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TECHNICAL MEMORANDUM NO. 3357 /'.
-
I
THE UNIFIED SOlL CLASSIFICATION SYSTEM
APPENDIX A
CHARACTERISTICS OF SOlL GROUPS PERTAINING TO
EMBANKMENTS AND FOUNDATIONS
APPENDIX B
CHARACTERISTICS OF SOlL GROUPS PERTAINING TO
ROADS AND AIRFIELDS
am~r.umc v~e*a.un.. u~am
Office, Chief OF Engine* \ .-
U. S. Army
Conducted by
. .', '
.I
U. S, Army Engineer Waterways Expriment Station
CORPS OF ENGINEERS
Vicksburg, Mirsirrippi
DISTRIBUTION OF THIS DOCUMENT IS UNLIMITED
b

Preface
The purpoee of this mat~ual ie to deecribe md explain the use of
the "Unified Soil Claeeif ication System" in order that ideatif icatlon
of soil types will be on a cmon basis throughout the agancies uing
this rystam.
The program of military airfield construction undertaken by the
Department of the Army in 1941 revealed at ul early eta- that existing
soil claseificatione were not entirely applicable to the work in~lved.
In 1942 the Corps of Engineero tentatively adopted the "Airfield
Classification" of roile vhich had been developed by R, ArthUr
Casagrsnds of the Harvard Univerrity Oradute School of Enelmering,
Ae a result of experience gained since that time, the origlml claesi-
fication has bean expanded and reviwd in cooperation with the Bure6u
of Rec~tion so tlmt it appliea not only to airfialbs but mlro to
embankmerite, founbatione, and other engineering features.
Acknowbdgamt is made t,o Dr. Arthur Casagrandh, Proferror of
Soil P!chanics and Foundation Engineering, Aarvard Univereity, fcr
permiseion to incorporate in this manual coneiderable information fran
the paper "Classification and Identification of Sollr " publirhed In
Traneactione, American Society of Civil Engineers, volume 113, 1948.
This manualwae preaared under the direction of the Office, Chief of
Engineera, by the Soils Division, Waterways Exptriwnt Station,

Contents
Preface. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . i
Introduction . . . . . . . . . . . . . . . . . , . . . . . . . . . 1
The Claeeification Syetem . . . . . . . . , . . . . . . . . . . . . 4
Discussion of Coarse-grained Soils . . . . . . . . . . . . . . . . 6
Diecueeicn of Fine-grained Soils . . . , . . . . . . . . . . . . . 8
Diacuaeion of Highly Organic Soils . . . . . . . . . . . . . . . . 10
Identification of Soil Croups . . . . . . . . . . . . . . . . . . . 10
General Identification . . . . . . . . , . . . . . . . . . . . . . 11
Laboratory Identification . . . . . . . . . . . . . . . . . . . . . 18
Expaneion of Claesification . . . . . . . . . . . . . . . . . . . . 27
Deecriptive Soil Claesiiication . . . . , . . . . . . . . . . . . 28
Tahles 1-2
Plates 1-9
iii

Need for a classification system
UNIFIED SOIL CLASSIFICATION SYSTEM
Introduction
1. The adoption of the principles of soil mechanics by the engi-
neering profeasion has inspired nmerous attempts tc devise a simple
classification system that will tell the engineer the properties of a
given soil. As a consequence, many classifications have come into exist-
ence based 9n certain properties of soils such as texture, plasticity,
strength, and other ckaracteristico. A few classification systems have
gained fairly wide acceptance, but it is saldom that any particular sya-
ten has provided the ccniplete informstion on r eoil that the engineer
neede. Nearly every engineer who practice6 eoil mechanics will ~ dd
judgment and personal experience as modif iers to whatever soil clascrifi-
-
cation system he uses, so that it may be said that there ate as many
classification systems as there are engineers using them. Obviouely,
within a eiven agency, where designs and plans are reviewed by persons
entirely removed frcm a project, a common basis of sol classification is
necessary so that when an engineer classifies a soil 3s a certain type,
thir; classification will convey to another engineer not familiar with the
region the proper characteristics and behavior of the material. Further
than this, the classification should reflect those behavior characterts-
tics of the soil that are pertinent to the project under consideration.
Basis of the unified soil
claesificaticn system
2. The unified soil claseification system is based on the

identification of soilo according to their textural and plasticity qua~i-
ties and on their grouping wlth respect to behavior. So4.1s seldom exist in
nature separately as sand, gravel, or any other single component, but
are usually found as mixtures with varying proportions of particles of
different sizes; each component part contributes its characteristico to
the soil mixture. The unified soil clasoiiication sy6tem is based on
thoee characterietic~ of the soil that indicate haw it will behave as an
engineering construction material. The following properties have been
found moot useful for this purpose and fom the basis of soil iGentifica-
tion. They can be determined by simple tests and wi-h experience can be
estimated with same accuracy.
. Percentages of gravel, sand, anO fines (fraction passing
No. 200 sieve).
2.
-
Shape of the grain-size-distribution curve.
c, Plasticity and cmpressibility characteristics.
in the ~ulified soil claseification system the soil is given a descriptive
name and a letter symbol indicating its principal character!stjcs.
Purpose and scope of manual
3. It is the purpose of this manual to describe the various soil
groups in detail and to discuss the methods of identification ic order
that a uniform classification prwadure may be followed by all who use
the system. Placement of the soils into their respective groups ir
accomplished by visual examination and laboratory tests ~s a reans cf
basic identificaticr.. This proced~re is described in the ~ain text of
this rcanual. The clascification of tbe aoilt; in rhese Groups acc~rdinr-.
to their engineering behavior for various types of constraction, :iuch as

embanhents, foundaticnc, roads, and airfields, i~ treated separately in
ap~endite~ hereto which will be issued as the need arises. It is rec-
ognized that the unified clacsification system in its present form nay
not prove entirely adequate in all cases, However, it is intended that
the classification of soils in accordance with this eyetem have some de-
gree of elasticity, and that the oystett not be foilowed blindly nor re-
gardec! 8s conipletely rigid.
- Defial.tions of soil comconents
4. Before soils can be cl.assif ied properly in any eyoterr,, includ-
ing the one pre;eated in this manual, it is necessary to establish a
bocic tcrmlnology for the various soil components and to define the terms
11.sed. In the unified oil c!.acsification the names "cobbles," "gravel,"
"canC," and "fines (silt or clay)" are ueed to designate the size ranges
of soil particles. The gravel and sand rangee arc f'wther subdivided
into the groups presented below. The limiting boundariee between the
vnrious r,ize rangen have been wbjtrarily set at certain U. S. Standard
sieve sizes ! n accordance vith the following tabulation:
Component -
Cobbles
Size Range
Above 3 in.
Gravel
Coar-e gravel
Fine gravel
Sand
Coarse sand
Medium sack
Fine sand
Fines (silt or clay)
3 in. to No. 4 (4.76 mm)
3 in. to 3/4 in.
3/4 in. to No. 4 (h.76 mm)
No. 4 (4.76 mm) to No. ,100 (0.074 mm)
No. 4 (4.76 m) to No. 10 (2.0 rnrr,)
No. 10 (2.0 nun) to No. 40 (0.42 nun)
No. 40 (0.42 m) cu Kc. XX) (0.074 mm)
Below KO. 200 (0.074 mm)
These ranges are shobn graphically on the grain-size sheet, plate 1. In

the finest soil component (below No. 200 sieve) the terns "silt" and
"clay" are used respectively to dietlnguish materials exhibiting lower
plasticity from those with higher plasticity. The minus No. 200 sieve
material is "silt" if the liquid limit and plasticity index plot below
the "A!' line on the plasticity chart (plate 2), and la "clay" if tht
liquid limit and plasticity index plot above the "A" line on the chart
(all Atterberg limits tests based on minus No, )+O sieve fraction of a
soil), The foregoing definition holds for inorganic silts and clays
and for orgenic silts, but is not valid for organic ciays since these
latter soils plot below the "A" line, The names of the basic soil com-
ponents can be used as nouns or adJectivee in the nme of a soil., a6
explained later.
The Claseification System
5. A short discussion of the unified aoil classiflcati~n sheet,
table 1, is presented in order that the succeeding detailed description
may be more easily understood. This sheet is designed to apply gener-
ally to the identification of soils ~egardless of the intended engineer-
ing uses. The first three columns of the classification sheet show the
mador divisions of the classification and the group symbols that distin-
buieh the indiyidual soil types. Names of typical and representative
soil types found in each group are shown in column 4. The field proce-
dures for identifying soils by general characteristics and from perti-
nent tests and visual observations are shown in column 5. The desired
descriptive information for a complete identification of a soil is pre-
sented in column 6. In column 7 are presented the laboratory
I

.
classif ication criteria by which the various soil groups are identified
and distinguiehed. Table 2 shows an awiliury echematic method of clas-
sifying soils frcm the results of laboratory tests. The application and
use of thie chart arb diecussed in peater detail under a eubsepuent
heading in this manual.
Soil groups and group aymbois
6. Major divisione. Soils are pimarily divided into coarae-
grained soils, fine-grained soile, and hi~hly organic soils. On a
textural basis, coarse-grained soils art those th&t have 50 per cent or
less of the constituent material passing the No. 2'00 sieve, and fine-
grained 8011s are thcse that have more than 50 per cent passing the
No. 200 sieve. Highly organic soils are in general readily identified
by visual examination. The coarse-grained eoils are eubdivided into
gravel and gravelly soile (symbol o), ~nd sands and sandy soils (sym-
bol s). Fine-grained eoils are subdivided on the basis of the liquid
limit; symbol '. is used for soile with liquid lihlts of 50 and lese,
and syabol H for soils with liquid lhits in excess of 50 (see plate 2).
Peat and other highly orjanic soils are deeignatec? by the symbol Pt and
are not subdivided.
7. Subdivisions, coaree-grained eoils. In general practice there
is no clear-cut boundary between gravelly 8011s and sandy soils, and aa
far ae behavior is concerhed the exact point of division is relatively un-
important. For purposes of identification, coarse-grained soils are
claseed as gravel6 (O) if the areater percentBge of the coarse fraction
(retained on No. 2C0 sieve) is larger than the No. 4 sieve and as sands
(3) if the greater portion of the coarse fraction is finer than the Ro. 4

oieve. Borderline cases may be claesified 86 belonging to both groups,
The gravel (G) and sand (s) groups are each divided into four secondary
groups as follows:
- a, Well-gradec! material with little or no fines. Symbol K.
Groups GW sad SW,
b, Poorly-graded material with little or no fines. Symbol P.
- Groups GP and SP.
t , Coarse material with nonplestic fines or fines wit,h low
- plasticity. Symbol Me Croups GM and SM.
d. Coarse material with plastic fines. Symbol C. Groups .;C
- and SC.
8 Subdivisions, f ine-grained boilo . The f ine-grained soils are
subdivided into groups based on whether they have a relatively low (L)
or high (H) liquid lknit. These two groups are further subdivided a6
follows :
. Inorganic silts and very fine sandy soils; silty or clayey
f iile eands; micaceous and diatoInace0~~ soils; ela.stic
silts. Symbol M, Groups ML and Mi.
-
b, Inorganic clays. Symbol C, Groups CL and CH.
-
GVI and SW moupo
c, Grga1.i~ tilts and clays, Symbol 0. Croups OL and CH.
Diocussion of Coarse-grained Soils
9. These groups ccmprise well-graded gravelly and sandy soils
huvinc little or no nonplaetic fines (leas than 5 per cent paosing the
No. 200 oieve) , The presence of the fines nust not rloticeably change
the strength characteristic^ uf the coarae-grained fraction and must not
interfere with its free-draining charecterictico. If the materla? ,:on-
tainfi less than ', per cent fineti tha: exhlbl t plar:tici%y, thi:

