Standar d Specif ication f or
Cla ssif ic ation
of Soils and Soil-Aggr ega te Mixtures for Highway Constr uc tion Pur pose s
r uM
AASHTO Designation: M 145-91 (2008)
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l'JH
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1.
S COP E
1.1.
Tins recommended pr actice describes a pr ocedur e f or classif ying soils into seven gr ou ps based on la borator y deter m ination of par ticle size distri bution, hquid limit, and plasticity index. Evaluation of soils within each gr ou p is made by means of a "gr ou p index." which is a value calculated from an em pirical f ormula. The grou p classification, including gr ou p index, should be usef ul in deter mining the r elative quality of the soil material f or use in earthwork str uctures, pa r ticularly em bankments. subgrades. sub bases. and bases. However, f or the detailed design of im portant srr ucrures, additional data co ncer ning str ength or perf ormance ch ar acter istics of th e soil under field c on ditio ns will usually be r equir ed.
1.2.
The values stated in SI units ar e to be r egarded as the s tandar d.
2.
REFERENCED DOCUMENTS
2.1.
2.2.
A AS HTO S ta nd ard s •
R 58 , D1y Pr e par ation of Disturbed Soil and Soil-Agg r egate Sam ples for Test
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T 11, Mater ials Finer Than 75-µ111 (No. 200) Sieve in Mineral Aggr egates by Washing
•
T 27, Sieve Analysis of Fine and Coar se Agg r egates
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T 88, Par ticle Size Analysis of S oils
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T 89, Detemuniug th e Liquid Li111it of Soils
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T 90, Detenuiniug th e Plastic Limit and Plasticity Index of Soils
•
T 146 , Wet Prepar ation of Disturbed Soil Samples f or Test
AST Ja,f Sr nnd ar d : •
D 1140 , Standar d Test Methods f or Amount of Material in Soils Finer than No. 200 (75-µm) Stev e
Note
1 Eith er T 88, or T 11 and T 27, or ASTiv[ D 1140 will be used 10 deter mine th e par ticle size distri bution of soils or s oil-agg r egate mixtures as a basis f or classificatio n.
3. 3 .1.
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CL AS SIFIC ATION The classification is made by using the test Iimits and gr ou p index values shown in Table 1. If a more detailed classifi cation is desired. a further su bdivision of th e gr ou ps shown in Table I may be made. An example of th e classificatio n with su bgr ou ps such as those shown in Ta ble I 1nay be made. An exam ple of the classification with such su bgr ou ps is shown in Table 2. The liq uid limit and plasticity index ranges f or the A-4. A-5. A-6. and A-7 soil grou ps ar e shown gr a ph ically in Figur e 2 .
TS-1b
M 145-1 0
2012 b the Ame
A
f St l Highwa
and T
portati
Of fi i ls
rights reserved. Duplr canou 1s a viclanon of applica ble law.
AASHTO
Liquid hn11t U•ual
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ty pes of s,gm!icant coo,munll mato,c i.al,
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-
s,.,.... fngm,e11t,
·
gra,d ilDd
"""
w,d
Gt-ncnl ntmg as •ubgr adc •
Pbst>c,ty Uldcx o f A·7-S subgroup ,.equal IO or kss than LL - lO. Plas!LClty llldex
40 m..:IX
"=
Silty or da)cy gra,d and W>d El
ot A-74 5ltlgroup is greatff llw:L LL - 30
(Stt f ig,.R 2 )
C 20 12 by the Amfflc:m Assoc12.noo o f St:nc H,gh,,,::iy and Tnosponanoo Offic12.l, All nghts rcscr.Td Du phc::illO!I a nolanon of ap phc::i blc law ••
"= " =
"=
"=
Silty soil
•
Clayey soil
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f air to Poor
3.2.
C l a s sijieat 1011 P l " oced 11r e- \V 1t h r equir ed test data availa ble. pr oceed f rom left to r ight in Ta ble I or Ta ble 2. and the corr ect gr oup will be f ound by pr ocess of e liminatio n. The first grou p f ro m the left 11110 which the test darn will fit rs the corr ect classr fl caticn All liuunng test values ar e sho wn as whole numbers. If f r actional num ber s appear on test reports. convert to near est whole nu mber poses of ctassincano n Gr oup index values should always be shown m par entheses after f or pur gr oup sym bol as A·2·6(3). A·4 (5 ). A·6( 1.2 ). A· 7·5( 17). etc.
