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For gravels uniformity coefficient (Cu) should be
1
2
greater than 4
greater than 6
greater than 4
The uniformity coefficient (CuтАЛ) is a measure of particle size distribution in soils. For a gravel to be classified as well-graded, the Indian Standard (IS) Classification system requires CuтАЛ>4, while for sands, CuтАЛ>6 is required.
The uniformity coefficient (CuтАЛ) is a measure of particle size distribution in soils. For a gravel to be classified as well-graded, the Indian Standard (IS) Classification system requires CuтАЛ>4, while for sands, CuтАЛ>6 is required.
CuтАЛ=D10тАЛD60тАЛтАЛ тАФ Definition of the Uniformity Coefficient, where D60тАЛ and D10тАЛ are grain diameters in mm corresponding to 60% and 10% passing, respectively.
The coefficient of uniformity is defined as the ratio of the diameter through which 60% of the soil mass passes (D60тАЛ) to the diameter through which 10% of the soil mass passes (D10тАЛ). A higher CuтАЛ indicates a wider range of particle sizes, which allows smaller particles to fill the voids between larger ones, leading to higher density and better interlocking characteristics in gravels.
Uniformity coefficient is dimensionless.
CuтАЛ=1 represents a perfectly uniform soil (all particles of the same size).
Well-graded gravel (GW) requires CuтАЛ>4 and Coefficient of Curvature (CcтАЛ) between 1 and 3.
Well-graded sand (SW) requires CuтАЛ>6 and CcтАЛ between 1 and 3.
Provides a quantitative measure of soil gradation.
Helps in engineering classification of coarse-grained soils.
Does not account for particle shape.
Insufficient to define soil properties without the Coefficient of Curvature (CcтАЛ).
Design of drainage filters.
Foundation engineering.
Pavement subgrade analysis.
| Feature | Condition | Condition |
|---|---|---|
Material | Gravel | Sand |
Requirement | CuтАЛ>4 | CuтАЛ>6 |
Uniformity Coefficient is also known as the Hazen coefficient.
Option D (CuтАЛ>6) refers to the requirement for well-graded sands, not gravels.
C is correct тАФ For well-graded gravels, the Indian Standard classification requires the uniformity coefficient CuтАЛ to be greater than 4.
Always remember the mnemonic: 'Gravels are more uniform (4) than Sands (6)' when recalling these threshold limits for well-graded soils.
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