Information should be evaluated and the soil claseifiea as discussed sub-
sequently under "Laboratory Identification. " In areas subJect to frost
action, the msterial should not contain more than trbaut 3 per cent of
soil grains smaller then 0.02 mm in size. Typical examples of GW and St1
soils are sham on plate 3.
GP and SP groups
10. Poorly-graded gravels and sands containing little or no non-
plastic fines (less than 5 per cent passing the No. 200 sieve) are
classed in the GP and SP groups. The materials may be classed as uniform
gravels, uniform sands, or nonuniform mixtures of very coarse mater!al
and very fine sand, with intermediate sizes lacking (sometimes called
skip-graded, gap-graded, or step-graded) , The latter group of ten results
from borrow excavation in which gravel and sand layers are mixed. If the
fine fraction exhibits plasticity, this information should be evaluated
snd the soil classified as discussed subsequently under "Laboratory
Identification." Typical examples of various types of CP and SP soils
are shown on plate 4.
GM end SX urouE
11. ill general, the Gi4 and SM groups comprise grtlvels or sands with
fine6 (more than 12, per cent passing the No. SO0 sieve) having low or no
plasticity, The pla~ticity ?ndex and liquid limit (based on minus No. 40
sieve fraction) of soils :r the moup should plot below the "A" line on
* In the preceding two peragaphs soils of the CV, GF, 211, and SP
groups were defined as having less tb~n 5 per cent passing the Yc. 200
sieve. Soils which have between :, and 12 Fer cent pocsinc the Nc. 2CO
sieve are classed as "bcrderline" and Rre disrusser! in paral;ro~h Sj
under that headinf:.

the plesticity chart. The gradation of the mat:rials is not coneidered
significant and both well- and poorly-graded materials are included.
Some cf the sands and gravels in this group rill have a binder ccmpoaed
of natural cementing agents, so proportione& thct the mixture shows neg-
ligible owelling or shrinkage. Thus the dry strength of such materials
in provided by a small amount of soil binder or by cementation of cal- l
careous material or iron oxide. The fine fraction of other material8
in the GM and SM groups may be composed of silts or rock flour types
having little or no plasticity and the mixture wili exhibit no dry
strength. Typical examples of types of (31 and SM soils are shown on
plate 5.
GC and SC aroups
12. In general, the GC and SC ~'roups comprise gravelly or sandy
6311s with fines (more than 12 per cent passing the No. 200 sieve) which
have either low or hi@ plasticity. The plasticity index and liquid
limit of soils (fraction passing the No. 40 sieve) in the group should
plot above the "A" line on the ~lanticity chart. The gradation of the
materials is not considered significant and both well- and poorly-graded
materials are included. The plasticity of the binder fraction has more
influence on ihe behavior of the soils than dceo variation in Gradation.
The fine fraction is ger.era1.l~ ccrnposed of clays. Typical examples of
GC and OC soils are shown on piate 6.
i,L nrhd biH tlIrOUpS
Discussion uf :, .ne-uralned Soils
13. 1% these j,o,:pr the s:mhol 11 !,us kcen use& to designate
I

predminantly silty material8 and micaceous or diatomaceous soils. The
symbols L and H represent low end high liquid limits, respectively, and
an arbitrary dividing line between the 4x0 is set at a liquid limit of
50. 7be eoils in the ML and ME groupe are sandy silts, clayey silts,
or inorganic silts with relatively low plaet! qity. Also included are
loess-type soils and rock flours, Micaceow ar.d diatomaceo;?s ooile
generally fall within the MEi group but may extend into the ML poup
when their liquid limit 18 lee8 than 50. The same 18 true for certain
types of kaolin clays and some illite clays having relatively low plas-
ticity. Typical examples of soils in the ML and MH gfoups we shown
on plate 7.
-- CL and CH groups
14. In these groups the symbol C stands for clay, with L and H
denotity low or high liquid llmit. The soils are primarily inorganic
clays, Low ~lasticity clays are classified e~s CL and are usually lean
clays, sandy clays, or ellty clap. The medim and high plasticity
clays are claeeified as CH. The~e include the fat chys, gumbo cluys,
certain volcanic clays, and bentonite. The glacial clays of the northern
United States cover a wide band in the CL and CH groups. Typical exam-
ples of eoils in these groups ara shown on plate 8.
OL d aB Rroupe
15. The soils In the OL and OH groups are characterized by the
presence of orgmic matter, hence the symbol 0. Organic silts and chya
are claaeified in Wee groups. The materials have a plasticity range
that cornsponds vith the ML and EQI groups. Typical exllmples of OL and
OH moils are presented on plate 9.

Pt Rrou'D
biscue~ion of Highly Organic Soils
16. The highly organic soils ueually are very compressible and
have undesirable construction characteristics , They are not subdivided
and me cla~sif led into one group wlth the symbol Pti. Peat, humU0, and ;
I 3
swamp soils with a. highly organic texture are typical solls of the
group, Particles of leaves, grass, branches, or other fibroas vegetable
matter are common components of these soils,
Idrntification of Soil Groups
17, The unified soil claosification is so arranged that most soils
may be claeeified into at least the three primary groups (coarse grained,
fine grained, mid highly orgtmic) by means of visual examination and
almple field tests. Classification into the eubdivision8 can also be
made by visual examination with some degree of success, More positive
identification may be made by means of laboratory testa on the materials,
However, in many instances a tentative classification Oetermined in the
field is of great benefit and may be all the ident:fication that is
necessary, depending on the purposes for which the soils in question are
to be used, Methods of general identification of soils are discussed
111 the following paragraphs, and a laboratory testing procedure is pre-
sented. It is emphasized that the two methods of identification are
never entirely separated, Certain characteristics can only be estimated
by visual examination, and in borderline cases it nay be necessary to
verify the classification by laboratory tests. Conversely, the field
!
1
i i d
i 5

I methods are entirely practical for prelirniasry laboratory identification
t
and may be used to avant- in grouping soile in such a manner that I
only s minimum nwnber of laboratory tarts need be run.
Oemral IQntification
. Iho cariest way of burning field identification of eoile is
under the guidance of experienced personnel. Without such asaiatance,
field idantification may be learned by systuaatically camparing the
numsrical bet results for typical soile in each group with the "feel"
of the material while field idtntification procedure8 are being performed.
Coarae-mined eoile
19. Texture and composition. In field identification or coarse-
grained materials a dry sample is spread on a flat eurface and exnmined
to &tormine gradation, grain size and shape, and miueral composition.
Coneiderable experience is required to differentiate, on the basis of
a visual examination, between well-graded and poorly-graded soils.
The durability of the grains of a coaree-grained 8011 may require e.
careful emmination, depending on the use to which the soil is to be
put. Pebbles and sand grains consisting of sound rock are easily iden-
tified. Weathered material is recognized from it8 discolorations and
the mlntive ease with which the grain$ can be crushed. Oravele con-
sisting of weathered granitic rocks, quartzite, etc., are not neceorar-
ily objectio~ble far construction purpoees. On the other hand, coarse-
grained eoile containing frawents of shaley rock may be uneuitable be-
cauee alternate wetting and drying may mrult in their partial or corn-
i
pleta dishtegration. Thie property can be identified by a slaklrr~~ test.
!
i
I
I
I
!
j
I
I

The particles are first thoroughly oven- or sun-dried, then submerged
in water for at least 24 hours, and finally their strength ir teeteb
and compared with the original strength. Some type of ehalee will ccm-
pletely disintegrate when subjected to such a elaking test.
20, Examination of fine fraction* Reference to the identification
sheet (table 1) shove that classification criteria of the various cwse-
grained aoil group6 are based on the amount of material gassing the No,
200 sieve and the plasticity characteristics of the binder fraction
(passing the No, 40 sieve). Various methods may be used to errtimate the
percentage of material parsing the No. 200 sieve; the choice of method
will depend on the skill of the technician, the equipment at hand, and
the time available. One method, decantation, conelete of mixing the
soil w ith water in a suitable container and pouring off the turbid mix-
ture of water and fine soil; succeesive decantations will remove prac-
tically all of the fines and leave only the sand and gravel sizes in the
container, A visual comparison of the residue with the original material
will give some idea of the amount of fines present. Another useful meth-
od is to put a mixture of soil and water in a test tube, shake it thor-
oughly, and allow the mixture to settle. The coarse particles will fall
to the bottom and successively finer particlee will be deposited with
increasing time; the sand sizes will fell out of suspension in 20 to 30
seconds. If the assumption is made that the soil weight is proportional
to its volume, this method may be used to estimate the amount of fines
present. A rough estimate of the amount of fines may be made by spread-
ing the sample out on a level surface trnd making a visual estimate of
the percentage of fine particles present. The presence oi fine sand can

usually be detectbd by rubbing a sample between the fingers; silt or clay
purticlss feel emaoth and stain the fingcrr, whereas the sand feel8 gritty
and does not leave a stain. The "teeth test" is sarmstimse used for this
purpose, and coneiats of bitin# a portion of tho 8crmpJ.e between the
teeth. Sand feels gritty whereas silt .and clay do not; clay tends to
stick to the teeth .hilo eilt dous not. If there appears to be more
than about 12 per cent of thc material passing the No, 200 sieve, the
ample should be separated a8 well as possible by hand, or by decante-
tion end evaporation, removing all of the gravel and coarse eand, and
the characteristics of the fine fraction determined. The binder Is
mixed Kith water and its dry strength and plaeticity characteristics are
exemined. Criteria for dry strength are shown in column 5 of the clas-
sification sheet, table 1; e-~aluation of soile according to dry strength
and plasticity criteria is discussed in succeeding paragraphs in connac-
tion with fine-gained soils. Identificetion of active cementing agents
I
I i
,
!
other than clay usually is not possible by visual and manual examination,
since such agents may require a curing period-of days or even weeks. In !
the absence of such experience the aoils should be claesified tentatively
I
into their apparent groups, neglecting any possible developent of ! i
strength because of cementation.
Fine-mained soils
21. The principal pr0ceC.u-es for field identification of fine-
grained aoils are t:w test for dilatancy (reaction to shaking), the
examination of plasticity chb'acteristics, and the determination of dry
strength. In addition, observations of color and odor are of value,
particularly for organic ooils, Descriptions of the field identification 4

