INVESTIGATING THE SUBSURFACE STRUCTURE OF THE CHESTNUT HILL EMBANKMENT DAM USING THE GROUND PENETRATING RADAR (GPR) METHOD

Information of the subsurface structure of the Chestnut Hill Reservoir earth embankment dam is needed to evaluate the long term integrity of the dam for water storage and flood prevention. Geophysical tools provide a non-invasive method of investigating subsurface structures of the earth. The GPR geophysical method was conducted to image the subsurface structures of the dam. The GPR method uses high frequency, pulsed electromagnetic waves to image the subsurface with high-resolution. In this study, the GPR survey lines were taken along the dam embankment at the two ends of the dam. Profiles of the dam were also taken across the dam embankment at intervals of about 35m to form a three-dimensional subsurface image of the dam. The profiles along the dam show the locations of buried pipes close to the two block houses on the dam. At about 385m into the profile, which is at the midpoint of the two block houses, there were some prominent diffractions at a depth of about 2-2.5m. Also some diffractions were seen at a distance 625-680m, which is the region of the second block house. These diffractions are close to the surface at about 0.5m depth and extend to a depth of 1.5m. These diffractions are probably due to the presence of pipes within the dam.