Manual de Pruebas de Campo Para Acapulco- Oroo

8/12/2019 Manual de Pruebas de Campo Para Acapulco- Oroo

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Chapter 3

ENGINEERING CLASSIFICATIONAND DESCRIPTION OF SOIL

General

Application

Soil investigations conducted for engineering purposest ha t use test pits, t renches, a uger a nd dr ill holes, or ot her

explora tory meth ods a nd surfa ce sam pling a nd m a ppingare logged and described according to the Unified SoilCla ssif ica t ion S yst em (U SC S) a s present ed in B ureau ofRecla ma t ion (Recla ma tion) sta nda rds U S B R 5000 [1] a nd5005 [2]. Also, bedr ock ma t eria ls w ith t he engin eeringproperties of soils are described using these standards(cha pter 2). The Recla ma t ion sta nda rds a re consist entw ith t he America n S ociet y for Testin g Ma t eria ls (AS TM)D esigna t ion D 2487 a nd 2488 on t he U S C S syst em [3,4].Descriptive cri teria and terminology presented areprima ri ly for t he visua l classif ica t ion a nd ma nua l tests .The ident ifica t ion port ion of t hese meth ods in a ssign inggroup symbols is l imited to soil particles smaller than3 inches (in) (75 millimeters [mm]) and to naturallyoccurr ing soils. P rovisions a re a lso ma de t o estima t e t he

percenta ges of cobbles a nd boulders by volume. Thisdescriptive system may also be applied to shale, shells,crushed rock, and other materials if done according tocriteria est a blished in th is sect ion. C ha pter 11 a ddr essest he logging form a t a nd cri teria for describing soil in t estpits, t renches, a uger holes, a nd d rill hole logs.

All investiga t ions a ssocia t ed wit h la nd cla ssifica t ion forirriga t ion suita bili ty , da t a collect ion, a na lyses of soiland subst ra tum mater ia ls re la ted to dra inage inves-t iga t ions , a nd Quat erna ry s t ra t igraphy (e.g ., faul t a ndpa leoflood st udies) a re logged a nd described using t he


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U .S. D epa rt ment of Agricultur e terminology outl ined inappendix I to Agr i cul tu r e H and book N o. 436 (Soi l Taxonomy), da t ed D ecember 1975 [5].

All soil classification descriptions for particle sizes lesst ha n No. 4 sieve size a re t o be in m etric units.

Performing Tests and Obtaining DescriptiveInformation

The U S C S g roups soils a ccord ing t o pot ent ia l engin eeringbeha vior. The descriptive inform a t ion a ssists w ith esti-mating engineering propert ies such as shear st rength,compr essibility , a nd perm ea bilit y. These guidelines ca nbe used not only for ident ifica t ion of soils in th e field buta lso in t he office, la bora t ory , or w herever soil sa mples a reinspect ed a nd described.

Laboratory classification of soils [1] is not alwaysrequ ired but sh ould be perform ed a s necessa ry a nd can beused a s a check of visua l-ma nu a l met hods. The descrip-tors obtained from visual-manual inspection providevaluable information not obtainable from laboratorytest ing. Visual-manual inspect ion is a lways required.The visual-manual method has part icular value inident ifying a nd gr ouping simila r soil sa mples so t ha t onlya minimum num ber of la bora tory t ests a re required forposit ive soil cla ssifica t ion. The a bilit y t o ident ify a nddescribe soils corr ect ly is lea rn ed more rea dily und er th eguida nce of experienced personnel, but ca n be a cq uired bycompa ring la bora t ory t est r esult s for t ypica l soils of eachty pe w ith their visua l a nd ma nua l cha ra cter ist ics. Whenidentifying and describing soil samples from an area orproject , a ll t he procedures need not be follow ed. S imila rsoils m a y be gr ouped t ogether; for exa mple, one sa mpleshould be ident ified a nd described complet ely, w ith t heothers identified as similar based on performing only afew of the identification and descriptive procedures.


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SOIL

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D escriptive inform a t ion sh ould be evalua t ed a nd r eport edon every sa mple.

The sa mple used for cla ssifica t ion m ust be representa t iveof the s t ra tum and be obta ined by an appropr ia te ac-cept ed or st a nda rd procedure. The origin of the ma t erialmu st be corr ect ly ident ified. The origin descript ion ma ybe a boring n umber a nd d ept h a nd/or sa mple num ber, ageologic stratum, a pedologic horizon, or a locationdescript ion with respect to a permanent monument , agrid system, or a sta t ion num ber a nd offset .