procedures are presented in the follwing paragraphe. The dilatancy,
plasticity, and dry styength tests are performed on the fraction of the
soil finer than the No. 40 sieve. Separation. of particles coar3er than
the No. 40 sieve is clone most expediently in the field by hand. However,
separation by hand probably w ill be most effective for particles coarser
than the No. 10 sieve. Some effort should be made to remove the No. 10
to No. 40 fraction but it is believed that any partf cles in thie size
range remaining after hand separation would haw little effect on the
field identification procedures.
22. Dilatancy. The soil is prepnred for test by removing particles
larger than about the No. 40 sleve size (by hand) and adding enough water,
if necessary, to make the soil soft but not sticky. The pat of moist soil
should have a volume of about 1/2 cubic inch. The pat of soil is alter-
nately shaken horizontally in the open palm of one hand, which is gtruck
#
vigorously against the other hand several times, and then squeezed oetween
the fingers. A fine-grained soil that is nonplastic or exhibit8 wry low
plasticity will become livery and show free water on the surface while
being shaken. Squeezing w ill cause the. water to disappear fra the sur-
face and the sample to stiffen and finally crumble under increasing
finger pressure, like a brittle material. If the water content is just
right, ehaking the broken pieces will cause them to liquefy again and
flow together. A distinction may be made between rapid, elow, or no re-
action to the shaking test, depending on the speed with which the pat
changes its consistency and the water on the surface appears or dle-
appears. Rapid reaction to the sheking test is typical for nonplastic,
uniform fine eand, silty sand (SP, SM), and inorganic silte (ML)

particularly of the rock-flour type, also for diata~aceoua earth (M).
The reaction becanes somewhat more eluggieh with decreasing uniformity
of gradation (and increase in plasticity up to o certain deme). Even a
slight content of colloidal clay will Impart to the soil caw plasticity
and slow up materially the reaction to the ohaki~r, test. Soils which
react la this manner are sawwhat phstic inorganic aud organic silts
(ML, OL), very lean clayo (cL), and soma kaolin-type claye (ML, MB). Ex-
tremely slow or no reaction to the shaking test ie characteristic of all
typical clays (CL, CE) 8s wli as of highly plastic organic clays (a).
23. Plasticity characteristics. Exrmio.tion of the pWticity
characterietics of fine-grained soils or of the f ina fraction of coarse-
grained soils is ma& with a small moist tranrgle of the material. Parti-
cle~ larger than about the No. 40 sieve size are removed (by hand) and 8
specimen of soil about the uize of a 1/2-in. cube ie molded to the con-
sistency of putty. If the soil is too dry, water muat be added and if
it is sticky, the specimen should be spread out in a thin layer and
allowed to lose some moisture by evaporation. The sample is rolled by
hand on a smooth surface or between the palms into a thread about 1/8 in.
in diameter. The thread is then folded and rerolled repeatedly. During
this manipulaticn the moiature content is grad~ally reduced and the speci-
man stiffens, finally loses its plasticity, and crumbles when the plaetic
limit is reached. After the thread crumbles, the pieces should be lumped
to~ether and a slight kneading action continued until the lump crumbles.
The higher the poeitiun of a soil above the "A" line on the plasticity
chart, plate 2 (cL, CH), the stiffer are the thread6 as their water con-
15

soil is molded after rolling. Soils slightly above the "A" line (CL, 1
CH) form a mdium tow thread (eany to roll) a8 the phetic limit is i 1
I 1
approached but when the threads are formed into a lump and kneaded below i
the plastic limit, the soil crumbles readily. Soils below the "A" line
(ML, M?, OL, OH) form a weak thread and, with the exception of the OH
soils, cannot ba lumped togtther into a ooherent mass below the plastic
1 Plsstic soil8 containing organic material or much mica (well
below the "A" line) form mads that we very soft and rpongy near the
plastic limit. 'Ihs bin&r fraction of coarse-grained soilc msy be ex-
mined in tbe same auwr as ?be-grained soils. In general, the binder
fraction of coartle-pained eoile with eilty fines (OM, SM) vill exhibit
plasticity characteristice similar to the ML soila, and that of coarse-
pained soils vlth clamy fines (w, SC) w ill be similar to the CL eoile.
24. Dm rtmngth. The reelstance of a piece of dried soil to
etvohing by f-r preesure ie an indication of the chcrracter of the
colloidal traction of a soil. To initiate the test, pnrticler larger
than tne No. 40 sieve size are removed from the 8011 (by hand) and a
specimen ie moldad to the consietency of putty, adding water if neces-
sary. The moiet pat of soil is allowed to dry (in oven, sun, or air)
and is then crumbled between the fingers. Soils with slight dry strength
crrrmble readily with very little finger pressure. All nonplastic ML and
MEI soila have almost no dry etrtngth. Organic eilte and lean organic clays
of low plasticity (oL), as well as very fine sandy soils (sM), have
slight dry strength. Soils of medium dry etrength require considerable
finger pressure to pcru&r the sample. Most clays of the CL group and
eome OEI soil8 exhibit medium dry strength. This is also true of the fine
I
4
8
I
\

fraction of gravelly and sandy soils h.ving a clsy bider (W and SC).
Soil8 with high &y atrength can be broken but cannot be powdered by
fhger pressure. High dry strength is indicative of most CH clays, ae
well as sane organic clays of the 08 gruup havlns very hi& liquid llmit8
and located near the A-line. In sams instances hi@ dry rtrength in the
undisturbed etate may be furniehod by a cementing nvteriil ouch u cal-
cium carbonate or iron oxide.
25. Culor. In field soil surveys color 18 often helpful in dim-
tinguiehixq between varioue soil strata, and to an engineer with suffi-
cient preliminuy experience with the local eoils, color may also be
ueefil for identifying individual soile. The color of the moist soil
should be used in identific8tion u, soil color may change wkedly on
drying. To the experienced eye certain dark or drab eh.dte of gray or
brown, including almost black colors, are indicative of fine-grained
soile containing organic colloidal matter (OL, OH). In contraat, brighter
colors, including medium and light gray, olive green, brown, red, yellow,
and white, are generally associated with inorganic soile. Uee of the
Munsell soil color charts and plates, prepared for the U. S. Department
of Agriculture by the Munsell Color Company, Baltimore, Maryland, is
suggested in the event more precise soil color descriptions are desired
or to facilitate uniform naming of soil colors.
26. Odor. Organic 8011s of the OL and OH groups usually have a
dietinctive odor which, with experience, can be used as an aid in the
identification of such materiale. Thie odor is especially apparent h'om
fresh samples. It gradually dlminishea on exposure to air, but can be
revived by heating a vet 3ample.

Hi~hly orsrnic soil8
27. The field identification of highly organic soils (soup Pt) is
relatively easy inarrmuch as these soils are characterized by undecayed or
partially carbonized particles of leaves, sticks, grase, and other vege-
tablo matter which impart to the eoil a typical fibrous texture. The
color ranger generelly fran vrrious rhades of dull brown to black, A
dirtinct or&.nic odor is also characteristic of the soil, The water con-
tent ia urually very high. Another aid in identification of these soils
may be the location of the 8011 with respect to topography: low-lying,
8wampy areas uaUy contau hi@y orwic roils.
Laboratory IQntification
28, The identification of soils in the laboratory is accampliahed
by datermining the gradation and p.lastlcity characttristics of the mate-
rials. The gradation is determined by sieve analysis and a grain-size
curve is usually plotted as per cent finer (or passing) by might sgainrt
a 10~1-thmic scale of grain size in millimeters. Plate 1 is a typical
grain-aize chart. Plasticity charscteristice are evaluated by means of
the liquid and plastic limits tcete on the eoil fraction finer than the
No. b0 sieve, A suggested laboratory methoC of identification is pro-
sented schematically ia the chart shown as tabla 2 and is discussed in
the succeeding paragraphe. It ehould be recognized that although a def-
inite procedure for identification is outlined on the chart, the labora-
tory technician engaged in c1assif:cation may be able to uoe "short cuts"
in his work after he becanes thoroughly familiar with the criteria for
each soil poup.

Idnntification of mador soil uroups
29. Reference to the identification procedure chart, table 2, shows
that the first etep in the laboratory i&ntiflcatlon of a soil is to
determine whether it is coarse grained, fine grained, or highly organic.
This may be done by visual examinattion in most cases, using the procedures
outlined for field identification. In some borderline cases, a8 with
very fine eands or coar8e silts, it may be necessery to screen a repre-
sentative dry sample over a No. XIO eieve and deternine the percentage
paseing. Fifty per cent or less passing the No. 200 sieve idtntif lea
the soil as coarse grained, and marc than 50 per cent identifies the 8011
a6 fine grained. Tha percentage limit of 50 hss been selected arbitrarily
for convenience in identification as it is obvious that a numerical dif-
ference of 1 or 2 in this percentage will make no eignificant change in
the behavior of the eoil. After the major group in vhich the soil belongs
is established, the identification procedure is continued In accordftnce
with the proper headings in the chart.
Identification of subgroups,
coarse-pained soils
1
30. Gravels (G) or sands (s). A complete sieve analysis is run on I I
coarse-grained soils and the gradation curve is plotted on a grain-size
chart. For same soil8 containing a substantial amount of fines, it may
I
!
be desirable to supplement the sieve analysis with a hydrometer anal.ysis
I
!
I
in order to define the gradation curve below the No. 200 sieve size. Prelimlnary
identification is made by determining the percentage of material I
in the gravel (above No. 4 sieve) and sand (NO. 4 to No. 200 sieve) sizes. t
If there iu a greater percentage of gravel than sand the material I
is
!
I !
I

classed as gravel (0); if there ie a greater percentage of sand than
gravel the material is classed as sand (s). Once agair, the distinction
between three groups is purely arbitrary for convenience in foll.owing
the system. The next identification step is to determine the amount of
rraterial gaesing the No. 200 sieve. Since the subgroups are the same
for gravels and sands, they will be discussed jointly in the following
paragraphe,
31. O W ,
and 34 ,qroupe. Thene groups comprise nonplastic
8011s having lese than 5 per cent paesing the No, 200 sieve and in which
the fine fraction does not interfere with the soils1 free-draining prop-
ertiea. If the above criteria are met, an exsmination is made of the
shape of the grain-size curta. Materials that are well graded are clas-
sified as C)IJ or SW; poorly-graded materials are classified su OP or SP.
The grain-size distribution~l of well-graded materials gener~lly plot a6
smooth and regular concave curveo with no sizes lacking or no excess of
material in any size range (plate 3); the uniformity coefficient (60 per
cent grain diameter divided by the 10 per teat grain diameter) of well-
graded gravels 1.8 greater than 4, and of well-graded sands is greater
than 6, In addition, the gradation curves should meet the following
qualification in order to be claseed ae well graded.
D€o Dl0
between 1 and 3
where D30 = graln diameter at 30 per cent passing
D60 = grain diameter at 60 per cent passing
D10 - grain diamter at 10 per cent passir~g
The foregoing expression, termed 8 coefficient of curvature, inoures

