In the Coefficient of Curvature (Cc), what formula is used to determine its value?

The Coefficient of Curvature (Cc) is a key parameter used in geotechnical engineering to assess the gradation or distribution of particle sizes in soil. The correct formula for calculating Cc is derived from the effective diameters of the soil particles at specified percentiles. The correct relationship is expressed as:

Cc = (D30^2) / (D10 * D60)

where:

• D10, D30, and D60 correspond to the particle diameters at the 10th, 30th, and 60th percentiles of particle size distribution, respectively.

This formula measures the degree of uniformity of the soil. A Cc value of approximately 1 indicates a well-graded soil, whereas values significantly deviating from 1 suggest a poorly graded or gap-graded soil.

The options presented do not align correctly with the standard definition used in the field for Cc, with the correct formulation clearly expressing that D30 is squared. The other choices present different ratios and combinations of particle sizes that do not adhere to the conventional definition and thus do not accurately represent the Coefficient of Curvature. Understanding this relationship helps engineers evaluate soil stability, permeability, and suitable applications in construction and civil engineering projects.