Soil Classification
Soil Classification
(OP)
When we talk about a soil classified as GW (Graded Well), what does that type of soil really look like? Does that mean it has a broad or narrow spectrum of grain sizes?
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RE: Soil Classification
RE: Soil Classification
RE: Soil Classification
a. the overall material is more than 50% coarser than the #200 sieve size.
b. 50% of the coarse size (i.e., a. above) is gravel sized - retained on #4 sieve or 12.5mm).
c. The percent of fines passing the #200 sieve is less than 5%.
d. The coefficient of uniformity (D60/D10) is greater than 4.
e. The coefficient of curvature ( (D30*D30)/(D60*D10) ) lies between 1 and 3.
For completeness, the material would be called GP if points d. and e. are not met. If more than 12% passes the #200 sieve, the "gravelly" material would be classified as MH or MC depending on where the Atterberg limits fall on the Plasticity chart. If the material has between 5 and 12% fines, then there would be a dual symbol use (GW-GM, GP-GC, etc.)
This is given in almost all soil mechanics books as well as in ASTM.
RE: Soil Classification
One point of correction; if more than 12% passes the #200 sieve, the material is GM or GC - the "M" for silty and "C" for clayey fines (as determined by Atterberg limits).
RE: Soil Classification
RE: Soil Classification
well graded means (in figurative terms) that the curve on the particle size distribution graph is smooth and concave (think of it as a pizza with the lot - there's a bit of everything on it)
the flatter the curve - the broader the spectrum of particle sizes, the steeper the curve (usually with kinks in it) means that the particle sizes are concentrated in a narrow spectrum only... if the spectrum is too narrow, we call it a 'uniform soil'
the term 'well-graded' is a bit subjective as it depends which type of soil youre talking about but the curves on the particle size plot are semi-logs so it makes the comparison of two different types of soils with the same degree of uniformity easy
the opposite of 'well-graded' is 'poorly-graded' and this can be one of two things, 'gap-graded' = the curve has a gap in it indicating that there's probably heaps of fines and heaps of gravels but nothing in between or 'uniform soil' as mention above
hope this helps, albeit late mail
RE: Soil Classification
RE: Soil Classification
I have never been exposed to different log particle size scales because here in Australia, we always use the USCS particle sizes (each chart displays the full spectrum) - thats what makes it easier to compare 'em
but it's useful to be aware that a difference can exist and to be cautious of it - well spotted
RE: Soil Classification
RE: Soil Classification
Also, the opposite of well-graded is poorly sorted, to the geologist, indicating a wide range of grain sizes.
RE: Soil Classification
The opposite of well graded is well sorted, indicating that the majority of the grains are of simular size, i.e. poorly-graded.
Poorly sort means there isa range of grain sizes. The same as well graded.
RE: Soil Classification
RE: Soil Classification
The only question is: was it explained well, poorly, uniformly or just plain-ol' gap-explained...sorry, couldn't resist a little humor after another day at the grind.
Remember: The Chinese ideogram for “crisis” is comprised of the characters for “danger” and “opportunity.”
-Steve
RE: Soil Classification