Cohesive Soil Classification

The following table presents classification of cohesive soils for engineering purposes based on particle size, coefficient of uniformity (Cu) and coefficient of curvature (Cc) [ASTM D2487-06]. Cohesive soils do not crumble, are hard to break up when dry and include clayey silts, sandy clays, silty clays, and clays.

Table:

Cohesive soil classification table as per [ASTM D2487-06]

Criteria for Assigning Group symbols and Group Names Using Laboratory TestsA				Soil Group Symbol	Soil Group Name
FINE-GRAINED SOILS	Silts and Clays	Inorganic	PI > 7 and plots on or above "A" lineJ	CL	Lean clayK,L,M
50 % or more passes the No. 200 sieve	Liquid limit less than 50		PI < 4 or plots below "A" lineJ	ML	SiltK,L,M
		Organic	Liquid limit - oven dried < 0.75	OL	Organic clayK,L,M,N
			Liquid limit - not dried	OL	Organic siltK,L,M,O
	Silts and Clays	Inorganic	PI plots on or above "A" line	CH	Fat clayK,L,M
	Liquid limit 50 or more		PI plots below "A" line	MH	Elastic siltK,L,M
		Organic	Liquid limit - oven dried < 0.75	OH	Organic clayK,L,M,P
			Liquid limit - not dried		Organic siltK,L,M,Q

ABased on the material passing the 3-in. (75-mm) sieve

JIf Atterberg limits plot in hatched area, soil is a CL-ML, silty clay.

KIf soil contains 15 to 29 % plus No. 200, add "with sand" or "with gravel", whichever is predominant.

LIf soil contains ≥ 30 % plus No. 200, predominantly sand, add "sand" to group name.

MIf soil contains ≥ 30 % plus No. 200, predominantly gravel, add "gravelly" to group name.

NPI ≥ 4 and plots on or above "A" line

OPI < 4 or plots below "A" line

PPI plots on or above "A" line

QPI plots below "A" line