Coefficient of uniformity (cu)

Definition

The coefficient of uniformity (cu) is a numerical measure that describes the gradation of a soil sample, specifically indicating the range of particle sizes within that sample. A higher cu value signifies a greater range of particle sizes, which often suggests that the soil is more well-graded and may have better engineering properties, while a lower cu indicates a more uniformly sized particle distribution. This measure plays a critical role in soil classification and understanding the physical behavior of soils in engineering applications.

5 Must Know Facts For Your Next Test

1. The coefficient of uniformity is calculated using the formula: cu = D60 / D10, where D60 is the particle diameter at which 60% of the sample's weight is finer, and D10 is the diameter at which 10% is finer.
2. A cu value less than 4 typically indicates poorly graded soil, while values greater than 6 suggest well-graded soil.
3. In geotechnical engineering, understanding cu helps predict soil compaction and stability, which are crucial for construction projects.
4. The coefficient of uniformity is part of the Unified Soil Classification System (USCS), which categorizes soils based on their texture and grain size distributions.
5. Soils with high cu values are often preferred in engineering applications as they tend to provide better load-bearing capacities.

Review Questions

• How does the coefficient of uniformity influence the engineering properties of soil?
  • The coefficient of uniformity directly impacts the engineering properties of soil by indicating its gradation. Soils with a higher cu value generally have a wider range of particle sizes, which can lead to better compaction and drainage characteristics. In contrast, soils with low cu values may exhibit poor load-bearing capacity and increased susceptibility to settlement or erosion. Understanding cu helps engineers select appropriate materials for construction and assess their performance under various loading conditions.
• Discuss how the coefficient of uniformity fits into the broader context of soil classification systems.
  • The coefficient of uniformity plays a significant role in soil classification systems such as the Unified Soil Classification System (USCS). It helps categorize soils based on their gradation, which influences their physical behavior and suitability for engineering applications. By incorporating cu into these classification systems, engineers can better assess the potential performance and stability of different soil types. This facilitates informed decision-making regarding site development and construction methods.
• Evaluate the importance of determining the coefficient of uniformity in geotechnical investigations and its implications for construction practices.
  • Determining the coefficient of uniformity is crucial in geotechnical investigations as it provides insights into the particle size distribution within a soil sample. This information is essential for predicting how the soil will behave under load and how it will respond to moisture changes. High cu values can indicate well-graded soils that enhance stability and reduce settlement risks, while low cu values may require additional considerations during construction. Recognizing these factors allows engineers to choose suitable foundation designs and mitigate potential risks associated with inadequate soil properties.

Related terms

Soil gradation: The distribution of different particle sizes in a soil sample, affecting its strength and drainage properties.

Coefficient of permeability: A measure of how easily water can flow through soil, which is influenced by the soil's grain size and arrangement.

Effective stress: The stress carried by the soil skeleton, critical for understanding soil behavior under loading conditions.