Table 6.7. Sizes of Materials.
Base Material (Sand)
Riprap (Rock)
D85 = 1.5 mm
D85 = 400 mm
D50 = 0.5 mm
D50 = 200 mm
D15 = 0.17 mm
D15 = 100 mm
The riprap does not contain sufficient fines to act as the filter because
D15 (Riprap) 100
=
= 600
D15 (Base)
0.17
which is much greater than 40, the recommended upper limit (requirement 6.25). Also
D15 (Riprap) 100
=
= 67
D85 (Base)
1.5
which is much greater than 5, the recommended upper limit (requirement 6.26).
The properties of the filter to be placed adjacent to the base are as follows:
D50 (Filter )
< 40
(1)
D50 (Base)
D50 (Filter) < (40) (0.5) = 20 mm
so
D15 (Filter )
< 40
(2)
D15 (Base)
D15 (Filter) < (40) (0.17) = 6.8 mm
so
D15 (Filter )
<5
(3)
D85 (Base)
D15 (Filter) < (5) (1.5) = 7.5 mm
so
D15 (Filter )
>5
(4)
D15 (Base)
D15 (Filter) > (5) (.17) = 0.85 mm
so
Thus, with respect to the base
0.85 mm < D15 (Filter) < 6.8 mm
6.72
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