Abstract:
Earthen dams are constructed to store water for the purposes of human consumption, food production, electricity production, industrial use and flood protection. Failure of Earthen dams may be due to hydraulic failure, structural failure or seepage failure. Hydraulic failure may be due to overtopping, erosion of the upstream/downstream surface/toe and piping. Structural failures can occur in either the embankment or the appurtenances. Failure of a spillway, lake drain, or other appurtenance may lead to failure of the embankment. Cracking, settlement, and slides are the more common signs of structural failure of embankments.
Seepage Failure occurs due to the uncontrolled seepage in both velocity and quantity. Water permeating slowly through the dam and progressively erode the soil in the embankment or the foundation toward the reservoir. Eventually with increased seepage flow rate the direct connection is made to the reservoir causing the piping. Piping may occur through the dam or the foundation causing dam failure.
Seepage problems in large dams should be addressed in proper way on time to prevent before it becomes a massive disaster. Field investigation and data evaluation reveal the type of seepage and its extent. Then the most appropriate remedial measures can be adopted. Construction of toe filter, toe drain, downstream seepage berm, conducting cement/clay grouting and Cutoff walls construction are more frequently practiced to prevent seepage through and beneath the dam.
Cutoff walls make the seepage paths longer, decrease the exit gradient at the toe and reduce the seepage quantities. Compacted impervious trench cutoffs, concrete cutoff walls, sheet piles, slurry trenches/cutoff walls are some different types of cutoff walls currently being utilized.
