Organic Soil Classification

Organic soils are classified as per [ASTM D2487-06] according to the table below.

Table:

Organic soil classification as per [ASTM D2487-06]

Criteria for Assigning Group symbols and Group Names Using Laboratory Tests^A				Group Symbol	Group Name
FINE-GRAINED SOILS	Silts and Clays
50 % or more passes the No. 200 sieve	Liquid limit less than 50	Organic	Liquid limit - oven dried < 0.75	OL	Organic clayK,L,M,N
	Liquid limit less than 50		Liquid limit - oven dried < 0.75	OL	Organic siltK,L,M,O
	Liquid limit 50 or more		Liquid limit - oven dried < 0.75	OH	Organic clayK,L,M,P
	Liquid limit 50 or more		Liquid limit - oven dried < 0.75	OH	Organic siltK,L,M,Q
HIGHLY ORGANIC SOILS	Primarily organic matter, dark in color, and organic odor			PT	Peat

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

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