Terminology for Soils

D efinit ions for soil cla ssifica t ion a nd description a re inaccordance with USBR 3900 Standard Defini t ions ofTerm s a nd S ym bols Rela t ing t o S oil Mecha nics [6]:

Cobbles and boulders pa rt icles r eta ined on a 3-inch(75-mm ) U .S . St a nd a rd sieve. The follow ing t erm inologydistingu ishes betw een cobbles a nd boulders:

Cobbles particles of rock that will pass a 12-in(300-mm ) sq ua re opening a nd be ret a ined on a 3-in(75-mm) sieve.

Boulders particles of rock that will not pass a12-in (300-mm ) sq ua re open ing .

Gravel pa rt icles of rock t ha t w ill pa ss a 3-in (75-mm )sieve a nd is ret a ined on a No. 4 (4.75-mm ) sieve. G ra velis furt her subdivided a s follow s:

Coarse gravel pa sses a 3-in (75-mm ) sieve a nd isret a ined on 3/4-in (19-m m ) sieve.

Fine gravel pa sses a -in (19-mm ) sieve a nd isret a ined on No. 4 (4.75-m m) sieve.


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Sand pa rt icles of rock t ha t w ill pa ss a No. 4 (4.75-mm )sieve a nd is r et a ined on a No. 200 (0.075-mm or 75-m icro-met er [m]) sieve. S a nd is furt her subd ivided a s follow s:

Coarse sand pa sses No. 4 (4.75-m m) sieve a nd isret a ined on No. 10 (2.00-m m) sieve.

Medium sand pa sses No. 10 (2.00-m m) sieve a ndis r et a ined on No. 40 (425-m ) sieve.

Fine sand passes No. 40 (425-m) sieve and isretained on No. 200 (0.075-mm or 75-m) sieve.

Clay pa ss es a No. 200 (0.075-m m or 75-m ) siev e. S oilha s pla s t icity w i th in a ra nge of wa ter contents a nd ha sconsidera ble st rengt h w hen a ir-dry . For cla ssifica t ion,cla y is a fine-gra ined soil, or t he fine-gra ined port ion of a

soi l, w ith a pla st ici ty index great er tha n 4 a nd t he plot ofpla st icity ind ex versus l iquid l imit fa lls on or a bove the" A" -line (figur e 3-5, la t er in t his cha pt er).

Silt pa sses a No. 200 (0.075-m m or 75-m ) sieve. S oilis nonplast ic or very sl ight ly plast ic and that exhibi tsl it t le or no st r ength wh en a ir-dry is a si lt . For

classification, a si l t is a fine-grained soil , or the fine-gra ined port ion of a soil, wit h a pla st icity index less tha n4 or t he plot of pla st icity index versus l iqu id l imit fa llsbelow t he " A" -line (figur e 3-5).

Organic clay cla y w ith sufficient orga nic cont ent t o in-fluence t he soil propert ies is a n orga nic cla y. For cla ssifi-ca t ion, a n orga nic clay is a soi l t ha t w ould be classif ied a sa cla y except t ha t i t s l iqu id limit va lue a fter oven-dry ingis less than 75 percent of i ts l iquid l imit value beforeoven-drying.


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Organic silt silt w ith sufficient orga nic cont ent t o in-flu-ence th e soil propert ies. For cla ssifica t ion, a n org a nicsi lt is a soi l th a t w ould be classif ied a s a si lt except th a ti ts l iquid l imit value after oven-drying is less than75 percent of it s liqu id limit va lue before oven-dr yin g.

Peat ma t eria l composed prima rily of veget a ble t issuesin various stages of decomposit ion, usually with an or-ganic odor, a dark brown to black color, a spongy con-sistency, and a texture ranging from fibrous to amor-phous. Cla ssifica t ion procedures ar e not a pplied to pea t .

Classifications of Soils

Group Names and Group Symbols

The ident ifica t ion a nd n a ming of a soil ba sed on result s

of visua l an d ma nua l tests is present ed in a subsequentsect ion. S oil is given a n ident ifica t ion by a ssigning agroup sym bol(s) a nd group na me. Im port a nt informa t ionabout the soi l is added to the group name by the term" w it h" w hen a ppropria t e (figu res 3-1, 3-2, 3-3, 3-4). Thegroup name is modified using with to stress othersignifica nt component s in th e soil.

Figure 3-2 is a flow cha rt for a ssigning ty pica l na mes a ndgr oup sy mbols for inorga nic fine-gr a ined soils; figure 3-3is a flow cha rt for orga nic fine-gra ined soils; figure 3-4 isa flow cha rt for coa rs e-gra ined soils. Refer to t a bles 3-1a nd 3-2 for t he basic group na mes wit hout modifiers. Ift he soil ha s properties w hich do not dist inctly pla ce it in


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FIELD MANUAL

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FINE-GRAINED SOILS

Sandy BASIC

GROUP NAME

with sand

Gravelly with gravel

COARSE-GRAINED SOILS

with silt BASIC

GROUP NAME

with sand

with clay with gravel

Figure 3-1.Modifiers to basic soil group names(for visual classification).

a specific group, bord erline sym bols ma y be used. Thereis a dist inction between du al symbol s a n d border l ine symbols .