that the grading curve will have a concave curvature within relatively
narrow limits for a given D60 and D1O combination, All grada'rione not
meeti~g the foreqoing criteria are claered ae poorly graded. Thus,
poorly-graded soils (OP, SP) are thoee having nearly etraight line gra-
dations (plate 4, fig. 1, curve 3), convex gradntions, marly vertical
(uniform) gradations (plate 4, fig, 1, curve l), and gradation curves
with "humpstL typical of skip-graded matarials (plate 4, fig. 1, curve 2).
32, OM, SM, QC and SC groups. The soils in these groups are corn-
posed of thoee materials having more than a 12* per ceut fraction passing
the No. 200 sieve; they may or may not exhibit plasticity. For identi-
fication, the liquid and plastic limits tests are required on the frac-
tion finer than the No. 40 sieve. The tests should ~e run on representa-
tive samples of moist material, and not on. air- or oven-dried soils.
This precaution is desirable as drying affects the limits values to same
extent as will be explained further in the discussion of fine-gxained
solls. Materials in which the liquid limit and plasticity index plot
belov the "A" line on the plasticity chart (plate 2) are classed as
Gb1 or SM (plate 5). Gravels and sands in which the liquid limit and
plasticity index plot above the "A" line on the plcrsticity chart are
classed as GC or SC (plate 6). It is considered that in the identifi-
cation of mater?.als in these groups the plasticity characteristics
,
overshadow the gradation characterietics; therefore, no distinction is ,
made between well- and poorly-graded materials. 1
* In the preceding paragraph soila of the GW, GP, SW, and SP groups were
defined as having less than a 5 per cent fraction passing the No. 200
sieve. Soils having between 5 and 12 per cent paesing the No. 200
sieve are classed as "borderline" and are discussed in paragraph 33.
I
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!
i
*I

33. Borderline soile. Coaroe-grained soils containing bettreen
5 and 12$ matcrial passiw the No. 200 sieve are clasoed as borderline ..
and carry n h l
symbol, e.g., OW-OM. Similarly, coarse-grained soils
having less thm 5% passing the No. 200 oieve, but which are not free
drainina, or vherein the fine fraction exhlbits plasticity, are also olaesed i
ao borderline and are given n dual symbol. Additional discussion of border- 1
line classification is prese2ted in parqpaphs 38-41. 1
Identification of sub-
poups, fine-grained soils
I
34. Use of plasticity chart. Once the identity of' a fine-grained 1
soil bas been established, further identification is accompliehed grin-
cipally by the Liquid and plastic limits teeto in conjunction with the
p3.asticity chart; (plate 2). The plasticity chart was developad by lk.
I
1 1
Caeagrande as the result of considerable experience with the behavior of
soils in many different regions. It is a plot of liquid limit versue plae-
ticity index on which is imposed a diagonal line celled the "A" line and a
vertical line at a liquid limit of 50. The "A" line is defined by the
equation PI = 0.73 (~20). The "A" line above a liquid limit of about \
I
29 represents an important empirical boundary between typical inorganic
cleys (CL and CII), which are generally located above the line, tad plwtic
soils contsining organic colloide (OL and OH) or inorganic silty eoile (ML
an6 Mi). The vertical line at liquid limit of 50 separatee silts and
clays of l2w liquid limit (L) From those of hi& liquid limit (H). In
the low part of the chart below a liquid limit of about 29 and in the
raDge of PI from 4 to 7 there ie conalderable overlapping of the proper-
tie8 of the clayey and silty ?oil typea. Hence, the ecparation between
I
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!
!
!

CL and OL or ML soil types in this region is accomplished by a cross-hatched
zone on the plasti?ity chart between 4 and 7 PI enrl above fhe "A" line.
CL eoils in this region are those having a PI above 7 while OL or ML soils
are those having a PX below 4. Soile plotting within the croes-hatched
zone should be claseed as bqrderline a8 diecussed later. The various eoil
wougs are shown in their respective positions on the plaeticity chart.
Experience hao shown that coatpessibility is approximately proportional to
liquid limit and that soils having the same liquid limit possess approxi-
mately equal compresoibility, assuming that other factors are essentially
the same. On comparing the physical characteristics of soils having the
same liquid limit, one finds that with increasing plasticity index, the
cohesive characteristics increase and the permeability dec~.eases. From
plots of the results of limits tests on a number of samples from the
earne fine-grained deposit, it is found that for most soils these points
lie on a straight line or in a narrow band approximately parallel to
the "A" line. With thio background information in mind, the identifica-
tion of the various groups of fine-grained soils is diocussed in the
follo~iog paragraphs.
35. ML, CL, and OL groups. A soil having o liquid limit of less
than 50 falls into the low liquid limit (I,) group. A plot of the liquid
limit and plaoticity index on thc plasticity chart will show whether it
falls above or below the "A" line and croes-hatched zone. Soils plotting
above the "A" line and csoos-hatched zone are classed aa CL and are usually
typical inorganic cltiys (plate 8, fig. 1). Soils plotting below the "A''
line or cross-hatched zone are inorganic silts or very fine oandy oilto,
ML (plate 7, flg. l), or organic silts or organic oilt-clays of low

plasticity, OL (plate 9, fie. 1). Since two groupe fall below the "A" line
or cross-hatched zone, further identification is necessary. The dietin-
guishing factor between the MI, and OL moupe ie the abeence or presence
of organlc matter. This is usually identified by color and o&r as
explained in the preceding paragraphs under field iflentification. How-
ever, in doubtful cases a comparison may be made between the liquid and
plastic limits of a mist sample and one that ha8 been oven-dried, An
organic soil will shoxr G radical Uop in plasticity after oven-drying
or air-drying. An inorganic soil will generally show a change in the
limits value6 of only 1 or 2% which may be either an increase or a decrease.
For the foregoing reasons the classification should be based on the plot
of limits values determined before drying. Soils containing organic matter
generally have lower specific mavities md may have decidedly higher water
contents than inorganic soils; therefore, these properties may be of assiet-
ance in identifying organic soils. In special cases, the determination of
organic content may be made by chemical methods, but the procedures just
described are usually sufficient.
36. MH, CH, and OH groups. Soils with a liquid limit @eater than
50 are classed in moup H. To identify such soils, the liquid limit
md plasticity index values are plotted on the plasticity chart. If the
points fall above the "A" line, the soil classifie~ as CH; if it falls
below the "A" line, a determination is made as to whether or not organic
material is present, ae described in the preceding paragraph. Inor~anic
materials are classed as MI and organic materiala are classed as OH.
Identification of highly organic 6011s
37. LAttle more c~ln be said as to the laboratory identification of

highly organic soils (Pt) than has been stated pp.wiously under field
identification. These soils are usually identified readily on the basis
of color, texture, and odor. Moisture determinations usually show a
natural water content of sweral hundred per cent, which is far in ex-
ceso of that found for wet soils. Bpecific gravities of the solids in
these roils may be quite low. Some peaty soils can be remolded and
tested for liquid and plastic limits. Such mterials usually have a
liquid limit of sweral hundred per cent and fall well below the "A"
I line on the plasticity chart.
i Borderline classifictutions
38. It is inevitable in the use of the clessificttion system that
eoils will be encountered that fall close to the boundaries established
between tiic various groups. In addition, boundary zonee for the amount
of material passing the No. 200 siwe and for the lower part of the
t
I t
plasticity chart have been incorporated ao a part of the system, as
discussed subsequently. The accepted rule in classifying borderline
I
soils is to use a double symbol; for example, GkI-GM. It is possible, I
in rare instances, for a soil to fall into more than one bordcrline zone
I
and, if appropriate symbols were used for each possible classification,
\ I
I
1
the result would be a multiple designation consisting of three or more
symbols. This approach is unnecessarily complicated and it is considered
!
I
I
best to use only a double symbol in these caaes, selecting the two that
I
are bellwed most representative of the probable behavior of the soil.
In cases of doubt the symbols representing the poorer of the possible
I
1
groupings should be used. I
39. Coarse-grained eoils. It will be recalled that in previous

I--
I
I
I
I
26
discussions (gsragraph 31) the coarse-gralned soils were classified in
the GI!, OP, BW, and 8P groups if they contained less than 5% of mterial
par9ing the No. 260 sieve. Similarly, soils were classified jn the OM,
UC, SM, and SC gruups if thy had more than 12s passing the No, 200 miwe I
(paragraph 32). Th range between 5 and 125 passing the No. 200 seive is
designated a8 borderline, and soils fallin8 within it are assimed a double
symbol depeaCHng on both the gradation characteristics of the coarse
I
fraction and the plasticity characteristics of the minus No. 40 sieve
fraction. For example, a well-graded sandy soil with "5 passing the W.
200 sieve and with LL = 28 and PI = 9 would be designated ns SW-SC.
I
1 I
hther type of borderline classification occurs for those soils containing
appreciable amounts of fines, groups DM, GC, SM, and SC, and whose
Atterberg limits value8 plot in the lower portion of the plesticity chart.
The method of classifying thelre soils ie the aame as for fine-mainad
soils plotting in the same region, a8 peaented in the following pagraph.
40. Fine-grained soils. Mention has been made of a zone on the
plasticity chart (plate 2) below a liquid limit of about 29 and raaging
i
j
1
between plasticity index values of 4 en8 7. Several soil types exhibitin6 I
low plaeticity plot in thie general region on the plasticity chart and no
definite boundary between silty and clayey soils exists, Thus, if a fine-
grained soil, groups CL and ML, or the anus No. 40 siwe fraction of a
coarse-pained soil, group8 CM, GC, SM, and SC, plots within the croae-
hatched zone on the plaoticity chart, a double symbol (ML-CL, etc.) is used.
41. "811ty" and "clayey." It vill be .loted on the classification
sheet, table 1, that the adjectives "siity" and "clayey" mey be used as
part of the descriptive name for silt or clay soils. Since the
I
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!
i
I 1
i
1
I

deflnitionr of thee term are naw ramwht different from thore used by
many roils engineerr, it is considered advlrable to discur their connota-
tion as used in this eyeten. In the unified soil claerification the tsnns
"rilt" .nd "clay' are used to deecrlbe those rroilr with Atterbarg limite
plotting respectively below and above the "A" line and cross-hatch46 %one I
on the plasticity chart. Ar a losical extenrion of tbis concept, the torme
Itrilty" and "clwey" may be wed M adJectiver in the roil namsr when the
llmitr values plot close to the "A" line. Fbr emle, a clay ooil wlth
LL = 40 sn8 PI = l6 may be celled a rilty clay. In general, the adjective
"silty" is not applied to clw roflr having a liquid limit in excerr of
42. It WQ' be necessary, in some caees, to expend the unified clcrs-
rification oystem by subdivision of existing group in order to claseify
roile for a particular use. The indiscriminnte we of subdivirioae ie
discouraged and careful study ebauld be given any soil mot@ before much
s rtep is adopted. In all cues eubdivisions should be designated pref-
erably by a ruffix to an exirting moup rymbol. The ruffix ebould be
relected cuefully la that there will be no conftmion with exlrtirrg let-
term that drew have meatringr in the clssrification system. In each
cue whare m exioting -up ir eubdivided, the buir and criteria for
the rubdivieion dmuld be explained in order that aqyona unfamiliar with
it undarrtmd the rubdlvieion properly.

