An Evaluation of Piping Through Embankment Dams

Many embankment dams on soil and fractured rock foundations have failed due to the formation of pipe-shaped discharge channels or conduits at or near the contact with the foundation material. Piping within a dam structure may be defined as soil or embankment particles eroding along unseen conduits or pipes through a dam or its foundation by seeping water. Teton Dam is a good example of an embankment failure caused by piping. Ochoco Dam represents a good example of a dam that had piping problems but those problems were identified and rectified before a disaster occurred. Agency Valley Dam has several characteristics that are favorable to piping. An evaluation of Agency Valley Dam is undertaken to determine the potential for piping. A field investigation using drill holes and test pits acquired samples that were analyzed based on filter criteria. Seepage analysis provided phreatic water surface data and gradients at contacts within the dam and its foundation. A review of construction documents led to information about the condition of the outlet works tunnel. Visual inspection of the dam and toe drains yielded an overall condition of the dam. Evaluation of Agency Valley Dam show that the dam is functioning properly and the potential for piping under current conditions is very low