Dual Symbols. Dual symbols separated by a hyphen

a re used in la bora t ory cla ssifica t ion of soils a nd in visua lclassif icat ion when soi ls are est imated to contain10 percent fines. A dua l sym bol (t w o sym bols sepa ra t edby a hyphen, e.g. , GP-GM, SW-SC, CL-ML) should beused to indicate that the soil has the properties of aclassif ica t ion w here tw o symbols a re required. D ua l sym-bols are required when the soi l has between 5 and12 percent fines from la bora t ory t ests (t a ble 3-2), or finesa re est ima ted a s 10 percent by visual classif ica t ion. D ua lsymbols are a lso required when the l iquid l imit andplasticity index values plot in the CL-ML area of thepla st icity cha rt (figure 3-5, la t er in th is cha pter).


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2 3

Figure 3-2.Flow chart for inorganic fine-grained soils, visual method.


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2 4

Figure 3-3.Flow chart for organic soils, visual method.


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2 5

Figure 3-4.Flow chart for coarse-grained soils, visual method.


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Ta ble 3-1.B a sic group na mes, prima ry groups

C oa rse-gra ined soils F ine-gra ined soils

G W - Well gra ded gra velG P - P oor ly gr ad ed gr av elG M - S i lty g ra velG C - C la y ey gr a vel s a n dSW - Well graded sandS P - P oor ly gr a ded sa n dS M - S ilt y sa n dS C - C la yey sa n d

C L - L ea n cla yML - S iltOL - Orga nic clay (on or

a bove A-line- Orga nic silt (below A-line)

C H - F a t cla yMH - E la st ic siltOH - Organ ic clay (on or a bove

A-line)- Orga nic silt (below A-line)

B a sic group nameha tched a rea on P last ici ty Ch a rt(La bora tory C lassifica tion)

C L-ML - S ilt y cla yG C-G M - S i lty, clayey g ravelS C -S M - S ilt y, cla y ey s a n d

Ta ble 3-2.B a sic group na mes, 5 t o 12 percent fines(La bora tory Cla ssifica tion)

G W-G M - Well gra ded gra vel w it h siltG W-G C - Well gra ded gra vel w it h cla y (if fin es =

C L-ML) Well gra ded gra vel w ith silty clayG P -G M - P oor ly gr a ded g ra v el w it h siltG P -G C - P oor ly g rad ed g rav el w i th clay (if fin es =

CL -ML) P oorly gra ded gra vel w ith silty clayS W-S M - Well gra ded sa nd w ith siltSW-SC - Well g raded sand wi th clay (if f ines = CL-ML)

Well gra ded sa nd w ith silty clayS P -S M - P oorly gra ded sa nd w it h silt

S P -S C - P oor ly g rad ed s an d w i th clay (if fin es = CL -ML) P oorly gra ded sa nd w ith silty cla y


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Borderline Symbols. Borderline symbols are usedw hen soil propert ies indica t e th e soil is close to a noth ercla ssifica t ion group. Tw o sym bols sepa ra t ed by a sla sh,such a s C L/C H , S C /C L, G M/S M, C L/ML , sh ould be usedto indicate that the soi l has propert ies that do notdist inctly pla ce t he soil int o a s pecific gr oup. B eca use th evisual classification of soil is based on estimates ofpa rt icle-size dist ribution a nd pla st icity cha ra ct erist ics, i tma y be difficult t o clea rly ident ify th e soil as belonging t oone ca t egory. To indica t e t ha t t he soil ma y fa ll int o oneof t w o possible ba sic groups, a borderline symbol ma y beused w i th the tw o symbols separa ted by a s lash . Aborderline classification symbol should not be usedindiscrimina t ely. E very effort should be ma de first topla ce th e soil int o a single group. B orderline symbols ca nalso be used in laboratory classification, but lessfrequently.

A borderline symbol ma y be used w hen t he percent a ge offines is visua lly est ima t ed to be betw een 45 a nd 55 per-cent . One sym bol should be for a coa rs e-gra ined soil w ithfines a nd t he ot her for a fine-gra ined soil. For exa mple:G M/ML , C L/S C .

A borderline symbol ma y be used w hen t he percent a ge ofsand and the percentage of gravel is est imated to bea bout t he sa me, for exa mple, G P /S P , S C /G C , G M/S M. Itis pra ct ica lly impossible t o ha ve a soil t ha t w ould ha ve aborder line sy m bol of G W/S W. H owever, a border linesymbol may be used when the soil could be either wellgr a ded or poorly gr a ded. For exa m ple: G W/G P , S W/S P .

