Coarse Soil Classification Based on Curve Parameters
A well-graded grain size distribution is present, if CU ≥ 6 and 1 ≤ CC ≤ 3, whereas a poorly-graded or intermittent grain size distribution holds true for all other cases (table). However, according to [Estermann (1994)], these determinations are to be slightly limited, as both criteria can also hold true for certain discontinuously running grading curves.
Table:
Classification of coarse types of soil depending on the coefficient of uniformity CU and the coefficient of curvature CC according to DIN 18196 [DIN18196:1988]
| Designation | Abbreviation | Coefficient of Uniformity | Coefficient of Curvature |
| Cu | Cc | ||
| Poorly-graded (uniformly graded) | E | < 6 | arbitrary |
| Well-graded | W | ≥ 6 | 1 to 3 |
| Intermittently graded (gap graded) | I | ≥ 6 | < 1 or > 3 |
