Abstract
ABSTRACT Presence of pervious strata in the foundation of an earthen dam would pose a serious problem of seepage. Maskinala earthen dam in Raichur District of Karnataka was constructed on pervious foundation by providing partial cut-off and upstream blanket. Post construction detailed foundation investigation indicated presence of 2.0 to 8.0 m sand stratum underlain by 2.0 m thick highly pervious sand-gravel followed by impervious rock. Finite element steady seepage analysis for the dam and foundation indicated that the value of the exit gradient would be within the permissible limits. However, the quantity of seepage would be excessive after impoundment. This warranted additional defensive measures against seepage in the form of cut-off wall/diaphragm wall/slurry trench/geomembrane at the upstream toe and it should be embedded at least 1.0 m in impermeable bedrock. This would act as a positive cutoff. Since seepage quantity with this provision was found to be acceptable, suggestion for construction of a positive cut-off at upstream toe was recommended. Installation of piezometers in foundation and in the body of the dam was suggested to monitor performance of the earth dam after impoundment.
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