De8criptive Soil Classif ication
43. At many stages in the soils investigation of a prodect --
froan the preliminary boring log to the final report -- the engineer
finds it convenient to give the soils he is working with a "name" rather
than an "Impersonal" classification symbol such as OC, This results
primarily from the fact that he is accustomed to talking in terms of
gravels, sands, silts, and clays, and finds it only logical to use these
same names in presenting the data, The soil name6 have been associated
with certain grain sizes in the textural classification as sham on the
grain-size chart, plate 1, Such a divieion is generally feasible for
the coarse-grained soils; however, the use of such terms as silt and
clay may be entirely misleading on a textural basis, For this reason
the terns "silt" and "clay" have been defined on a plasticity basis as
discussed previously. Within a given region of the country, use of a
name classification based on texture is often feasible since the general
behavior of similar soils 16 consistent pvcr the area. However, in
another area the same classification may be entirely inadequate, The
descriptive classification, if used intelligently, has a rightful place
in soil mechanics, but its use should be carefully evaluated by all
concerned.
Description from classification sheet
44. Column 4 of the classification sheet, table 1, lists typical
name8 given the soil types usually found wlthin the various claseification
groups. By following either the field or laboratory investigation pro-
cedure and determining the proper classific :tion group in which the soil

i
..I
belongs, ',t ie urually an easy matter to selec t, an appropriate namc from
the claseificatLon eheet, Scw soils may be readily identified and prop-
erly named by only viscal inepection, A vord of caution is considered
appropriate on the use of the claseitication ajtsttnn f o certain ~ soils
such a8 marle, caliches, coral, shale, etc., where the grain size can
vary widely depending on the amount of mechanical breakdown of soil par-
ticles. For these soils the group eymbol and textural name have little
significance and the loca!ly used name m y be important.
Other daecriptive terms
45, Rccords of field explorations in the form of boring logs can I
be of great benefit to the engineex* if they include adequate information, I
In addition to the group symbol and the name of the soil, the general
I
characterletice of the soils as to plasticity, strength, moisture, etc., I 1
I
provide information essential to s proper analysis of a particular prob-
I
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t
lam. Locally accepted 8011 names should also be used to clarify the
data to local bidders, and to protect the Government against later legal
i claims. For coarse-grained soils, the size of particles, mineralogical
i
I ccmposition, shape of grainc, and character of the binder are relevant
I
!
features, For fine-pained soils, strength, moisture, and plasticity
! characteristics are important. \hen describing undisturbed soils such
characterietics ss stratification, structure, coneiatency in the undis-
turbed and remolded states, cementaticn, drainage, etc., are pertinent
to the descriptive classification, Pertinent items to be used in de-
scribing soils are shown in column 6 of table 1, In order to achieve
uniformity in estbating consistency of aolls, it is recommended that
the Terzaghi clasaificetion based on unconfined cmpressive strength be
!
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!

wed as a tentative stmdard, This clarrrificwtion i8 given below:
Unconfined Comprersive Btrength
~ons/~q Ft Conrietenc y
< 0.25 Very soft
0.25-0.50 sort
1,OO-2.00 Stiff
2.00-4,OO Very stiff
Several examples of descriptive claseifications are sham below:
aA Uniform, fine, cleaa sand with rounded grains (sP) .
b_. Well-graded gravelly silty sand; angular chert gravel,
1/2-in. maximum size; silty bin&r with low plasticity,
well-compacted a d moist (SM) ,
- c. Light brown, flne, eandy silt; very low plasticity; saturated
and soft in the undisturbed atate (ML) ,
- d. Dark gray! fat clay; stiff in the undisturbed etate; soft
and sticky when remolded (a).

. . .
. : : . !
.. !:..I,.. I.. ..

I
I
(pt)
likour texture, color, odor,
wry hi& moirture content.
I
particlea of vegetable matter
(rtickr, loaver, eta.) I
paor lo. 200 rieve
Bordrrline, to have
doubla rymbol appro-
plaoticity character-
irtica, 0.6. 6Y-M
Note: Bieve sizes are U. 8. Btandsrd.
I COARSE 0RAIm;D I'
1
5M or lerr pass No. 200 aieve
I
Run rieve wlytia
+--I
If finer interfere vith free draining propertier ure double rymbol ouch as GU-OM, etc.
021260-B
r$??
I Lars than 5% pars
No. PO0 sieve*
graded graded
Examine grain
eite curve

I
Table 2
AUXILIARY LABORATORY IDEIJTIlICATION RIOCEDURE
1
Betweon 5$ and 12% More than la pad8
pare No. 200 eleve No. 200 sieve
.- - --- -- .---.--- -A
double symbol appro- Run LL end PL on Color, odcr, porribly
priate to grading and minl~a No. 4C eieve LL and PL on over1 dry
-

A .
. J
PIICE mm
nore than 501 par8 lo. 200 rieve
I
Run Lt and PL on minur lo. CO sieve
material
I
L
Liquid limit :ear thnn
H
Liquid limit greater th.a
50 50
I I I
I
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I
Belov "A" line or
natched zone on
Limite plot In
hatched zone on
Above "A" line and
hatched zone on
Belov "An line
on plasticity
Above "An line
on plasticity
plasticity chart
I
plaetlcity chnrt plaaticity chart chart
I ,
chart
C2:or, odcr, possibly Color, odor, porribly
LL and PL an oven dry LL and PL on oven dry
sc! l soil
I I
I I + I
C
Organic Inorganic Inorenic Or(pnic
I . .
- l I
I -
OL ML ML-CL C L 101 OR CB
uu u
J

PLATE I

PLATE 2

MII61-A
I
.Ur*Un-
U 1 - - I 1
U.U
CllM 11 ?it run uav*l) nonphrtlcl Wll-Wd~ -11 WrcenU.) of rim*.
CLIIIVC P: hrdy UaWlr nonplarllcr no tlwa. Cvrn la about tba rt..pml ma Ck.1 rill mt UI crlUrw f a
w em?.
u a a1kn~m m nu
1 (..D - I m
W *,a I -ut.II
ClAVl 1: bdlu to fIw &: nonplretlel -11-uhd.
UrIa tor W UAID.
W P:. Oranlly mandl nonplaailcl -11-pa&(.
Cwn I# about tha atnmat m *.I dl1 mt Cb. crl-
:, ,-, I U.U 1
TYPICAL EXAMPLES
GW AND SW SOILS
PLATE

PLATE 4
I - t
ma La1 a n ~UlttM - - I, ,'I , I .I m U
CMVL ;: Uolton .-t wa qar.11 nonp:retlr. Vmry unllon paktlon.
d.Btdi k. Ctrrml-land mlmtwe; nonplactlr. Orrvel La .hat all of am all* (31h. to I.ln.), no fln ulral
prement. borly y.b.d.
mvr 1: mnq wave11 n~nplat'.~~. AII ata+n UI prerent, but UW~IM aorc nat WL rurrrtw rrlwrloa for w.
c'JRVt 1: Onllan flne land: nonF:amtlc.
clmvr 2; k~t;~ 0.0.d 'rave11y t.nd a~xtu.~ o~np:actlc. ~ppromluuly 7 p r cmt flna YLca Ulm a Wrrllm
8~11, ljmhLl 8Y.M.
fb-a 1: roua to rdlw sanl; n~np!rmtlc. Appmchl~ unlron uad.llon; dnl not ret cunrtura crl~rloo
for 6Y.
3P GROUP
CIC. 1
TYPICAL EXAMPLES
GP AND SP SOlLS

w-.'. ..r--. '"r- .---,--- . . - r - . v r. r a . :..
.
.C .
............... . . .
--- - . -. ....
.... -
.U UI m -unr
C Y t r T m - 1 m I u em 1
LmW 8 : , ... : .., .. .U-'
. '
-. L:* LL d i
-
- '
. . . . .
I
I
I
1
j
,
1
!
'
:I
I .
I

LXMW 11 CAq-gaml (chrOl LL-UJ, n-19. hlr4 la preen- of viami~t tlut.
EUVl PI ktw.1 .Latun OK wa*rl ud clyl Ltbf, ?l-PO. Vary prly p.d.dj rlw.olt no sea4 01~1 pr*.ant.
GC GllOUC
'LATE 6 30
TYPICAL EXAMPLES
GC AND SC SOILS
I

Y I .1- W". mu
.y m I -**a
Y I I - 1 - 1 1 - 1 I I v m u I
-
CWW 1: Uew*oua W alltl U-39, Kd.
oun o: MI a11t1 ~i n.m.
n*n 3, Clq., .lltl u.6 n-H.
QUL! mou I i h.r wawuw u. II.~ *II - ~16.4 ummt 11 w t t a ~ t v ~
Mn GIIOUC
116.1

PLATE 8
CL CROUP
IIC.1
TYPICAL EXAMPLES
CL AND CH Sol LS

I
.LU I. ..-MI
u k - T a !-+ .tau I
CUYI I: Or(mle ely (tld.1 tIataJ~ U-95, n-39.
CUM PI 1-11 clay w~th armle mttora LLS n-or.
Cum 1: Orwlc allt; U-lo, n-13 (mtkl ntr cknrrot11 I;-51, n.19 (n.n drl.4).

