How to calculate uniformity coefficient in soil?
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Calculating the coefficients of uniformity and curvature requires grain diameters. The grain diameter can be found for each percent of the soil passing a particular sieve. This means that if 40% of the sample is retained on the No. 200 sieve then there is 60% passing the No. 200 sieve.[1]
The coefficient of uniformity, Cu is a crude shape parameter and is calculated using the following equation:
{\displaystyle C_{u}={\frac {D_{60}}{D_{10}}}}
where D60 is the grain diameter at 60% passing, and D10 is the grain diameter at 10% passing
The coefficient of curvature, Cc is a shape parameter and is calculated using the following equation:
{\displaystyle C_{c}={\frac {(D_{30})^{2}}{D_{10}\times \ D_{60}}}}
where D60 is the grain diameter at 60% passing, D30 is the grain diameter at 30% passing, and D10 is the grain diameter at 10% passing
Once the coefficient of uniformity and the coefficient of curvature have been calculated, they must be compared to published gradation criteria.
The coefficient of uniformity, Cu is a crude shape parameter and is calculated using the following equation:
{\displaystyle C_{u}={\frac {D_{60}}{D_{10}}}}
where D60 is the grain diameter at 60% passing, and D10 is the grain diameter at 10% passing
The coefficient of curvature, Cc is a shape parameter and is calculated using the following equation:
{\displaystyle C_{c}={\frac {(D_{30})^{2}}{D_{10}\times \ D_{60}}}}
where D60 is the grain diameter at 60% passing, D30 is the grain diameter at 30% passing, and D10 is the grain diameter at 10% passing
Once the coefficient of uniformity and the coefficient of curvature have been calculated, they must be compared to published gradation criteria.
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