The Coefficient of Uniformity (CU) is an essential parameter in soil mechanics that helps determine the gradation and particle size distribution of a soil sample. It is widely used in geotechnical engineering to assess the suitability of soil for construction and drainage applications.
Formula
The formula to calculate the coefficient of uniformity is:
CU = D60 / D10
Where:
- D60 = Particle diameter at 60% passing
- D10 = Particle diameter at 10% passing
How to Use
- Measure the particle sizes (D60 and D10) from a sieve analysis.
- Input the values in the respective fields.
- Click “Calculate” to get the coefficient of uniformity.
- A higher CU value indicates well-graded soil, while a lower CU suggests poorly graded or uniform soil.
Example
If a soil sample has:
- D60 = 0.5 mm
- D10 = 0.1 mm
Then, CU = 0.5 / 0.1 = 5
A CU value of 5 suggests that the soil is well-graded and suitable for engineering applications.
FAQs
1. What is the coefficient of uniformity?
It is a ratio that indicates the gradation of soil particles, helping engineers classify soil.
2. Why is CU important in soil mechanics?
It determines if a soil sample is well-graded, poorly graded, or uniform, which affects strength, permeability, and compaction.
3. What does a high CU value mean?
A high CU (greater than 6 for sands and 4 for gravels) means the soil contains a wide range of particle sizes, making it well-graded.
4. What does a low CU value mean?
A low CU (close to 1) suggests the soil has uniform particles, meaning it is poorly graded and may have drainage issues.
5. How do I determine D60 and D10?
D60 and D10 are obtained from a sieve analysis graph, representing the particle diameters at 60% and 10% passing.
6. What is a well-graded soil?
Well-graded soil has a good distribution of different-sized particles, improving compaction and stability.
7. What is a poorly graded soil?
Poorly graded soil consists of similar-sized particles, leading to poor compaction and drainage properties.
8. Can CU be used for concrete aggregates?
Yes, CU helps evaluate the gradation of aggregates, ensuring proper mix design for concrete strength.
9. How does CU affect soil permeability?
Soils with low CU (uniform particles) have high permeability, while well-graded soils have lower permeability.
10. What is the typical CU range for construction materials?
- Sands: CU > 6 is well-graded
- Gravels: CU > 4 is well-graded
11. Can CU alone determine soil suitability for construction?
No, it should be used along with coefficient of curvature (CC), Atterberg limits, and soil classification systems.
12. What happens if CU is too high?
Extremely high CU values may indicate too much variation, which could affect soil compaction efficiency.
13. Is CU different for coarse and fine-grained soils?
Yes, CU is primarily used for coarse-grained soils like sands and gravels, not for fine-grained clays.
14. How does CU impact foundation design?
Well-graded soils (higher CU) are preferred for foundations as they provide better load-bearing capacity.
15. How does CU affect soil compaction?
Higher CU values improve compaction by filling voids between larger particles.
16. Can CU be greater than 10?
Yes, in some cases, CU can be high for very well-graded soils, but values above 10 are rare in natural deposits.
17. What happens if CU is too low for a construction site?
Low CU may result in poor soil stability, excessive settling, or high water drainage, making it unsuitable for construction.
18. How do engineers improve CU for a construction site?
By mixing different soil grades, adding stabilizers, or blending coarse and fine particles.
19. Is CU related to soil shear strength?
Yes, well-graded soils with higher CU typically have higher shear strength.
20. Can CU be used in road construction?
Yes, CU is used in highway engineering to assess subgrade and pavement material quality.
Conclusion
The Coefficient of Uniformity Calculator is a valuable tool in geotechnical engineering for classifying soil gradation. A higher CU value suggests better soil stability and compaction properties, making it ideal for construction, roadworks, and drainage systems. Understanding this coefficient helps engineers design more efficient and durable structures.