APPENDIX A
CHARACTERISTICS OF SOIL GROUPS PERTAINING TO
EMBANKMENTS AND FOUNDATIONS
Sponaod by
Office, Chid of Enginwn
U. S. Army
Conduthd by
U. S. Army Engineer Wahmaya Experiment Station
CORPS OF ENGINEERS
Vickrburg, Mirrisrippi

Content 8
Introduction ........................... Al
Feature8 Shown on Soile Claeeification Sheet ........... A2
Graphical Presentation of Soils Data ............... All
Table A1
EE

UlVPIED SOIL CLASSIFIC4rPION SYSTEM
CHARACTERISTICS OF SOIL GROUPS F'ERTAINXNG TO
EMUMWHTS AND FOUIVDATIOYS
Introduction
1. The mador propertlee of a 8011 proposed for use in an embank- I
!
ment or foundation that are of concern to the deeign or construction
engineer are ite etrength, permeability, and consolid~tion and compaction
i characteristics. Other features may be inveetigated for a specific problem,
but in general some or all of the propertiee mentionod above are of
I
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I
1
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i
I I
primary importance in an earth embankment or foundation project of any
magnitude. It 18 common practice to evaluate the properties of the eoila
in question by means of laboratory or field tests and to use the result8
of such testa as a baeie for heaigc and conetruction. The factore that
influence strength, consolidation, and other characteristice are numerous
and sone of them are not completely understood; consequently, it is im-
practical to evaluate these features by means of a general soils clae-
sification. However, the eoil groups in a given claseification do have
1
I reasonably similar bahavior characteristics, and while such information
i
is not sufficient for design purposes, it will give the engineer a? indi-
I
I
cation of the behavior of 8 soil when used as a component in construction.
This ie especially true in the preliminary examination for a project when
neither time nor money for a detailed soils testing proarm is available,
2. It should be borne in mind by engineere using the clasoification
n-I
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that only generalized characteristice of the eoil groups are included
therein, and they ehould be ueed primarily as a guide and not as the com-
plete answer to a problem. For example, it ie poeeible to design and
construct an earth embankment of almoet any type of soil and upon prac-
tically any foundation; thin is in accordance with the worth-while prih-
ciple of utilizing the materials available for conetruction, However,
when a choice of materials is possible, certain of the available soils
may be better euited to the job than others, It 16 on this basis that
the behavior characteristics of soils are presented in the following pars-
graphs and on the claesification eheet. The L U to ~ which 8 structure ie
to be put io of'ten the principal deciding factos in the selection of soil
types as well as the type of protective mbasures that will be utilized.
Since each structure is a egecial problem within itaelf, it 18 impossible
to cover all poeeible conaideratione in the brief deecription of perti-
nent 8011 characteristic8 contained in thie appendix.
Features Shown on Soils Clseeification Sheet
3. General characteristice of the evil groups pertinent to em-
'bankucnts and foundations are preeented in table Al. Columne 1 through
5 of the table show major eoil divi9ione, group symbols, end hatching
and color symbols; ntlnes of eoil types are given in column 6. The basic
features are the same as those presented in the soils claseificafion
nanuel. Columns 7 through 12 show the fcllowlng: column 7, euitabillty
of the materials for ..me in embankments (strength and permeability char-
acterietice); column 8, the minimum or range of permeability values to
be expected for the soil groups; column8 9 and 10, general conpaction
E
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characteristice; column 11, the euitability of the soil8 for foundation8
(strength and consolidation); and column 12, the requirements for seep-
age control, eopecially when the soils are encountered in the fouaQtion
for eartll embanknrents (permeability). Brief discussions of these fea-
tures are presented in the following parsgraphe.
Suitability of 8011s for embankmants
k, Three ma,jor factors that influence the suitability of boils
for u6e in embankments are permeability, strength, and ease of compac-
tion. The gravelly and sandy soils with little or no fines, groups GW,
GP, SW, and SP, are stable, pervious, and attain good compaction with
crawler-type tractors and rubber-tired rollers. The poorly-graded mate-
rials may not be quite as desirable as those which are well graded, but
a11 of the merterials are suitable for use in the pervious sections of
earth embankments. Poorly-graded sands (SP) may be more difficult to
utilize and, in general, should have flatter embankment slopes than the
SW soils. The gravels end sands with fines, groups GK, GC, SM, and SC,
hove variable characteristics depending on the nature of the fine frac-
tion and the gradation of the entire sample. These materials are often
sufficiently impervious and stab12 to be used for imperviobs sections of
embankments. The soils in these groups should be carefully examined to
insure that they are properly zoned with relation to other materials in
an embankment. Cf the fine-grained soils, the CL group is best adapted
for embanbent construction; the soils are impervious, fairly stable,
and give fair to good compaction with a sheepefoot roller or rubber-
tired roller. The MK 8011s, while not desirable for rolled-fill construc-

the ML group my cr my not have good compaction characteristice, and in
general must be closely controlled in the field to secure the dasired
strength. CH soils have fair stability when used on flat slopes but
have detrimntal shrinkag? characteristics which my r.ecessitate blan-
keting them or incorporating them in thin interior cores of embankmente.
Soils containing organic matter, groups OL, OH, and Pt, are not conmnonly
used for embankment construction because of the detrimentcl effects of
the organic matter present. Such naterials may often be utilized to ad-
vantzge in blankets and stability berms where strength is not of impor-
tance.
Penceability and seepage control
5.
Since the permeability (column 8) sna requirements for seepage
control (cclumn 12) are essentially functions of the sane property of a
soil, they will be discussed Jointly. The subject of seeoage in rela-
tion to embadaents and foundations may be roughly divided into three
categories : (1) seepage through embankments; (2) seepage through f ounda-
tions; and (3) control of uplift pressures. These are discussed in re-
lation to the soil groups in the following paragraphs.
5. Seepa~e through embankments, . In the control of seepage through
embankments, it is the relative permeability of adjacent materials rathcr
than the actual permeability of ~uch soils that governs their use in a
given location. An earth embankment 1s not watertight and the allowable
quantity of seepage through it is largely governed by the use to which
the rtructure is put; for exa~tple, in a flood-controi project consider-
able seepage may be allowed and the structure \-ill still fulfill the stor-
age requirements, whereas for on irrigation project much less seepage is

allowable because pool levels must be maintained. The more im$ervioue
uoils (OM, GC, SM, SC, CL, ME, and CH) may be used in core eectiontj or in
tomogenev~s embankments to retard the flow of water. Where it is impor-
tant that seepage not emerge on the downstream elope or the possibility
of drawdm exiets on upstream slopos, nore pervious materials are usual- I
ly placed on the outer slopes. The coarse-grained, free-draining 8011s
(OW, OP, SW, SP) are beat suited for this purpose. Where a variety of
materials is available they are usually graded from least pervlous to-
more pervious from the center of the embankment outward. Care ehould be
used in the arrangement of materials in the emban,hent to prevent piping
within the section. The foregoing staten;ents do not preclude the uee 02
other arrangements of materirle in embankmente. Dam have been con-
structed successfully entirely of sand (SW, SP, SM) or of silt (MY,) with
the section mde large enough to reduce seepage to an allowable value
I
without the use of an imperv~ous core. Coarae-grained soils are often i
used in drains arid toe section8 to collect eeepaee water in downstream
sections of embankments. The soils used will depend largely upon the
material that they drain; in general, free-draining sands (SW, SP) or
gravels (GW, W) are preferred, but a silty sand (SM) may effectively
drain a clay (CL, CH) and be entirely satisfactory.
7. Seepage through foundations. As in the cmse of embankmen

lo desired, then the more pervious roils are the 80111 in which aecersary
measurns muet be taken. Free-draining gravels (OW, UP) are capable of
carrying considarable quantities of water, and some moms of positive
control such an a cutoff trench may be necessary. Clem ran& (SW, SP)
may be controlled by a cutoff or by an upstream iqpervloua blanket.
Vhile a drainage trench at the downstream toe or a line of relief wells
will not reduce the amount of seepage, either will serve to control seep-
age and route the flow into collector systems where it can be led away
hamleesly. Slightly ltse pervious materiel, such as silty gravel8 (OM),
silty sands (sM), or silta (ML), may require a minor amount of seepage
control such as that afforded by a toe trench, or if ,hey are sufficient-
ly impervious no control may be necessary, The relatively impervious
soils (GC, SC, CL, OL, MH, CH, ~nd OH) usually pees such 8 small volume
of water that seepage control measures are not necessary.
8 Control of uplift pressures. The problem of control of uplift
pressures is directly associated with pervious foundation soils. tlplift
pressures may be reduced by lengthening thc pdth of seepage (by a cutoff
or upstream blanket) or by measure8 for pressure relief in the form of
wells, drainage trenches, drainage blankets, or pervious downstreem
shells. Free-draining gravels (CW, GP) may be treated by any of the
aforementioned procedures; however, to obtain the desired pressure relief,
the use of a positive cutoff may be preferred, as blanket, well, or trench
installations would probably have to be too exteneive for economical ac-
complishment of the desjred results. Free-draining sands (SW, SP) are
generally less permeaLia than the gravel6 end, coneequently, the volume
of water that must be controlled for pressure relief is usSlally less.

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Therefore a poritive cutoff may not be required and an upstream blanket,
welle, or a toe trench soy be entirely effective, In some ceses a combination
of blanket end trench or wells my be deeirable. Silty soils --
silty gravels (OM), silty ran& (a), and eilta (ML) -- usually do not
require extensive treatment; a toe drabage trench or well system may be
sufficient to reduce uplift pressures. The more impervious eilty mate-
riale may not be permeable enough to permit dangerous uplift preesures
to develop and in ouch cases no treatment is indicated. In general, the
more impervious soils (OC, SC, CL, OL, MB, CH, and OH) require no treat- I
ment for control of uplift prerswes. However, they do aesums impor- i
tance when they occw as a relatively thin top stratum over more pervioue
materials. In such cases uplift pressures in the lower layers acting on
the baee of the impervious top stratum can cause heaving and formation of
boils; treatment of the lower layer by some of the methods mentioned
above is usually indicated in these cases. It is emphaeized that dontrol
of uplift pressures should not be applied indi~criminntely duet be- 1
cause certain types of soils are encountered. Rather, thc use of control
I
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I
measures should be based upon a careful evaluation of conditions that do
I i
or can exist, and an econominal solution reached that will accomplish !
the desired results.
Compaction characteristice
9.
In column 9 of the table are shown the general compaction char-
acteristics of the various soil groups. The evaluations given and the
equipment listed are based on average field conditione where proper
moisture control and thickness of lift are attained and a reasonable nwn-
be- of passes of the compaction equipment is required to secure the
I

