In: Civil Engineering
Coarse soils are the soil in which 50% or more by weight of the soil particles retained on no. 200 ASTM sieve or 0.0075 mm seive .
Or the 50% or more soil particles have size greater than 0.0075 mm.
The classification of coarse grained soils are as -
Sand and Gravel .
And further well graded sand , poor graded sand , well graded gravel or poor graded gravel.
If 50% of coarse fraction particles passes through No. 4 ASTM sieve then it ais called as sand .
And if more than 50% of coarse fraction retained on No. 4 ASTM sieve it is called as gravel .
And further , if coefficient of uniformity = ( D60/D10) is greater than 6 and coefficient of curvature ( D30/D60 D10) is between 1 to 3 then it is well graded sand .
Otherwise , poor graded sand .
And if Coefficient of uniformity is greater than 4 and coefficient of curvature is between 1 and 3 , it is well graded gravel .
Else poor graded gravel.
.....
If any doubt or more clarification kindly comment. Thank you.