A bord erline sym bol ma y be used w hen t he soil could beeith er a silt or a cla y. For exa mple: C L/ML, C H /MH ,S C /S M.


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A borderline symbol ma y be used w hen a fine-gra ined soilha s propert ies a t t he bounda ry betw een a soil of low com-pressibili ty a nd a soil of high compressibil it y. Forexa m ple: C L/C H , MH /ML .

The order of the borderline symbol should reflect simi-la ri ty t o surr ounding or a dja cent soils. For exa mple, soilsin a borrow a rea ha ve been predomina nt ly ident i f ied asCH . One sa mple ha s the borderl ine symbol of CL a ndCH . To show simila r i ty to th e a dja cent CH soils , th eborder line sym bol sh ould be CH /C L.

The group name for a soil with a borderline symbolsh ould be th e group na me for t he first sym bol, except for:

C L/C H - lea n t o fa t cla yML /C L - cla yey s iltC L/ML - silt y cla y

Preparation for Identification and VisualClassification

A usually dark-brown to black material composedprima rily of veget a ble t issue in va rious st a ges of decom-posi t ion w ith a f ibrous t o am orphous t extur e a nd orga nicodor is a highly organic soil and classified as peat, PT.P lan t forms ma y or ma y not be rea di ly recognized. Ingenera l , th e grea ter t he orga nic cont ent , the grea ter t hewater content, void ratio, and compressibil i ty of peat.Orga nic soils a re oft en ident ified by t heir odor. To checkfor organic content, the soil can be subjected to thela bora t ory cla ssifica t ion liquid l imit t est cri teria . Orga nicsoils can also be identified through laboratory loss-on-ignit ion tests . Ma teria ls ident i fied as pea t a re not sub-ject ed t o th e follow ing ident ifica t ion procedures.


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S oil ident ifica t ion procedures a re ba sed on t he minu s 3-in(75-m m ) pa r t icle sizes. All plus 3-in (75-m m ) pa r t iclesmust be manually removed from a loose sample, orment a lly for a n int a ct s a mple, before cla ssifying t he soil. E st ima t e a nd n ot e th e percent by volume of t he plus 3-in(75-mm ) pa rt icles, bot h t he percent a ge of cobbles a nd t hepercent a ge of boulders.

Not e: B eca use t he percent a ges of t he pa rt icle-size distribution in laboratory classification(AS TM: D 2487) a re by dry w eight a nd th eest imates of percentages for gravel , sand, andfines are by dry weight, the description shouldstate that the percentages of cobbles andboulders are by volume, not weight, for visualcla ssifica t ion. E st ima t ion of the volume of cob-bles a nd boulders is not a n easy t a sk. Accura teestim a t ing req uires experience. While exper-

ienced loggers may be able to successfullyest imate the minus 3-in fract ion to within5 percent , th e ma rgin of error could be la rg er foroversize pa rt icles. E st ima t es ca n be confirmedor cal ibrated with large scale f ie ld gradat iont ests on cri t ica l project s. G iven th e la rge pos-sible errors in these est imates, the est imatesshould n ot be used a s t he sole ba sis for d esign ofprocessing equipment. La rge sca le gra da t ionsshould be obt a ined a s pa rt of th e process pla ntdesigns.

In most cases, the volume of oversize is estimated inthree size ranges, 3 to 5, 5 to 12, and 12 inches andla rger. Cobbles a re often divided int o t w o size ra nges,because in roller compacted fill of 6-in compacted liftt hickness, t he ma ximum size cobble is 5 inches. If t hepurpose of the investigation is not for roller compactedfill , a single size ra nge for cobbles can be est ima t ed.


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Estimate and note the percentage by dry weight of thegra vel, sa nd, a nd fines of th e fra ct ion of t he soil sma llert ha n 3 in (75-mm ). The percenta ges a re est ima t ed to t heclosest 5 percent . The percent a ges of gr a vel, sa nd , a ndfines must add up to 100 percent, excluding tracea mount s. The presence of a component n ot in sufficientquantity to be considered 5 percent in the minus 3-in(75-mm ) port ion, is indica t ed by t he term " t ra ce." For ex-a mple: t ra ce of fines. A t ra ce is not considered in t het ot a l of 100 percent for t he component s.

The first step in the identification procedure is todetermine the percentages of fine-grained and coarse-gra ined ma t eria ls in t he sa mple. The soil is fine-gra inedif it cont a ins 50 percent or more fines . The soil is coa rs e-grained if i t contains less than 50 percent fines.P rocedures for t he description a nd cla ssifica t ion of t heset w o prelimina ry ident ifica t ion groups follow .