4.
DEFINITION S OF GRAVEL, SAND, AND SILT-CL AY
4.1.
The term s .. gravel." "Co arse sand." and -silt-clay." as detenninable f r om the minimum test data r eqmr ed 111 tlus ctassuicnnon arr ang emen t and as used m su b seq u ent wor d de scr i pt ions. ar e defined as f ollo ws
4.1.1 .
g rar e/-mate nal passing sreve with 75·mm (3·in.) square openings and retained on the 2.00·mm (No I 0) sreve
4.1.2.
coar se :sa nd-material passmg the 2.00 ·mm (No 10) sreve and retamed on the 0.425·mm ( No. 40) steve .
4.1.3.
4.1.4. 4.1.5.
4.1.6.
5. 5.1. 5.1.1.
fine sa11d -matenal passing the O 425-mm ( No. 40) siev e and rer aiued on the 75-11111 (No. 200 ) sieve. stlt -cla y ( combmed sitt and c/a y)- ma te r ial pass mg the 75 ·1u11 (No. 200 ) siev e. Boulder s and co bbles (r etained on 75·mm (3·in.) sie, e) should be excluded f rom the por tion of the sample to which the cla ssification is ap plied. but the percentage o f such mate nal. if any. in the sample should be r ecor de d. The ter m . . silty" is applied to fine material having plasticity mdex of IO or less. and the ter m "clayey" is ap plied to fine mater ial having plasticity ind ex of 11 or gr ea ter
DE SC RIPTION OF C L ASS IFIC ATION GROUPS 1 ar Matena/:s-Conta uung 35 percent or l e ss passing 75 ·11111 (No. 200) sieve (Note 2). Gra 111 /
Gr ou p A- /-The typical material of th is gr ou p is a well-graded mixture of stone fragments 0 1 gr avel. coarse sand. fine sand. and a nonplnsnc or feebly plastic soil bmder . However . this gr oup also mcludes stone fragments. gravel. coar se sand. volcanic cinder s. etc .. without soil bind er .
5.1.1.1.
Subgrou p A- J -a mcludes those materials consisting pr edominantly of stone f ragments or g r ave l. either with or wruicm a well-graded binder of fine material.
5.1.1.2.
subgroup A-1-b mcludes those materials consisting pr edominantly of coarse sand. either " ith or without a well-graded soil binder .
5.1.2.
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Gr ou p A-3- The typ ical material of this gr oup is fine beach sand or fine deser t blow sand witho ut silty or clay f mes or with a very small amount of nonplasttc silt. The gr oup in clude s also str eam de posited mixtur es of poor ly graded fine sand and limit ed amounts o f coarse sand and gravel. •
M 145-3 C 2012 by the An>mcan Assoct::11100 cf State Highway aud Tr a11s pon:::111on Offi ci::i ls. AU nghts reserved, Duphcallon rs i nol::1t1on oh pphcable law
AAS HTO
5.1.3.
Group A-l TI1is group includes a wide , ar te ry of "granular" materials that ar e bor der line between the matenals f alling in Groups A-1 and A-3 and silt-clay materials of Gr oups A--1. A-5. A·6. and A-7. It mcludes all materials containing 35 percent or less passmg the 75-Jtm (No. 200) sieve mat cannot be classified as A-1 or A-3 due to fines content or plasticity or borh. in excess of the limitations f o r those gr ou ps.
5.1.3.1
Su bgr oups A·2·4 and A·2·5 include various gr anu lar mater ia ls couta ming 35 per cent or less passing the 75-Jnll (No 200 ) sieve and With a minus 0.425-mm (No 40) por tion having the character isucs of the A ·-1 and A-5 groups. These gr ou ps include such matenals as gr avel and coarse sand with silt contems or plasticity indexe s in excess o f the linutattons of Group A-1 . and fine sand ,, ith non plastic silt comem i.n excess of the limitations of Grou p A-3.
5.1.3.2.
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Su bgroups A·2·6 and A·2· 7 include materials snnilar to those descri bed under Su bgr oups A·2·4 and A·2·5 except that the f ine ponion contains plastic clay having the characteristics of die A-6 or A-7 gr oup.
