Coefficients of Uniformity and Curvature

Understanding Uniformity Coefficient and Curvature Coefficient

Soil gradation is a classification system used to determine the particle size distribution of soil. It is an important aspect of geotechnical engineering as it is an indicator of various engineering properties, such as hydraulic conductivity, shear strength, and compressibility.

Soil gradation is classified into two main categories, coarse-grained soils, and fine-grained soils. Coarse-grained soils, which include gravels and sands, are graded as either well-graded or poorly graded. Poorly graded soils are further classified into two subcategories: uniformly-graded and gap-graded soils. Fine-grained soils, which include silts and clays, are classified based on their Atterberg limits.

The process of grading a soil involves collecting data, calculating the coefficients of uniformity and curvature, and grading the soil based on the grading criteria given in the Unified Soil Classification System or the AASHTO Soil Classification System. Soil gradation is determined by analyzing the results of either a sieve analysis or a hydrometer analysis.

Uniformity Coefficient Calcultaion

Cu = D60 / D10

Coefficient Curvature Calculation

Cc = (D30)2 / D10 x D60

Calculating the coefficients of uniformity and curvature requires determining grain diameters. The coefficient of uniformity is a crude shape parameter and the coefficient of curvature is a shape parameter. Once these coefficients have been calculated, they are compared to published gradation criteria.

Soil gradation is essential in geotechnical engineering, as the gradation of in situ or on-site soil often controls the design and ground water drainage of a site. For instance, a poorly graded soil will have better drainage than a well-graded soil because of the larger void spaces present in a poorly graded soil. The soil gradation is also considered when selecting fill material for projects like highway embankments and earthen dams since a well-graded soil is more easily compacted than a poorly graded one.

In conclusion, soil gradation plays an important role in geotechnical engineering as it provides vital information about a soil's characteristics, which can affect various engineering properties of the soil. Therefore, it is important to accurately grade soils and make use of this information when designing projects.