U.S. Fish & Wildlife Service Low Hazard Dams - Association of State ...

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U.S. Fish & Wildlife Service Low Hazard Dams - Association of State ...

STANDING OPERATING PROCEDURESarea around the boil to create an enclosure and backpressure over the boil, or constructinga filtered drainage berm over the boil.Figure 6-11: Filtered Drainage Berm at Toe of an Embankment DamIf a ring dike is constructed around the boil, it should not be built too high or it candevelop new boils outside of the affected area. The primary objective is to prevent theloss of embankment material with the seepage. The purpose of the ring is to raise a headof water over the boil to counterbalance the upward pressure of the seepage flow. Theheight of the water column is adjusted so that the water exiting the boil runs clear and nolonger removes soil from the dam foundation. It is important that the flow of water is notstopped completely, as this may cause additional boils to break out nearby. Treated areasshould be kept under constant surveillance until the water recedes. Sandbag rings are themost common method of constructing ring dikes, however concrete well rings, shortpieces of large diameter pipe, earth berms, sheet piling, etc., can also be used. A sandbagring levee around a boil is illustrated in Figures 6-12 and 6-13.6-13Revision No. 0October 2008

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