Procedures and Criteria for Visual Classificationof Fine-Grained Soils

Select a representat ive sample of the materia l forexaminat ion and remove part ic les larger than theNo. 40 sieve (medium sa nd a nd la rger) unt i l a specimenequiva lent t o a bout a ha ndful of represent a t ive ma teria lis a va ila ble. U se t his specimen for performing t heident ifica t ion test s.

Identification Criteria for Fine-Grained Soils. Thet ests for ident ifying propert ies of fines a re dry strength ,dilatency , toughness , and plasticity .

1. D r y st r en g t h . S elect from t he specimen enoughmaterial to mold into a ball about 1 in (25 mm) indiam eter. Mold or w ork the ma teria l unt i l i t ha s theconsist ency of put t y, a dding w a t er if necessar y.


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From t he molded ma ter ia l , ma ke a t lea s t t hree tes tspecimens. E a ch test specimen should be a ba ll ofma teria l a bout in (12 mm) in diam eter. Allow t het est specimens to dry in a ir or sun, or dry by a rt ificia lmea ns, a s long a s t he tempera t ure does not exceed60 degrees Cent igra de ( E C ). In m ost ca ses, i t w ill benecessa ry t o prepa re specimens a nd a l low th em t odry over night . I f the test specimen cont a ins nat ura ldry lumps, those th a t a re about in (12 mm) india met er ma y be used in pla ce of molded ba lls. (Theprocess of molding and drying usually produceshigher s t rengths t ha n a re found in na tura l dry lumpsof soil). Test t he st reng t h of t he dry ba lls or lum ps bycrushing them between the f ingers and note thestrength as none, low, medium, high, or very higha ccording to t he cri t eria in t a ble 3-3. If na t ura l drylumps a re used, do not use th e results of an y of t helumps t ha t a re found t o cont a in par t icles of coa rse

sa nd .

Ta ble 3-3.C rit eria for d escribing d ry st reng t h

None The dry specim en crumbles w it h merepressure of ha ndling.

Low The dry specim en crum bles w it h som efinger pressure.

M ed iu m Th e d ry specim en br ea k s in t o pieces orcrum bles w ith considera ble fingerpressure.

H igh The dry specimen ca nnot be broken w it hfinger pressure. S pecimen will brea k int o

pieces betw een t humb a nd a ha rd surfa ce.

Very High The dry specimen ca nnot be brokenbetw een th umb an d a ha rd surfa ce.


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The presence of high -st rengt h, w a t er-soluble cemen t -ing ma teria ls , such a s ca lcium ca rbona te , ma y ca useexcept iona lly high dry st reng t hs. The presence ofca lcium ca rbona t e ca n usua lly be detect ed from t heintensit y of the r ea ct ion w ith dilute hydr ocloric a cid(H Cl). Cr i ter ia for react ion w ith H Cl a re present edin a subsequent pa ra gra ph.

2 . D i l a t a n c y. Select enough materia l f rom thespecimen t o mold int o a ba l l a bout in (12 mm) indiam eter. Mold th e ma teria l , a dding w a ter if neces-sa ry, unt i l i t ha s a soft , but not st icky, consistency.Sm ooth th e soi l ba l l in the pa lm of one ha nd w ith t hebla de of a knife or spat ula . S ha ke horizont a l ly (th esoil ball) , striking the side of the hand vigorouslya ga inst the oth er ha nd severa l t imes. Note thereact ion of th e wa ter a ppearing on th e surfa ce of th esoil. S q ueeze t he sa mple by closing t he ha nd or

pinching the soil between the fingers and notereaction as none, slow, or rapid according to thecriteria in ta ble 3-4. The reaction cri teria a re thespeeds w i th w hich w a ter a ppea rs w hi le shaking anddisa ppea rs w hile squ eezing.

Ta ble 3-4.C rit eria for describing dila t a ncyN on e N o visible ch a n ge in t h e s pecim en .

S low Wa t er slow ly a ppea r s on t he sur fa ce of t h especimen during sha king a nd does not disa p-pea r or disa ppea rs slow ly upon sq ueezing.

Ra pid Wa t er qu ickly a ppea rs on t he surfa ce of t he

specimen dur ing sha king a nd disa ppearsupon sq ueezing.


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3 . Toughness . Following completion of thedi la ta ncy test , t he specimen is sha ped into a nelonga t ed pat a nd rolled by ha nd on a smooth surfa ceor be tween the pa lms in to a thread about c in(3 mm ) dia met er. (If t he sa mple is too w et t o rolleasi ly, spread the sample out into a thin layer anda l low some w a ter loss by eva pora t ion). Fold thesa mple threa ds a nd rerol l repeat edly unt i l th e threa dcrumbles a t a d ia meter of a bout c in (3 mm) whenth e soi l is nea r the plast ic l imit . Note the t imerequired to rerol l the thread to reach the plast iclimit . Not e t he pressure requ ired t o roll t he t hr ea dnea r t he pla st ic l imit . Also, note t he st rengt h of t het hrea d. After t he thr ea d crum bles, the pieces shouldbe lumped together and kneaded unt i l the lumpcrum bles. Not e t he t oughn ess of t he ma t erial duringkneading.

