Grading Curve
The graphical representation of sieve analysis is also knows as Grade curve.
1. Readings recorded from sieve analysis is plotted in graph shown below (take particle size on X-axis and percent finer on Y-axis). This graph is also known as Grading Curve.
2. With respect to this graph 10%, 30% and 60% finer, and dimeter from graph is also designated as D10, D30 and D60
3. Calculate the Coefficient of uniformity (Cu)and Coefficient of curvature (Cc) by using following equations,
Cu = D60/ D10
Cc = D230/ (D60 x D10)
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Uniformity Coefficient (Cu):
- · The Uniformity coefficient is express as the ratio of D60 to D10.
- · Where D60 is the value where the particle size of aggregates are 60% finer and 40% are coarser.
- · And D10 is the value where the particle size of aggregates are 10% finer and 90% are coarser.
- · And Cu is calculated as, Cu = D60/ D10
- · If Cu is greater than 4: Soil is classified as well graded
- · If Cu is less than 4: Soil is classified as poorly/unifromly graded
Coefficient of Curvature (Cc):
- · The coefficient of curvature is express of D30, D60 and D10.
- · Where D30 is the value where the particle size of aggregates are 30% finer and 70% are coarser.
- · D60 is the value where the particle size of aggregates are 60% finer and 40% are coarser.
- · And D10 is the value where the particle size of aggregates are 10% finer and 90% are coarser.
- · And Cc is calculated as,
- · If Cc is between 1 to 3: Soil is classified as well graded
- · If Cu and Cc is equal to 1: Soil is classified as single sized soil mass.