Note 2---Classification of materials in the various gr oups a p plies only to the fraction passing tile 75-m m (3·ll 1.) sieve T her ef or e. any s pe cr flcauons r egar ding the use of A· I. A-2. or A-3 mater ials i.J1 constm ction should state whether boulder s retamed on the 75-m m (3·in) sr ev e are pennitted
5.2. 5.2.1.
S 1l 1-C l a y M ar enal s---C o111aiJ 1in g more than 35 percent passing the 75·11m (No. 200) sieve.
cr oup A-4-The typical material of this gr oup is a nonplastic or moder ately plastic silty soil usually havi ng the 75 percent or more passmg the 75-iun (No. 200) sieve TI 1e gr ou p includes also mixtur es of fine silty soil and up to 6-1 percent of sand and gravel retained on i5·11m (No. 200) sieve.
5.2.2.
ibed under Grou p A·4. 1 A-5-The typical material of this gr oup is similar to that de scr G r o1 p exce pt that n rs usually of diatomaceous or micaceous character and may be highly elastic as indicated by the high liquid limi t.
5 .2 . 3 .
G r ou p A -� The typ ica l material of this group is a plastic clay soil usually having 75 per cent or mor e passing the 75-iuu (No. 200) sieve. The gr oup also includes mixtur es of f me clayey soil and u p to 64 percent of sand and gr a vel r etained on the i5-1uu (No. 200) sieve. Materials of tlus g r ou p usually haw tugh-vo lume change between wet and dr y states.
5.2.4.
G r oup A- 7-The typical material of this group rs similar to that descri bed wide r Gr oup A·6. except that it has the lugh liquid limits character istic of the A-5 gr oup and may be elastic as well as sub ject to high-volume change.
5.2.4.1.
Su bgrou p A- 7-5 includes those materials with moderate plasticity indexes in r elation to liqmd limit and winch may be highly elastic as "ell as su b ject to considera ble volume c hange.
5.2.4.2.
Subgroup A· 7-6 include s those materials with hrgh plasticity mdexes in relation to liqmd Jinu t and which are sub j ect to extremely high-volume c hange.
Note 3-Highly or ganic soils ( peat or muck ) may be classified in an A·8 gr oup. Classification of these mateiials is based on visual ins pection. and is not dependent on per centage passing the iS ·1u11 (No. 200) sieve. liquid li mit. or plasticity mdex The material is co m po sed pr imanly of partially decayed orgnmc matter . gener ally has a fibr ous text me. dmk br own or black color . and an odor of decay. These or ganic matenals ar e unsuitable f or use i.J1 e m ba nk me ms and subgrades. TI 1ey ar e high ly com pr essi ble and have lo w str ength.
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AASHTO
6.
GROUP IN DEX
6.1.
The grou p ind ex ts calculated fr om the f ollo wing f o rmula: Group mdex = ( F 35) (0.2
-
+ 0.005
( U - -1 0))
+ 0.01
( F 15) ( P I 10)
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-
wher e :
F
percentage passing 75·11111 (No. 200) sieve. ex pr essed as a whole num ber . This percentage is based only on the matenal passing the 75-m m (3·111.) sieve.
U
liquid limit. and
PI
plasticity index.
6.1.1.
when the calculated group index is negative. the gr ou p index shall be repor ted as zer o.
6.1.2.
The gr ou p index should be r eported to the near est whole num ber .
6.2.
Figur e I may be used 111 estimatmg the gr oup mdex. by determuung the partial gr ou p index due to liquid lunit and that due to ptesnciry index. then o btaining the total of the rwc partial grou p indexe s.
6.3.
When calculating the grou p index of A-2-6 and A-2-7 su bgroups. only the PI ponion o f the f ommla (or of Figure 1) shall be used.
6.4.
The f ollowing a 1 e examples of calculations o f the gr ou p ind ex:
6.4.1.
Ass ume that an A·6 mater ial has 55 per cent passing t he i5·µm (No 200) sieve. liquid limit of 40. and plasticity index of 2 5. Th en. Group index= ( 55
6.4.2.
35) [0.2
+ 0.005
(40 - 40)]
+ 0.01
( 55
-
15) (25 - 10) = 4.0
+ 6.0
= 10
Assume that an A·i material has 80 percent passing the i5·)Ull (No. 200) sieve. hquid limil of 90. and plasticity mdex of 50. TI1en. Gr ou p index
6.4.3.
