SEEPAGE CONTROL IN EARTH DAMS

The basic methods for controlling seepage are listed, and the need for a conservative approach in designing dams to resist seepage is emphasized. Zoning alone may not ensure control over seepage if the permeability of the downstream zone is less than 100 to 500 times that of the upstream impervious core, foundation and abutments (depending on the width of the core), or if there is a high degree of stratification in the dam. Internal drain systems offer more positive control over seepage than does zoning, but they must be correctly designed and carefully constructed. Graded filter dams can ensure adequate discharge capacities as well as filter protection, usually at less cost than single layer drains. Important earth dams should be instrumented with piezometers, observation wells, and seepage measuring devices. If it is found necessary, corrective measures should be taken after the dam has been tested in service. In a discussion of the prevention of piping failures, consideration is given to filter criteria, the prevention of blowup or heave, and problems associated with natural heave. Recommendations are made for preventing piping natural formations in embankments, and around drains. Problems associated with the construction of embankments and drains are discussed. Seepage reducing methods are detailed. Such methods are, however, not sufficient alone, and should be combined with some form of drainage.