Grain Size Distribution and Soil Classification

Material grain size specifications are commonly specified as multiple screen sizes and a range in acceptable percent passing to create a grain size envelope with upper an lower bounds. Not sure what your comment is truly stating regarding the D80-D30, is this the only specification for the material you can show up with a boulder and a lump of clay and hit any specification by adjusting the amount of clay to mix with boulders.

Thank you for the input and feedback. Yes I was not completely sure how to word my concern. Usually Sieve Analysis and material gradations reference the D[sub]60[/sub] particle size and the D[sub]10[/sub] partical size in order to obtain the C[sub]u[/sub] (Coefficient of uniformity) and also the D[sub]30[/sub] is used in a formula for the C[sub]c[/sub] (Coefficient of curvature). So I was surprised to see a specification referencing the D[sub]80[/sub], which in general would be more smaller particles. (Comparing the same soil sample). Therefore my question is what soil properties would this fraction of smaller particle sizes effect. Given a soil description of Silty Sand (USCS designation of SM). Would more smaller particle sizes effect the shrikage factor, I believe it would, aside from this property or behavior, this writer was searching for more definitive reasoning or output.

Again any and all input is appreciated and look forward to summarizing a better conclusion on why this particular specification has referenced the particle size (D[sub]80[/sub]). Thank you for your time.