Describe the toughness of the thread and lump aslow, medium, or high according to the cri teria intable 3-5.

Ta ble 3-5.C rit eria for describing t ough ness

Low Only slight pressure is req uired to roll t he

th rea d nea r the plast ic l imit . The th rea da nd the lump are wea k and sof t .

Medium Medium pressure i s required to rol l theth rea d to nea r th e pla st ic l imit . The th rea da nd t he lump ha ve medium st i ffness.

H igh C on sid er a ble pr essur e is r eq uir ed t o r oll t heth rea d to nea r th e pla st ic l imit . The th rea da nd t he lump ha ve very high st i ffness.


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4 . P l a s t i c i t y. On t he basis of observa t ions m a deduring t he toughness t est , describe t he pla st icity ofthe materia l according to the cr i ter ia given int a ble 3-6 (figur e 3-5).

Ta ble 3-6.C rit eria for describing plas t icity

Nonpla st ic A 3-mm t hread ca nnot be rolled a t a nyw a ter content .

Low The th rea d ca n ba rely be rol led, a nd th elump ca nnot be formed w hen drier t ha nt he pla st ic l imit .

Medium The t hrea d is eas y t o roll , a nd not mucht ime is required t o rea ch t he pla st ic l imit .The t hr ead ca nnot be rerolled a fterrea ching th e pla st ic l imit . The lumpcrumbles w hen drier t ha n t he plast iclimit .

H igh I t t a kes considera ble t ime rolling a ndknea ding to rea ch th e pla st ic l imit . Theth rea d ca n be rol led severa l t imes a f terrea ching th e pla st ic l imit . The lump ca n

be form ed wit hout crum bling w hen drierth a n th e pla st ic l imit .

After the dry st rength, di la tency, toughness, andplasticity tests have been performed, decide onwhether the soil is an organic or an inorganic fine-

gra ined soil.


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Figure 3-5.Plasticity chart.


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Identification of Inorganic Fine-Grained Soils.Classify the soi ls using the resul ts of the manual testsa nd t he ident ifying cri t eria show n in t a ble 3-7. P ossibleinorga nic soils include lea n cla y (C L), fa t cla y (C H ), silt(ML), a nd ela st ic silt (MH ). The propert ies of a n ela st icsil t a re simila r to t hose for a lea n cla y. H ow ever, the sil tw ill dry q uickly on th e ha nd a nd ha ve a smooth , silky feelw hen dry. S ome soils wh ich cla ssify a s MH a ccording tot he field cla ssifica t ion cri t eria a re difficult to dist ingu ishfrom lean clay s, CL . I t m a y be necessa ry to performla bora t ory t esting t o ensure proper cla ssifica t ion.

Ta ble 3-7.I dent ifica t ion of inorga nic fine-gr a inedsoils from ma nua l tests

Groupsymbol

Dryst rength D ila t a ncy Toughness

ML None t o low S low to

rapid

Low or th read

cannot be formed

C L Medium t o h igh None t o slow Medium

MH Low to medium None t o slow Low t o medium

C H H igh t o very high

None H igh

S ome soils undergo irreversible cha nges upon a ir dr ying.These irreversible processes may cause changes ina t t erberg limits a nd oth er index tests . E ven unsuspectedsoils such as low plasticity si l ts may have differingatterberg l imits due to processes l ike disaggregation.When t ested a t na tur a l moisture , clay par t icles cl ing t o

sil t par t icles result ing in less pla st icity . When dried, t heclay disa ggregat es, ma king a f iner a nd more w ell gra dedmix of pa rt icles w ith increa sed pla st icity.


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For foundation studies of exist ing or new structures,na tur a l moisture a t terberg l imits a re preferred beca useth e in-pla ce ma teria l w ill rema in moist . Na tur a l mois-tur e a t terberg limits a re especial ly import a nt in cr i t ica lstudies, such as earthquake l iquefact ion evaluat ion ofsilt s. On some founda t ion stu dies, such a s for pumpingpla nt d esign, consol ida t ion tests w ill govern, a nd na tur a lmoistur e a t t erbergs a re not required. For borrow st udies,soils will l ikely undergo moisture changes, and naturalmoistur e a t t erberg limits a re not required unless unusua lminera logy is encount ered.