desired denrity. For lift constructSon of embankments, the eheeprfoot
roller and rubber-tired roller are colll~ronly used piece8 of equipment.
Soms crdvantagee may be claimsd for the eheepsfoot roller in that it
leaves a rough rurface that afford6 better bond between liitr, and it
heado the soil thus affording better moisture dirtribstion. Rubber-
tired equipnunt referred to in the table is considered to be heavily
loaded compactore or earth-moving equipment with a minimu wheel load of
15,000 lb . If ordinary wobble-wheel rollere are used for conpaction,
i the thickness of compacted lift is ueually reduced to about 2 in. Oranuhr
eoile vlth little or no finer generally show good coxr,paction char-
1
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P
1
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L 80ils in mo~t
acterieti~a, with the well-graded materials, GW and SW, usually f+aniah-
ing better reeuSte than the poorly-graded soils, OP and SP. The eandy
cases are best compacted by crawler-type tractors; on the
gravelly materials rubber-tired equipment and sometimes steel-wheel rollers
are also effective. Coarse-grained soils with fines of low plasticity,
groups GM and SM, ehow good compaction characteristics with either sheeps-
foot rollers or rubber-tired equipment; hcwever, the range of moisture
contents for effective compaction may be very narrow, and close moieture
control is desirable. This is also generally true of the silty soils in
the ML group. Soils of the ML group may be compacted with rubber-tired !
equipment or with sheepsfoot rollers. Gravels and sands with plaetic
fines, groups GC and SC, ehow fair compaction characterietics, although
this quality may vary somewhat with the character and amount of fines;
rubber-tired or sheepsfoot rollers m y be used. Sheepsfoot rollers are
generally used for compacting fine-grained soils. The compaction char-
bcterietice of such materials are variable -- lean clays and sandy clays
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(CL) being the best, fat clays and lean organic cl~ys or silts (OL and CH)
fair to poor, and organic or micaceous soils (MH and OH) usually poor.
For most construction project8 of any mcgnitudc it i, highly deeirable
to investl&ata the compaction characteristics of the soil by mans of a
i field test section. In column 10 of table A1 are shown ranges of unit
1 dry weight of the soil groups for the standard AASHO (proctor) compactive
1 effort. It is emphasized that theae values tre for guidance only and de-
1
!
I
sign or conetruction control should he based on laboratory test results.
Suitability of soils for foundations
10. Suitability of soil8 for foundationc of embankments or struc-
tures is pritdarlly dependent on the strength and coneolidation character-
istics of the subsoils. Here again the type of structure and its use
will largely govern the adaptability of a soil cs a satisfactory founda-
tion. For embankments, large settlercents may be allowed and compenasted
for by overbuilding; whereas the allowable settlerent of structures such
as control towers, etc., may be small in order to prevent overstressing
the concrete or steel of which they are built, or because of the neces-
sity for adhering t~ established grades. Therefore a soil m y be entire-
ly satisfactory for one type of construction but may require special
treatment for other tjpec. Strength and settlenent characteristics of
mils are dependent upon a number of variables, such as structure, in-
place density, ~oisture content, cycles of loading in their geologic his-
tory, etc., which are not readily evaluated by a classiflcati~n systen
such as used here. For these reascns only very general statements can be
made as to the suitability cf the various soil types as foundations; this
is especially trud for fine-grained soils. In generel, the gravels and

gravelly 8011s (GW, GP, OM, OC) have good bearing capacity and undergo
little consolidation under load, Well-graded sande (SW) usually have 8
good bearing value. Poorly-graded eands and silty sands (SP, SM) may
exhlblt variable bearing capacity depending on their density; thi~ 1st
true to some extent for all the coarse-gralned eoils but is especially
critical for uniformly graded soils of the SP and SM groups. Such eoils
when saturated my become "quick" and present an additional construction
problem. Soils of the ML group may be eubJect to liquefaction and may
have poor bearing capacity, particularly where heavy structure loads are
involved. Of the fine-grained eoils, the CL group is probably the best
from e foundatiou standpoint, but in some cases the soils may be soft
and wet md exhibit poor bearing capacity and fairly large settlements
under load. Soils of the ME groups and normally-consolidated CH eoils
my ehow poor bearing capacity and large settlements. Organic soils, OL
and OH, have poor bearing capacity and usually exhibit large settlement
under load. For most of the fine-grained soils discussed above, the type
of structure foundation selected is governed by such factors as the bear-
ing capacity of the soil and the magnitude of the load. It ie possible
that simple epread footings might be adequate to carry the load without 1
I
exceeeive settlement in many cases. If the soils are poor and structure I
loads are relatively heavy, then alterne te ce thods are indicated. Pile
foundatioas may be necessary in some cases and in ~pecial instances, par-
ticularly in the caee of eome CH and OH eoila, it may be desirable and
economically feasible to remove such soils from the foundation. Highly
organic soile, Pt, generally are very poor foundatioa materials. These !
may be capable of carrying very light loads but in general are unsuited
I
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for moat conetruction purposes. If highiy organic soile occur in the
foundation, they may be removed if limited in extent, they may be die-
placed by dumping firmer soile on top, or piling may be driven through
them to a stronger layer; proper treatment will depend upon the structure !
.
i~volved
Graphical Presentation of Soile Data
11. It is cuetornary to present the resulte of 8011s explorations
on drawing6 or plans as schematic repreeentatione of the borings or test
pits with the oils encountered ehown by various spbole, Comonly use&
hatching symbols are small irregular round symbols for gravel, dote for
sand, vertical linee for silts, and diagonal lines for clays. Combinations
of theee symbols represent various combinations of mcrteriale found
in the explorationd, This system nas been adapted to the varioue eoil
groups in the unified soil claseification eyeten and the appropriate eym-
I
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'1
;
bole are ehown in column 4 of table Al. Ae an alternative to the hatch- I !
lng symbols, they may be cmitted and the appropriate group letter spbol
(CL, etc.) written in the boring log. In addition to the symbols on logs
of boringe, the effective size, D10 (grain size in rnm correeponding to 1
10 per cent finer by weight), of coarse-grained soils and the natural
water content of fine-grained soils should be shown by the side of the
! ..
log. Other descriptive abbreviations may be used as deemed appropriate. 1
In certain special instances the uee of color to delineate eoil types on
maps and drawings is desirable. A suggested color scheme to show the
major soil gr3ups is dascrlbed in column 5 of table Al.
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I Not used t3r con8tructlbn I C'l
lot..: 1. Vnluem in colwm 7 md 11 u e for yidance only. bslgn shou:d be baaed on test reoultm.
2. In colw 9, the equiprnt listed will uou&lly produce tho dealred denmitiem vith rn reasonable numbrr of p.rmem vhaa molrture conditlona .Y
3. ColumlO, unit dry rclghtm ue for coapactod #oil st optimum moisture content for Standard AA3RO (Stnrdud Roctor) cmpactive effort.

-
YlY atable. Dlwioua
ly *table, not putlcu-
E Ited to rhllr. but w
L a con
-
k > 10'~ 0406, tractor, rubber-tired, 125-135 0004 bruin4 value Forltive cutoff
@-el-uheeled roller
k > lom2 Ooad. tractor. rubber-tired. 115.125 -
Oood beuio. vrluo Foritiw cutoff
.t..i-vhrled'roiler
k 10.) ~ood, vith cloae control,
s
120-139 Oood beuim value Tea trench to noam
to lo4 rubbor-tired. eboe~rtoot
roller
II - lo4 (mi., rubber-ti~ed, ah~eprf~~tl 115-130 I 0004 WYL~L value INOW
to 10.8 roller I
le, prvioue aactionu, t > lo-3 ~aod, tractor l10-1j0 OM beuinL value Upatreu blanket md
CW dniM(. Or ~ e l h
ply aublr, uy bo ueed k, 10'3 0004, tractor 100-120 Oood to poor b@uin( Uprtreu blanket md
1 aectlon vltk Zht rlopoa value'depndlng on too &aim#e or wlla
dmnalty
not plvtieululy k - 10'3 0004, vith cloee control, 110-125 Oood to poor bmuint Upmtreu blmket md
rhellr, but uy b. to rubber-tired, rhmprfoot alum depndlng on toe &aimgo or wllm
imprviour corer or roller tienmity
table, ume for inperviour k - los6 Fair, mherprfoot roller, 105-125 Oood to poor beulna Nona
flood control to rubter tired value
very poor, auacepti- TOO trench to none
blr to liquef~tlon
impervlc urn corer and ~ood to poor beulna NOW
blc f ~ embankants r
hlr to poor beulna, None
m y have rrcermlve
illty, core of hydraulic
not demlrsble in rolled
E tmction
iliry with flat mloper,
E 8. blanket@ and dike
blm for embsnbntn ?
I I
k - la-' Poor to very poor, sheeysf>o: 73-05
to 10-6 roller I
Poor bcarlng
I . lnir to poor, mnepmcmt I 75-105 to 10-8 rolior
I 1
Qlr to poor beulna None
I I I I I
o very poor, mhe*pnfoat Very poor beulna
lot urrd for conmtruction I Cmpc tlon not prac tical I Remove frm :oundntlonm I
number of paleer vr.en noimture conditlonr md thicknemm of lift are properly controllad.
d MRO (8t.ndud Roctor) ccopactive effort.
I

TECHNICAL MEMORANDUM NO. 3-357
APPENDIX B
CHARACTERISTICS OF SOIL GROUPS PERTAINING TO
ROADS AND AIRFIELDS
Sponrond bv
Office, Chief of Engineers
U. S. Army
U. S. Army Engineer Waternays Experiment Stakion
CORPS OF ENGINEERS
Vickaburg, Miariarippi

Contento
..........
..................
.................
Introduction.......................... B1
Features Shown on Soils Classification Sheec B1
Subdivision of corrre-grained roil groups ........ B2
Values of soils ar subgrade, rubbase, or bare materials . 82
Potential frost action Bb
Compressibility and exp.naion .............. B5
Drainage characteristics 85
Compaction equipment ......,............ B6
Graphical Presentation of Soils Data .............. B7
Table B1

UNIFIFIED SOIL CIASSDICATION SYSTEM
APPENDIX B
CHARACTERISTICS - OF SOIL GROWS PERTAINING TO
RQAD3 AND AIRFIELDS
Introduction
1. The propertiee desired in eoile for foundation6 under r~ad6
and airfield6 and for base courses under flexible pavemsnte are: adequate
strength, good compact ion characteristics, adequate drainage, re -
I
sietance to fro8t action in areas where frost is a factor, and acceptable
I
compress ion and expansion characterlotice . Certain of theoe propart lee,
if inadequate in the soils available, may be supplied by proper conetruc-
tion methods, For instance, material8 having aood drainage characteristics
are desirable, but if such materiale are not available locally, adequate
drainage may be obtained by installing a properly deei~nod water collect -
ing system. Strength requirements for base course materials, to be used ial- I
uiediately under the pavement of a flexible pavement structure, are high and
only good quality materials are acceptable, H~wever, low strangthe in
subgrade materials may be compensated for in mnjp cases by Increasing
the thickness of overlying concrete ~avement or of base materials in
flexible pavement construction. Frcn the foregoing brief dfscuslion, it
may be seen that the proper design of rcade and airfield pavements requires
the evaluation of 8011 propertiee in uore detail than ie possible by uee
of the general soils claeeificetion system. However, the grouping of
soile in the claesificati.on system i8 such that a general indication of
their behavior in rcad and airfield conetruction tnay be obtained.
Features Shown on Soile Claseif ication Sheet
2. General characteristics of the soil groups pertinent to rcads ,
and airfields are pr2sented in table B1. Columns 1 through 5 how ~?aJor ,

