Journal of Earth Sciences and Geotechnical Engineering

Dam Safety Problems Related to Seepage

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• Abstract

   

  Dangerous occurrences affecting dams take multiple forms, but seepage caused cases are the most numerous. Some of the cases are related to the geology of the foundation and the magnitude and type of discontinuities in the rock mass of the dam. Other are mainly due to of construction material in earth fill dams. Seepage occurs in all earth fill dams regardless of its materials, and seepage water can daylight at the downstream face causing erosion, piping and sloughing and instability; unless certain measures are taken. Instability can be controlled mainly by adding, filter material zones at the contacts with the clay core, chimney filter drain at the downstream part of the dam, filter zone or bench at the toe together with the drainage blanket under the downstream part of the dam. Seepage within the dam is enhanced by cracks which may result from uneven settlement of the dam due to different elastic behavior of the foundation materials, hydraulic fracturing, and differential settlement of parts of the dam or due to ground shaking in earthquakes. Preferential seepage paths can develop in such cracks, especially if the fill material is dispersive or suffusive. Similarly, such paths may develop along the contact surfaces of conduits installed under dams as outlet structures due to the low degree of compaction as a result of narrow trench dimensions. Using properly designed filter and drainages can reduce seepage quantities and the erosive force which causes internal erosion. In dam’s foundation grout curtains or other type of cutoffs can reduce the hydraulic head and hence uplift under the dam and hinder seepage.  Drainage, however, remains as the most efficient method in controlling this uplift in artesian conditions under dams, especially under concrete gravity dams. Generally, such drainage may take the form of drainage blanket and use of filters material. 

  Keywords: Seepage, Internal Erosion, Piping, Sloughing, Hydraulic Fracturing, Filters, Chimney Drain, Drainage, Uplift.