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-18- <br />• <br />be in-place for periods beyond the present design life, we believe <br />than an embankment drain is well justified. For this reason, we <br />recommend providing a drain of the dimensions shown on Fig. 9. <br />The drain should be constructed of free-draining sand and gravel. <br />The drain should not contain more than 3 percent material passing <br />the No. 200 sieve. In order to minimize the cost of the drainage <br />material, it is possible to construct the embankment drain of a <br />coarse, open-graded sand or a combination of sand and gravel, <br />wrapped in a drainage fabric. The purpose of the drainage fabric <br />is to prevent infilration of fines into the drain. In our opinion, <br />this procedure is desriable on a small dam because of the cost of <br />developing a select, graded material. We recommend the construction <br />• of the downstream embankment drain using MiraEi 140 on both sides <br />of the embankment drain. The drain itself can be constructed from <br />clean sands and gravels with a maximum of 3 percent passing the No. <br />200 sieve. The recommended gradation on Fig. 9 corresponds to <br />3/4-inch concrete aggregate specifications. Sandier materials will <br />also be accpetable. An alternate recommendation is also given on <br />Fig. 9 The embankment drain should have a minimum thickness of <br />17 inches. A toe drain should be constructed at the downstream edge <br />of the embankment drain. The toe drain should consist of an open- <br />joint or perforated file pipe, encased within the embankment drain. <br />The file toe drain should lead to a point of positive discharge of <br />the seepage. <br />• <br />