Earth dams and embankments are used around the world to protect structures and facilities in low-elevation areas. If the phreatic surface intersects the downstream slope, the embankment is likely to fail, potentially resulting in enormous losses to life, infrastructure, and the environment. Drainage blankets are typically placed downstream to prevent the phreatic surface from intercepting the downstream slope. In the United States, the US Department of Interior requires a minimum of 10 feet clearance between the phreatic surface and embankment’s downstream slope. The length of the drainage blanket to ensure this condition is typically estimated using a cumbersome and inefficient trial-and-error approach, assuming various blanket lengths until a satisfactory clearance is achieved. This paper presents a closed-form solution to the problem using a newly-developed formula to determine the blanket length for any specified clearance, which represents a significant advancement over the conventional trial-and-error graphical approach. Using the model presented in this paper, the quantity of seepage can also be estimated without the need to develop a flow net.
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