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subdrain be constructed as a blanket drain to collect and <br />• conduct the subsurface water away from the embankment. The <br />drain should be located about thrity (30) feet uphill From <br />the toe of the fill to the downhill edge of the drain. The <br />blanket drain should be at least ten (10) feet wide with a <br />thickness of at least one and onE• half (1.5) feet. A <br />schematic of the drain blanket concept is shown on Figure 1. <br />The blanket drain should extenL3 ar_ross thc• entire aro~l of fill. <br />The drain blanket material :,hould be gradod aggLrgatu <br />which is suitable as a filter material as well as ITrovide <br />adeyuate permeability fur drainal~c of scehaye wtltur. tJ r. <br />suggest you consider grading for the blanket drain material <br />as tabulated below. <br />PERCENT <br />• SIEVE SIZE PASSING <br />3/8" 100 <br />No. 9 70-100 <br />No. 8 50-100 <br />No. 16 30-85 <br />No. 30 15-60 <br />No. 50 10-30 <br />No. 100 2-10 <br />No. 200 less than 5 <br />As an alternative to the sand blanket, the drain msy be <br />constructed with a clean concrr:te gravel t}~at is wrapped by <br />-2- <br />M85021GE <br /> <br />Lambert anD ~l,osoeiateo <br />CONSULTING GEOTECH NIUL ENGINEERS ANG <br />M ATEflIAL TESTING <br />