UFC 3-270-04
15 March 2001
d15 percent passing size of filter material
<5
d85 percent passing size of material being drained
and
d50 percent passing size of filter material
< 25
d50 percent passing size of material being drained
The criteria should be used when protecting all soils, except that for nondispersive lean clay (CL)
or fat clay (CH) soils without sand or silt particles, the 50 percent size relationship can be
disregarded.
It is essential that the filter be well graded and have a coefficient of uniformity of not more than
20. The coefficient of uniformity is:
d60 percent passing size of filter material
d10 percent passing size of filter material
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