Uniformity Coefficient

Uniformity coefficient, abbreviated as \(C_u\), also called coefficient of uniformity, a dimensionless number, classifies a soil as well graded or poorly graded.  It is a measure used in geotechnical and civil engineering to describe the particle size distribution of a granular material such as soil, sand, or gravel.  It is an important parameter in soil mechanics and plays a significant role in various engineering applications, including the design of foundations, embankments, and drainage systems.

Key Points about Uniformity Coefficient

• A higher uniformity coefficient indicates a wider range of particle sizes in the material, suggesting that the material is less uniform in terms of particle size distribution.
• A lower uniformity coefficient indicates a more uniform distribution of particle sizes.

Engineers use the uniformity coefficient to assess the suitability of a granular material for various construction purposes.  Materials with a high CU may have a wide range of particle sizes, which can affect their compaction properties, permeability, and stability in construction projects.  In contrast, materials with a lower CU are often preferred for certain applications because they are more uniform and predictable in their behavior.

 

Uniformity Coefficient Formula
\( C_u \;=\;  \dfrac{ D_{60} }{ D_{10} }\)     (Uniformity Coefficient) \( D_{60} \;=\;   C_u  \cdot  D_{10}   \) \( D_{10} \;=\;  \dfrac{ D_{60} }{ C_u }\)
Symbol	English	Metric
\( C_u \) = uniformity coefficient	\(dimensionless\)	\(dimensionless\)
\( D_{10} \) = is the sieve diameter (grain size) which there are 10% of particles go through.	\(in\)	\(mm\)
\( D_{60} \) = is the sieve diameter (grain size) which there are 60% of particles go through.	\(in\)	\(mm\)