soil divieiond, group eymbols, hatching and color sw.bol8; column 6 gives
names of so11 types; column 7 evaluates the perfonnance (strength) of the
soil groups when used as sutgrade materiale that vill not be subject to
frost action; column 8 and column 9 make R similar evaluation for the
soils when used as subbase and base mterials; potential f'roe'; action is
shown in column 10; compressibility and expansion characteristics are
shmn in column 11; column 12 presents drainage characteristics; column
13 shows types of ccmpaction eqdi~ment that perform satisfactorily on
the various soil groups; column shows ranges of unjt dry weight for
compacten soils; column 15 gives ranges of typical California Bearing
Ratio (CBR) values; and column 16 gives rarges of modulus of subgrade
reaction (k). The various features prese~ted are disclsscd in thz fol-
lowing paragraphs,
Subdivision of
coarse-pained soil groups
3. It will be noted in column 3, letter symbols, that the b?.+ir:
snil groups, GM and SM, have each been subdivided into two ,;rou:'.' :c; .e-
nated by the suffixes d and u which have been chosen to represent d~sir-
able and less desirable (undeei?able) base materials, respective2.y. Thia
,-;ubdivision applies tc rcads and airfields only and is based on field ob-
servnticn a~ld labcratory tests cr: the behavior of the soils in thebe
grouys. Basis for the su~division is the liquid iinit and plast,icity
index of the fmctioc of the soil ~assinc the i,!c, 43 sieve. The suffix
d is user. .'ne:: che iiquid licit is 25 or les~ a~:d .the plasticity index
is 5 or less; the s~ffix 3 is used ctherwise. Typic~l ay~uols for soiis
in Zhese Groups are Ofid and S4u, etc.
Values 0:' soils as subgrad>,
subbase, or base materials
4. The descriptions in co11:nns 7, &., and 5 Zive a gciiclri indlca-
tion of the suitability of the soil groups fcr use as suigrades, subbase,
or base materisls, prr,vided they arc %t s1lbjecc tc frcst actior.. In
areas where frost heavin~: is a nrotle.;.., the value of ,:aterials as su5-
gr~dec or subbo;es will be reduced, dependine cr, the potrntCal frost
actior. of the materia;, as shcwi: in ccluelr. 1;. ?roper desi&:l ; I-ccecicres

j
should be used in situations where this is a problem. The coarse-grained
, soils in general are the best subgrade, subbase, and ba~e mater:als. The
i
!
GW group haa excellent qualities as a subgrade and subba..c\, and is good
as base material. It is noted that the adJective "c:;cellentW is not
1
i
!
E I
!
used for any of the soils for base courses; it is considered that the
adjective "excellent" should be used in reference to a high quality
processed crushed stone. Poorly-graded gravels and some silty gravels,
I
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!
groups GP and Wd, are usually only slightly lees desirable as subgrade
or subbase materials, and under favorable conditions may be ueed as bese
materids for certain conditions; however, poor gradation and other factors
scuetimes reduce the 'value of such aoils to such extent that they offer
only moderate strength and therefore their value as a base material is
leoe. Th6 GML, GS, and SW groups are reasonably good subgrade material.s,
but are &enerally poor to not suitable as bases. The SP and SMd soils
csually are considered fair to gocd subgrade an9 subbase materials but
in gereral are poor to not suitable for base materials. The SKU and SC
soils are fair to poor sub~rade and subbase ma.terials, end are not suit-
able for base materials. The fine-grained soils range frcm fair to very
poor subgrade materinls as foliows: silts and lean clays (ML and CL),
fair to poor; organic silts, lean organic clays, and micaceous or diato-
uaceour soils (oL and MI), poor; fat clays and fat organic cloys (CH and
OH), poor to very poor. These qualities are ccm~ensated for in flexible
Favement design by increasing the thickness of overlyifir, bese material,
and in rigid pavemefit design by increasing the pavement tbicl~ness c;r by
the addition of a base course layer. iione of the fine-grained soils nre
suitable as suobase or base aaterials. The fibrous crganic soils (group
~ t are ) very 2oor subzrade materials and should be removed wherever pos-
sible; otherwise, s~ecial construction measures should be adcpted. They
are not suitable as sukhse and base naterials. The California Bearicg
Ratio (CER) vaiuqs showrl i:~ cokan 15 zive a relative indicatior; cf the
stre:,,y.ll of the ~ai.ious soil Groups as used in f~exjble pave~ent design.
Similarly, values of subjrade modulus (k) in cclunn 1.6 are relative ic-
dicaticns oi' strengths frcrr. plate-besrir~g tests us ~sed in rigid Favement
Jesii;n. As tkese tests ore used ;cr the design of pbver.ents, octunl

test values should be used for this purpoee inetead of the approximate
values shown in .the tabulatdon.
5. For wearing eurfaces on unsurfaced roads eand-clay-pave1 mix-
tures (GC) are generally considered the moet satisfactory . However, they
should not contain too large a percentage of fines and the plasticity In-
dex should be in the range of 5 to about 15.
Potential froet act*
6. The relative effects of frost action on the various soil groups
are ehown in :olumn 10. Regardleas of the frost susceptibility of the
various soil groupe two conditions must be present aimultaneously before
froet action will be a maJor consideration. These are a source of water
during the freezing period and a sufficient pericd for the freezing tem-
perature to penetrate the ground. Water necessary for the formation of
ice lenses may become available frotu a high ground-water table, capillary
supply, water held within t5e soil voids, or through infiltration. The
degree of ice formation that will occur in any given case is markedly in-
fluenced by environmental factors such as topographic position, st-?tifi-
cation of the parent soil, transitions into cut sectione, lateral flow
of water from side cuts, localized pockets of perched ground water, and
drainage conditions. In general, the silts and fine silty sands are the
worst offendere as far as frost is concerned. Coarse-~rained materials
with little or no fines are affected only slightly if at all, Clays (CL
and CH) are subject to frost action, but the loss of strength of such
materiala may not be as great as for silty soils. Inorganic soils con-
taining less than three per cent of grains finer than 0.02 ma in diameter
by weight are generally nonf rost-susceptible . Where frost-susceptible
soils are encountered in subgrades and frost is a definite problem, two
acceptable methods of design af pavements are available. Either a suf-
ficient depth of acceptable granular material is placed over the soils
to prevent freezing in the subgrade and thereby prevent the detrimental
effects of frost action, or a reduced depth of granular material is used,
thereby allowing freezing in the subgrade, and design is based on the
reduced strength of the subgrade during the frost-melting period. In
many cases appropriate drainage measureb to prevent the accumulation of

I
water in the roll pore8 will help to diminish ice segregation in the sub-
grade and rubbase.
Cmpreeoibility and expansion
7. Theme characterietico of soils -;ry be of two typee insofar as
their applicability to road and runway design is concerned. The firet
is the relatively long-term compreesion or coneolidation under the dead
weight of the structure, and the second is the short-term compressior,
! and rebound under moving wheel loads. The long-term consolidation of
I
soil8 becomes a factor in design primarily when heavy fills are made on
I
I
compressible 80118. If adequate provision is made for this type of
settlement during construction it will have little influence on the load-
I
! carrying capacity of the pavement. However, when elastic soils subdect
I
I
to compreseion and rebound under wheel load are encountered, adequate
protection must be provided, as even small movements of this type soil
may be detrimental to the base and weering course of pavements. It is
! fortunate that the free-draining, coarse-grained soils (GW, GP, SW, and
1
I SP), which in general make the beet subgrade and subbase materials, ex-
hibit almost no tendency t~ward high compressibility or expansion. In
general, the compressibility of soils increases with increes ing liquid
limit. The foregoing ie not ccmpletely true, a8 compressibility is also
influenced by soil strucb~re, rain shape, previous loading history, and
other factors that are not evaluated in the classification system. Un-
desirable compreseibility or expansion characteristics may be reduced by
distribution of load through a greater thickness of overlying material.
This, in general, is adequately handled by the CBR method of design for
i flexible pavements ; hovever, rigid pavements may require the addition of
an acceptable base couree unl :r the povement.
Drainaue characteristics
8. The drainage characteristics of 0011s are a direct reflection
of their permeability. The evaluation of drainage characteristic^ for
use in rcads an3 runways is shown in column 12, The presence of moisture
in base, subbase, ar~d subgrade materials, except for free-drainina, coarse -
grained soils, may cause the development of pore water pressures and loss
of strength. The moisture may come frcm infiltration of rain water or by

capillary rise from an underlying water table, While free-draining ma-
terials permit rapid draining of water, they permit rapid ingress of
water also, and if such materials are adjacent to less pervious materials
and have free access to water they may serve as reservoirs to saturate
the less pervious materials. It is obvious, therefore, that in most in-
stances adequate drainage systems should be provided. The gr~velly and
sandy scils with little or no fines (group: CM, GP, SW, and SP) have ex-
cellent drainage characteristics. The GMd and SMd groups have fair to
poor drainage characteristics, wherea~ the GMu, GC, SMu, and SC groups
may be practically impervious. Soils of the ML, MH, and Pt groups have
fair to poor drainage characteristics. All. of the other groups have poor
drainage characteristics or are practically hpervious.
Compaction equipment
9. The conpaction of soils for roads and runways, especially for
the latter, require6 thet a high degree of density be uttained at the
time cf construction in order that detrimental consolidation will not
take place a e r traffic. In addition, the dealmental effects of water
are lessened in caseG where saturation or near saturation takes place.
Processed materials, such as crushed rock, are often used as base course
and such materials require special treatment in compaction. Types of
canpaction equipment that will usually produce the desired densities are
shown in column 13. It may be noted that se%eral types of equipzent are
listed for some of the scil groups; this is because variations in soil
type within a given group may require the use of different equipment.
In some cases more than one type of equipment may be necessary to produce
the desired densities. Steel-wheeled rollers are recommended for angular
materials with limited amounts of fines , crawler-type tractors or rubber-
tired rollers for gravels and sands, and sheepsfoot rollers for coarse-
grained or fine-grained soils having some cohesive qualities. Rubber-
tired rollers are also recommended for final compaction operations for
most soils except those of nigh liquid limit (group H). Suggested mini-
mum weights of the various types of equipment are shown in note 2 of the
table. In column 14 are shown ranges of unit dry weight for soils com-
pacted according to test method 100 (cE 55 compaction effort),

MIL-sTD-~~~A, Thcse values are included primarily for guidance; desim
or control of construction should be based on test results.
Graphical Presentation of Soils Data
10, It is custcumry to present the res'jlts of soils explorations
t
e. I on drawings aa schematic representations of the borings or test pits or
! I on soil profiles with the various soils encountered shown by appropriate
1 1 symbols. As one approach, the group letter symbol (CL, etc.) may be
written in the appropriate section of the log. As an alternative, hatch-
ing symbols shown In column 4 of table B1 may be used. In addition, the
natural water content of fine-grained soils should be shown along the
i
side of the log. Other descriptive abbreviations may be used as deemed
appropriate. In certain special instances the use of color to delineate
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! soil types on maps and drawings is desirable. A suggested color scheme
to show the major soil groups is described in column 5 of table B1.
1. -
F
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