Question

Explain the importance of coefficient of uniformity and coefficient of curvature.

Answer 1

Coefficient of uniformity- It is one of the parameter used for gradation curve which is obtained by the process of sieve analysis. It is used to determine the gradation os soil as well graded or poorly graded and the expression is related as follows -  

  

The terms defined here as Cu is uniformity coefficient where D60 is grain diameter below which 60% of particles pass and D 10 is grain diameter below which 10% of particles pass.

Lower value of Cu means a uniform soil where as if the value is 1 it means the soil particularly contains of one soil particle size.

Coefficient of curvature - It is the parameter used for the gradation of soil during sieve analysis. It is used to classify the soil as poorly graded or well graded using the relation below -

Here Cc is the coefficient of curvature and D60 is grain diameter below which 60% of particles pass and D30 is grain diameter below which 30% of particles pass and D10 is grain diameter below which 10% of particles pass

When the value is between 1 and 3 the soil is said to be well graded.

Gradation is very important in soil mechanics as various properties like the shear strength , bearing capacity , consolidation , drainage depends on these parameters.