A well-graded soil must satisfy both the $C_u$ and $C_c$ criteria.

For gravel, a soil is well-graded if $C_u > 4$ and $1 \le C_c \le 3$.

For sand, a soil is well-graded if $C_u > 6$ and $1 \le C_c \le 3$.

$C_c$ is dimensionless.

Helps in identifying gap-graded soils.

Essential parameter for engineering classification of soils.

Does not account for soil plasticity or chemical properties.

Requires full sieve analysis data to calculate.

Filter design in earth dams.

Stability analysis of geotechnical structures.

Classification of soils in the Unified Soil Classification System (USCS).

If $C_c$ falls outside the 1-3 range, the soil is generally considered poorly graded or gap-graded.

Option A ($C_u$) represents the uniformity of particle sizes (range), not the shape of the curve.

Option C ($I_p$) is the Plasticity Index, related to soil consistency (Atterberg limits).