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JD-8 Mine-Drainage Design Plan 21 <br /> Attachment 2 <br /> Rip Rap Granular Bedding Specifications (from UDFCD 2011) <br /> DRAINAGE CRITERIA MANUAL(V 1) MAJOR DRAINAGE <br /> Table MD-11—Gradation for Granular Bedding <br /> Percent Weight by Passing Square-Mesh Sieves <br /> Type II COOT Sect. <br /> U.S.Standard Sieve Size Type I COOT Sect.703.01 703.09 Class A <br /> 3 inches -- 90-100 <br /> 11.inches ----- <br /> 'A inches --- 20-90 <br /> 36 inches 100 -- <br /> #4 95-100 0-20 <br /> #16 45-80 <br /> #50 10-30#100 2-10 <br /> #200 0-2 0-3 <br /> The Type I and Type II bedding specifications shown in Table MD-11 were developed using the T-V filter <br /> criteria and the fact that bedding which will protect an underlying non-cohesive soil with a mean grain size <br /> of 0.045 mm will protect anything finer. Since the T-V filter criterion provides some latitude in establishing <br /> bedding gradations,it is possible to make the Type t and Type II bedding specifications conform with <br /> Colorado Division of Highways'aggregate specifications. The Type I bedding in Table MD-11 is designed <br /> to be the lower layer in a two-layer filter for protecting fine-grained soils and has a gradation identical to <br /> Colorado Department of Transportation's(CDOT's)concrete sand specification AASHTO M-6(CDOT <br /> Section 703.01) Type II bedding,the upper layer in a two-layer filter, is equivalent to Colorado Division <br /> of Highways'Class A filter material(Section 703.09 Class A)except that it permits a slightly larger <br /> maximum rock fraction When the channel is excavated in coarse sand and gravel(50%or more of <br /> coarse sand and gravel retained on the#40 sieve by weight),only the Type II filter is required. <br /> Otherwise,a two-layer bedding(Type I topped by Type II)is required. Alternatively,a single 12-inch layer <br /> of Type II bedding can be used,except at drop structures. For required bedding thickness,see Table <br /> MD-12. At drop structures.a combination of filter fabric and Type II bedding is acceptable as an <br /> alternative to a two-layer filter. <br /> Table MD-12—Thickness Requirements for Granular Bedding <br /> Minimum Bedding Thickness(inches) <br /> Riprap Designation Fine-Grained Soils. Coarse-Grained Soils" <br /> Type I Type II Type II <br /> VL(d5o=6 in).L(150=9 in) 4 4 6 <br /> M(d5o= 12 in) 4 4 6 <br /> H(d5o=18in) 4 6 8 <br /> VH(dso=24 in) 4 6 8 <br /> May substitute one 12-inch layer of Type II bedding. The substitution of one layer of Type II bedding shall not <br /> be permitted at drop structures. The use of a combination of filter fabric and Type II bedding at drop structures <br /> is acceptable. <br /> ••Fifty percent or more by weight retained on the#40 sieve. <br /> `• Rev.04/2008 MD-67 <br /> Urban Drainage and flood Control District <br /> 4122A.120702 Whetstone Associates♦ <br />