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MINIMUM ONE FOOT THICK LAYER OF <br />LOW PERMEABLILITY SOIL IF NOT <br />COVERED WITH AN IMPERMEABLE SURFACE <br />MINIMUM ONE FOOT WIDE LAYER OF <br />FREE DRAINING MATERIAL <br />' (LESS THAN 5% PASSING THE #200 SIEVE) <br />OR <br />PROPERLY INSTALLED PREFABRICATED DRAINAGE COMPOSITE <br />' (MiraDRAIN 6000 OR APPROVED EQUIVALENT). <br />a <br />-FILTER MATERIAL - MINIMUM OF TWO <br />CUBIC FEET PER FOOT OF PIPE. SEE <br />BELOW FOR FILTER MATERIAL SPECIFICATION. <br />ALTERNATIVE: IN LIEU OF FILTER MATERIAL <br />TWO CUBIC FEET OF GRAVEL <br />PER FOOT OF PIPE MAY BE ENCASED <br />IN FILTER FABRIC. SEE BELOW FOR <br />GRAVEL SPECIFICATION. <br />FILTER FABRIC SHALL BE MIRAFI 140 <br />OR EQUIVALENT. FILTER FABRIC SHALL <br />BE LAPPED A MINIMUM OF 6 INCHES <br />-ON ALL JOINTS. <br />- MINIMUM 4-INCH DIAMETER PVC SCH 40 OR ABS CLASS SDR 35 WITH <br />A CRUSHING STRENGTH OF AT LEAST 1,000 POUNDS, WITH A MINIMUM <br />OF 8 UNIFORMLY SPACED PERFORATIONS PER FOOT OF PIPE INSTALLED <br />WITH PERFORATIONS ON 8O1TOM OF PIPE. PROVIDE CAP AT UPSTREAM <br />END OF PIPE. SLOPE AT 2 PERCENT TO OUTLET PIPE. <br />4 <br />4 <br />"FILTER MATERIAL" TO MEET FOLLOWING SPECIFICATION <br />OR APPROVED EQUIVALENT: (CONFORMS TO EMA STD. PLAN 323) <br />"GRAVEL" TO MEET FOLLOWING SPECIFICATION OR <br />APPROVED EQUIVALENT: <br />MAXIMUM <br />SIEVE SIZE PERCENTAGE PASSING SIEVE SIZE PERCENTAGE PASSING <br />1" 100 11/2"100 <br />314"90-100 NO. 4 50 <br />NO. 200 8 <br />SAND EQUIVALENT = MINIMUM OF 50 <br />3/8"40-101 <br />NO. 4 25-40 <br />NO. 8 18-33 <br />NO. 30 5-15 <br />NO. 50 0-7 <br />NO. 200 0-3 <br />RETAINING WALL BACKDRAINS <br />GRADING GUIDE SPECIFICATIONS <br />NOT TO SCALE ..- SOUTHERNDRAWN. JAS <br />CHKD: GKM dilm| _ _ CALIFORNI.81* GEOTECHNICAL <br />PLATE D-7