2012-07-03_REVISION - M1984014

• Permit No: M1984014
• IBM Index Class Name: REVISION
• Doc Date: 7/3/2012
• Doc Name: RESPONSE TO ADEQUACY REVIEW #2
• From: COTTER
• To: DRMS
• Type & Sequence: AM1
• Email Name: GRM
• Media Type: D
• Archive: No

JD-8 Mine – Drainage Design Plan 21
Attachment 2
Rip Rap Granular Bedding Specifications (from UDFCD 2011)
DRAINAGE CRITERIA MANUAL (V. 1) MAJOR DRAINAGE
Table MD-11—Gradation for Granular Bedding
U.S. Standard Sieve Size
3 inches
1% inches
% inches
1* inches
*16
*50
*100
*200
Percent Weight by Passing Square-Mash Sieves
Type I CDOT Sect. 703.01
100
95-100
10-30
2-10
0-2
Type II CCOT Sect.
703.09 Class A
90-100
20-90
0-20
0-3
The Type I and Type II bedding specifications shown in Table MD-11 were developed using the T-V filter
(Ilene and the fact that bedding which will protect an underlying non-cohesive soil with a mean grain size
of 0.045 mm will protect anything finer. Since the T-V fitter criterion provides some latitude in establishing
bedding gradations, 11 18 possible to make the Type land Type 11 bedding specifications conform with
Colorado Division of Highways' aggregate specifications. The Type 1 bedding in Table MD-11 is designed
to be the lower toyer in a two-layer filter for protecting fine-grained soils and has a gradation identical to
Colorado Department of Transportation's (CDOT's) concrete sand specification AASHTO M-6 (COOT
Section 703.01). Type II bedding, the upper layer in a two-layer filter, is equivalent to Colorado Division
of Highways' Class A filter material (Section 703.09 Class A) except that it permits a slightly larger
maximum rock fraction. When the channel Is excavated in coarse sand and gravel (50% or more of
coarse sand and gravel retained on the *40 sieve by weight), only tne Type Ilfilter is required.
Otherwise, a two-layer bedding (Type I topped by Type II) is required. Alternatively, a single 12-inch layer
of Type 11 bedding can be used. except at drop struclures. For required bedding thickness, see Table
MD-12. At drop structures, a combination of filler fabric and Type 11 bedding is acceptable as an
alternative to a two-layer filter.
Table MD-12
Rev. 04/2008
Urban Crainaoe and Flood Control District
k
R
for Granular Sodding
Riprap Designation
VL (d 6 in), L. (d5or 9 in)
M (dm = 12 in)
H (dso= 18 in)
VH (doe= 24 in)
Minimum Bedding Thickness (inches)
Fine-Grained Soils
Type 1
4
4
4
4
Type 11
6
6
Coarse-Grained Soils
Type II
6
6
8
8
May substitute one 12-inch layer alt
be permitted at drop shuctures. The use ol e combination of filter fabric and Type 11 beddng at drop strictures
is acceptable.
Fifty percent or more by weight retained on the 8 40 sieve.
&ling. The substitution of one layer of Type II bedding shall not
MD-67
4122A.120702 Whetstone Associates