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EM 1110-2-2300
31 Jul 94

f. To ensure sufficient permeability, set the mini-
Table B-1
Categories of Base Soil Materials mum D 15 greater than or equal to 3 to 5 × maximum d 15
of the base soil before regrading, but no less than
Percent finer than the No. 200
0.1 mm.
Category (0.075 mm) sieve
1 85 g. Set the maximum particle size at 3 in. (75 mm)
2 40-85
3 15-39 and the maximum passing the No. 200 (0.075 mm) sieve
4 15 at 5 percent. The portion of the filter material passing the
No. 40 (0.425 mm) sieve must have plasticity index (PI)
of zero when tested in accordance with EM 1110-2-1906.
e. Determine the maximum D size for the filter in
15
accordance with Table B-2. Note that the maximum D 15 h. Design the filter limits within the maximum and
is not required to be smaller than 0.20 mm. minimum values determined in steps e, f, and g. Standard
gradations may be used if desired. Plot the limit values
and connect all the minimum and maximum points with
straight lines. To minimize segregation and related
Table B-2
Criteria for Filters effects, filters should have relatively uniform grain-size
distribution curves, without “gap grading”--sharp breaks in
Base Base soil description, and Filter criteria in
curvature indicating absence of certain particle sizes.
soil percent finer than No. 200 terms of maximum
category (0.075 mm) sieve 1 D 15 size 2 Note This may require setting limits that reduce the broadness
of filters within the maximum and minimum values deter-
1 Fine silts and clays; D 15 < 9xd 85 (1)
more than 85% finer mined. Sand filters with D 90 less than about 20 mm
generally do not need limitations on filter broadness to
2 Sands, silts, clays, D 15 < 0.7 mm prevent segregation. For coarser filters and gravel zones
and silty and clayey that serve both as filters and drains, the ratio D /D
sands; 40 to 85% finer. 90 10
should decrease rapidly with increasing D 10 size. The
40-A limits in Table B-3 are suggested for preventing segrega-
3 Silty and clayey D 15 < (2),(3)
40-15
sands and gravels; tion during construction of these coarser filters.
15 to 39% finer {(4 x d 85 )- 0.7 mm}
+ 0.7 mm
Table B-3
4 Sands and gravels; less D 15 < 4to5xd 85 (4) D 10 and D 90 Limits for Preventing Segregation
than 15% finer.
If minimum D 10 Then maximum D 90
mm mm
1
Category designation for soil containing particles larger than
4.75 mm is determined from a gradation curve of the base soil <0.5 20
which has been adjusted to 100% passing the No. 4 (4.75 mm) .5 - 1.0 25
sieve. 1.0 - 2.0 30
2 2.0 - 5.0 40
Filters are to have a maximum particle size of 3 in. (75 mm) and
a maximum of 5% passing the No. 200 (0.075 mm) sieve with the 5.0-10 50
plasticity index (PI) of the fines equal to zero. PI is determined on 10-50 60
the material passing the No. 40 (0.425 mm) sieve in accordance
with EM 1110-2-1906. To ensure sufficient permeability, filters are
to have a D 15 size equal to or greater than 4 x d 15 but no smaller
than 0.1 mm. B-3. Permeability

NOTES: (1) When9xd 85 is less than 0.2 mm, use 0.2 mm. The requirement that seepage move more quickly through
(2) A = percent passing the No. 200 (0.075 mm) sieve the filter than through the protected soil (called the per-
after any regrading.
meability criterion) is again met by a grain-size relation-
(3) When4xd 85 is less than 0.7 mm, use 0.7 mm.
(4) In category 4, the d 85 can be based on the total base ship criterion based on experience:
soil before regrading. In category 4, the D 15 < 4x
d 85 criterion should be used in the case of filters Permeability
beneath riprap subject to wave action and drains
which may be subject to violent surging and/or
vibration. 15 percent size of filter material > 3 to 5 (B-1)
15 percent size of protected soil

B-2