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•
(80- 35) (0.2
+ 0.005
(90 - 40)]
+ 0.01
(8 0- 15) (50- 10)
•
20.3
+
26.0. or 46.3
Assume that an A·4 material has 60 percent passing t he i5·111n (No. 200) sieve. liqu id li11111 of 2 5. and plasticity index of I. The n. Group index= (60- 35) [0. 2 + 0. 005 (25 - .JO )]+ 0.01 (60 - 15)(1 - 10) = 25 x (0.2 - O.Oi5) + 0.01 (45) (-9) = 3.1 - 4.1 = - 1.0 Report as z ero.
6.4.4.
Assume that an A-2- i material has 30 per cent passing the i5-r nn (No. 200) sieve. liquid lim it of 50. and plasticity index of 3 0. Then. Group index= 0.01 (30- 15)(30 - 10) = 3 0 or 3 (Note that only the PI portion of f o mmla was used)
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M 145-5 C 2012 by tht Amm tlll A«oc1:: mon of Statt Highway :md Tr :on , pon ::mon Officials All nghts r eserved Dupbcauon 1s a ,.,ol:auon oh pplitabk bw
AASHTO
Gr oup Index (GI) (F - 35) (02 + 0.005 (LL - 40)] + 0.D1 ( F - 15 ){ Pl 10) where F'"' Pe rcent Passing 75-µm sie w, LL: Liquid Li mit, and P l ,. Pl asti::ty Index. •
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�n wcrting wilh A·2·6 and A·2· 7 Subgr
�n the oofTOned Partial Group Indices are negative, the Gr oup Index shot.*t be r eportod as zer o.
•
30
50
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N
.;
z
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� �
"8''
.[,,
,
""
e,
e
� .
...l
20
i!' •
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� 70
$' I"
i r t
"
" ,G> / ,@
"" 80
,!'
10
"" 90
.. •
100 Ex8ffl)le: 82 Percent Passrtg 75-µrn Sieve LL : 38 P l 21 •
Thone PGI"' 8.9 f or LL PGI = 7.4 f or Pl
GI
•
16
Figur e 1-Gr oup Ind ex Chart
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M 145-6
AASHTO
C 2011 by !ht Amtnca.n Associalton of Sutt Highway and Tr.m� pona !ton Official. All nghts rtst1' td Du phcauon t s a no bnon of app hcab k bw
•
70
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/ 60
/
I/
50
Ii>
/
s>
,t,* '/ /
A-7-f;
30
I/
/
"' e-a-e
20
/
A-7-5
/ A-2 -7
10
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A-5
�2..£,
"72+5
0
0
20
30
40
50
60
70
80
90
100
LqLid l.J mrt
�
A-2 Soils rom.un l=lh.m 35 poroe m fine,-lh.m dr 7S..µm(So 200)san�
Figur e 2 -Liquid Limit and Plasticity Index R anges f or Silt-Clay Mater ials
7.
BASIS FOR GROUP INDEX FORMU L A
7.1.
The em pirical gr ou p index f ommla devised f or a p pro ximately within-gr o up evaluation of the ..clayey granular materials .. and the -si jr -clay materials" is based on the f ollow mg: assum ptions:
7.1.1.
Mater ials f alling within Gr ou ps A-l·a. A-1- b. A·2·-t A-2-5. and A-3 ar e satisf actory as subgrade when pr o per ly drained and com pacted under moder ate thickness pavement ( base and/or sur f ace course) of a type suitable f or the traf fi c to be cam ed. or can be made satisf actor y by additions of small amounts of natur al or artificial binders.
7.1.2.
l\later ials f alling wuhut the ..clayey granular " Gr ou ps A·.2·6 and A·.2· 7 and the -silt-clay" Gr oups A·4. A·S . A·6. and A·7 will range in quality as subgrade fr om the n p pr oxunate equrvnlent of the good A·.2-4 and A·2·S su bgrades to f air and poor su bgrades r equiring a layer of sub base mater ial or an incr eased thick ness of base course over that r equir ed under Section 7.1. 1 111 or der to furnish adequate su p pon f or traffic loads.
7.1.3.
The assumed cnucat minimum percentage passing the 7S·)tm (No 200) sreve rs 35 negtecr mg plasticity. and I S as aff ected by plasticity mdexes greater than 10
7.1.4.
Liquid Iinurs of 40 and a bove ar e assumed to be cntical
7.1.5.
Plasticity indexes of IO and above are assumed to be cnncal.
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AASHTO
