* 0 = ~log2 d (mm)
Wentworth Scale
Phi Units
0
Grain
Diameter
U.S. Standard
Sieve Size
Unified Soil
Classification
(Size Description)
d (mm)
(USC)
...
Boulder
-8
256
Lobble
Cobble
76.2
64.0
3 in.
-6
Coarse
%in.
Gravel
19.0
Pebble
Fine
4.76
4.0
2.0
1.0
0.5
No. 4
Coarse
Granule
i
No. 10
Very Coarse
—1
Coarse
0
Medium
Sand
Medium
1
No. 40
0.42
0.25
Sand
Fine
2
Fine
3
0.125
Very Fine
0.074
No. 200
Sût
4
0.0625
CLay
8
0.00391
Silt or Clay
Colloid
12
0.00024
Figure 4-7. Grain Size Scales (Soil Classification)
4-14