Identification of Organic Fine-Grained Soils. If thesoil cont a ins enough orga nic pa rt icles to influence t he soilpropert ies, cla ssify th e soil as a n or gani c soi l , OL or OH .Orga nic soi ls usua l ly a re da rk brow n t o bla ck a nd usua l lyha ve a n orga nic odor. Often orga nic soils w ill cha ngecolor, (bla ck to brown ) w hen exposed t o a ir. Orga nic soils

norma lly do not ha ve high toughness or pla st icity. Theth read for th e toughness test is spongy. In some ca ses,furt her identifica t ion of orga nic soils a s orga nic sil ts ororga nic cla ys, OL or OH is possible. C orrela t ions betw eenthe d i la tancy, dry s t rength , and toughness tes t s wi thlaboratory tests can be made to classify organic soils ins imi la r ma ter ia l s.

Modifiers for Fine-Grained Soil Classifications. I fba sed on visua l observa t ion, t he soil is est ima t ed to ha ve15 to 25 percent sa nd a nd/or gr a vel, th e words " w ith sa nda nd/or gr a vel" a re a dded t o t he group na me, for exa mple,LE AN C LAY WITH S AND , (C L); S ILT WITH S AND ANDG RAVE L (ML ). Refer t o figur es 3-2 a nd 3-3. I f th e soil isvisua lly est ima t ed t o be 30 percent or more sa nd a nd /orgra vel , the w ords "sa ndy" or " gra vel ly" a re added to thegroup na me. Add the w ord " sa ndy" i f th ere a ppear s to bemore sa nd tha n gra vel . Add the w ord "gra vel ly" i f th ereappears to be more gravel than sand, for example,S AND Y LE AN C LAY (C L); G RAVEL LY F AT C LAY (C H );


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Classify the soil as a CLAYEY GRAVEL (GC) or aC LAYEY S AND (S C ) if t he fines a re cla yey a s determ inedby t he procedures for fine-gra ined soil ident ifica t ion.

Id entify t he soil a s a S IL TY G RAVE L (G M) or a S IL TYS AND (S M) if the fines a re si lt y a s determ ined by th e pro-cedures for fine-gra ined soil ident ifica t ion.

If the soil is visually estimated to contain 10 percentfines, give t he soil a dua l cla ssifica t ion us ing t w o groupsym bols. The first g roup sym bol should corr espond t o aclea n gr a vel or sa nd (G W, G P , SW, SP ), a nd t he secondsym bol should corr espond t o a gra vel or sa nd w ith fines(G C , G M, S C , S M). The typica l na me is the first groupsymbol plus "with clay" or "with si l t" to indicate thepla st icity cha ra ct erist ics of t he fines. For exa mple,WELL GRADED GRAVEL WITH CLAY (GW-GC);P OORLY G RAD E D S AND WITH S IL T (S P -S M). Refer to

figure 3-4.

If t he specimen is predomina nt ly sa nd or gra vel but con-tains an estimated 15 percent or more of the othercoarse-grained const i tuent , the words "with gravel" or" w ith san d" a re a dded to th e group na me. For exam ple:P OORLY G RAD E D G RAVE L WITH S AND (G P ); CL AY-E Y S AND WITH G RAVE L (S C ). Refer t o figur e 3-4.

I f t he field sa mple cont a ined a ny cobbles a nd /or boulders,the words "with cobbles" or "with cobbles and boulders"a re a dded to th e group na me, for exa mple, SI LTY G RA-VE L WITH C OB B LE S (G M).

Abbreviated Soil Classification Symbols

I f spa ce is l imited, a n a bbrevia ted syst em ma y be used t oindica t e the soil cla ssifica t ion sym bol an d na me such a sin logs, da t a ba ses, t a bles, etc. The a bbrevia t ed syst em


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is not a subst i tut e for t he full na me a nd descriptive infor-ma tion but ca n be used in supplementa ry present a t ions.The a bbrevia t ed syst em consist s of th e soil cla ssifica t ionsyst em ba sed on t his cha pter, wit h prefixes a nd suffixesa s l ist ed below .

P refix: s = sa ndy g = gra vellyS uffix: s = w it h sa nd g = w it h gra vel

c = w it h cobbles b = w it h bou ld er s

The soil cla ssifica t ion sym bol is enclosed in pa rent heses.E xamples a re :

C L, sa ndy lea n cla y s(C L)S P -S M, poorly gra ded sa nd (S P -G M)g w i th s il t a nd gra velG P , poor ly gra ded gra vel w it h sa nd, (G P )scb cobbles, a nd boulders

ML, gra velly si lt w ith sa nd g(ML)sc a nd cobbles

Description of the Physical Properties of Soil

Descriptive information for classification and reportingsoil properties such a s a ngula ri ty , sha pe, color, m oistur econdit ions, a nd consist ency a re present ed in t he follow ingparagraphs .

