Geology Reference
In-Depth Information
Table 11-3
Soil Classification Chart [2]
Soil Classification
Group
Group
Criteria for Assigning Group Symbols and Group Names Using Laboratory Tests
A
Symbol
Name
B
Coarse-Grained Soils
More than 50%
retained on No. 200
sieve
Gravels
More than 50% of
coarse fraction
retained on No. 4
sieve
Clean Gravels
Less than 5% fines
E
GW
Well-graded gravel
D
C
u
4 and 1
C
c
3
C
GP
Poorly graded gravel
D
C
u
4 and/or 1
C
c
3
C
Gravels with Fines
More than 12% fines
E
GM
Silty gravel
D,F,G
Fines classify as ML or MH
GC
Clayey gravel
D,F,G
Fines classify as CL or CH
Clean Sands
Less than 5% fines
I
SW
Well-graded sand
H
C
u
6 and 1
C
c
3
C
Sands
50% or more of coarse
fraction passes No. 4
sieve
SP
Poorly graded sand
H
C
u
6 and/or 1
C
c
3
C
Sands with Fines
More than 12% fines
I
SM
Silty sand
F, G, H
Fines classify as ML or MH
SC
Clayey sand
F, G, H
Fines classify as CL or CH
Fine-Grained Soils
50% or more passes the
No. 200 sieve
Inorganic
CL
Lean clay
K,L,M
PI
7 and plots on or above “A” line
J
Silts and Clays
Liquid limit less
than 50
ML
Silt
K,L,M
PI
4 or plots below “A” line
J
Organic
Organic clay
K
,
L
,
M
,
N
Organic silt
K
,
L
,
M
,
O
Liquid limit—oven dried
Liquid limit—not dried
0.75
OL
Inorganic
CH
Fat clay
K,L,M
PI plots on or above “A” line
Silts and Clays
Liquid limit 50 or more
MH
Elastic silt
K,L,M
PI plots below “A” line
Organic
Organic clay
K
,
L
,
M
,
P
Organic silt
K
,
L
,
M
,
Q
Liquid limit—oven dried
Liquid limit—not dried
0.75
OH
Highly organic soils
Primarily organic matter, dark in color, and organic odor
PT
Peat
A
Based on the material passing the 3-in. (75-mm)
sieve.
B
If field sample contained cobbles or boulders, or
both, add “with cobbles or boulders, or both” to
group name.
GP-GM, poorly graded gravel with silt
GP-GC, poorly graded gravel with clay
F
If fines classify as CL-ML, use dual symbol
GC-GM or SC-SM.
G
If fines are organic, add “with organic fines” to
group name.
H
If soil contains
15% gravel, add “with gravel”
to group name.
I
Sands with 5 to 12% fines require dual symbols:
SW-SM, well-graded sand with silt
SW-SC, well-graded sand with clay
SP-SM, poorly graded sand with silt
SP-SC, poorly graded sand with clay
J
If Atterberg limits plot in hatched area, soil is a
CL-ML silty clay.
K
If soil contains 15 to 29% plus No. 200, add
“with sand” or “with gravel,” whichever is pre-
dominant.
L
If soil contains
30% plus No. 200, predomi-
nantly sand, add “sandy” to group name.
M
If soil contains
30% plus No. 200, predomi-
nantly gravel, add “gravelly” to group name.
N
PI
4 and plots on or above “A” line.
O
PI
4 or plots below “A” line.
P
PI plots on or above “A” line.
Q
PI plots below “A” line.
(D
30
)
2
D
10
*
D
60
C
C
u
=
D
60
D
10,
C
c
=
D
If soil contains
15% sand, add “with sand” to
group name.
E
Gravels with 5 to 12% fines require dual symbols:
GW-GM, well-graded gravel with silt
GW-GC, well-graded gravel with clay
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