low resistivity zones (<25 Ωm) at different distances along the embankment was detected to be potential seepage zones. Also, the potential unplanned seepage pathway was delineated at an average elevation of 7m NDL and from 42m distance from the start of the traverse lines to 112m towards the end of the traverse lines. The IP results could not effectively detect and delineate the potential unplanned seepage zones and pathways.
A thesis submitted to the Department of Geological Engineering (Faculty of Civil and Geo-Engineering) College of Engineering in partial fulfilment of the requirements for the degree of Master of Science (Geophysical Engineering)
Electrical Resistivity Tomography, Induced Polarization, Investigatiom, Seepage conditions, Hydroelectric Dam, East Dike, Kpong Hydro Dam