Monitoring Seepage and Piping Occurrences in Earthen Embankment Dams Connected to Structural Deficiencies, Applying Near Surface Geophysical Methods.

In recent decades, as a response to numerous dam failures across the nation resulting in extensive property damage, the Department of Environmental Protection for New Jersey (NJDEP) bolstered its Division of Dam Safety and Flood Control. Adherence to guidelines and standards along with regular inspection from contracted engineering firms has proven successful in preventing catastrophic dam failures tied to large reservoirs. However, there has been a noted increase in small dam failures, particularly earthen structures that are unable to be routinely inspected. This research project relies on ground penetrating radar (GPR) profiles collected with a 270 MHz, shielded, monostatic GSSI system, and electrical resistivity surveys collected with a Geometrics OhmMapper capacitively coupled dipole (CCD) system with two receivers, to image the internal structure of potential at-risk earth dams in the Northern New Jersey area. Abnormal reflection returns in GPR profiles can identify points or zones of internal weakness where further material shifting or seepage may occur. Additionally, it is possible to identify whether present void spaces contain air or have already been inundated. Electrical resistivity profiles serve as an ideal complimentary technique. The expected uniform distribution of high resistivity dry to damp earthen material is starkly contrasted by low resistivity zones where preferential fluid flow, infiltration, or piping is actively occurring. Over-saturation resulting from these processes can reduce structural integrity and promote failure. Near surface geophysical techniques are validated with field site visual assessments of dam faces.