Angularity

Angularity is a descriptor for coarse-grained materialsonly. The a ng ula rit y of t he sa nd (coa rse sizes only),gra vel, cobbles, a nd boulders, a re described a s a ngula r,


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suba ngula r, subrounded, or rounded a s indica ted by t hecri ter ia in ta ble 3-8. A ra nge of a ngula ri ty m a y be sta ted,such a s: sub-round ed t o round ed.

Ta ble 3-8.C rit eria for d escribing a ngu la rit y ofcoa rse-gra ined pa rt icles

Angula r P a r t icles ha ve sha rp edges a nd rela t ivelypla na r sides with unpolished surfa ces.

S u ban g ula r P a r t i cles a r e s im ila r t o an g u la r d es cr ipt ion

but h a ve rounded edges.

S u br ou n ded P a r t i cles h av e n ea r ly plan a r s id es bu t w ell-rounded corners and edges.

R oun ded P a r t icles h a ve sm oot hly cur ved sides a n d n oedges.

Shape

D escribe the sha pe of t he gra vel, cobbles, a nd boulders a sfla t , e longa ted or f la t a nd elonga ted i f th ey meet t hecriteria in ta ble 3-9. In dica t e the fra ct ion of t he pa rt iclest ha t ha ve t he sha pe, such a s: one-t hird of gra vel pa rt icles

a re f la t . I f the ma teria l is to be processed or used a saggregate for concrete , note any unusual ly shapedparticles.

Color

C olor is a n especia lly import a nt propert y in ident ifyingorga nic soils a nd is often import a nt in ident ifying othert ypes of soils. With in a g iven loca lity , color ma y a lso beuseful in identifying m a t eria ls of simila r geologic unit s.C olor sh ould be described for m oist sa mples. Note if color


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Table 3-9.Criteria for describing particle shape

The pa rt icle sha pe is described a s follow s, w here lengt h,w idth, a nd t hickness refer to the great est , intermedia te, an dleas t d imensions of a pa rt icle, respect ively.

F la t P a r t icles w it h w idt h /t h ickness >3.

E longa ted P a r t icles w ith lengt h /w idth >3.

F la t a nd P a r t icles meet cr it er ia for bot h fla t a nd elonga t ed elonga t ed.

represents a dr y condit ion. If the sa mple cont a ins la yersor patches of varying colors, this should be noted, andrepresent a t ive colors sh ould be described. The MunselColor System may be used for consistent colordescriptions.

Odor

D escribe t he odor if orga nic or unu sua l. S oils cont a ininga signif icant amount of organic materia l usual ly havea dist inctive odor of deca ying vegeta t ion. This is espe-cia l ly a ppa rent in fresh sa mples, but i f the sa mples ar e

dried, the odor often ma y be revived by hea t ing a moist -ened sam ple. If the odor is unusua l , such a s tha t of apet roleum product or other chemica l, t he ma t eria l shouldbe described a nd ident ified if known . The ma t erial ma ybe hazardous, and combustion or exposure should beconsidered.

Moisture Conditions

D escribe t he moist ure condit ion a s dry , moist , or w et, a sindica t ed by t he crit eria in t a ble 3-10.


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Ta ble 3-12.C rit eria for describin g consist ency of in -pla ce orund istu rbed fine-gra ined soils

Ver y soft Th u mb w ill pen et r a t e soil mor e t h an 1 in

(25 mm).S oft Thumb w ill penet ra te soil a bout 1 in (25 mm).

F irm Th umb w ill indent soil a bout 1/4 in (5 mm ).

H a rd Thumb w ill not inden t soil but rea dily indent ed wi th thumbnai l .

Very hard Thumbnai l w i ll not inden t soi l.

Cementation

Describe the cementation of intact soils as weak,moderate , or st rong, as indicated by the cr i ter ia int a ble 3-13.

Table 3-13.Criteria for describing cementation

Wea k C rumbles or brea ks w it h ha ndling or lit t lefinger pressure.

Modera te Crumbles or breaks wi th cons iderab le f ingerpressure.

S t ron g Will n ot cr um ble or br ea k w it h fin ger pr essu re.

Structure (Fabric)

Describe the structure of the soil according to criteriadescribed in ta ble 3-14. The descript ors present ed a re forsoils only; t hey a re not syn onym ous w ith descriptors forrock.


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Ta ble 3-15.P a rt icle sizes

Descriptivet erm S ize

Fa miliar example w ithinthe s ize ra nge

B oulder 300 mm or more La rger t ha n a volleyba ll

C obble 300 mm t o 75 mm Volleyba ll - gra pefruit -orange

C oa r se gra vel 75 m m t o 20 m m Ora nge - gra pe

F ine gra vel 20 mm t o No. 4sieve (5 mm)

G ra pe - pea

C oa rse sa nd No. 4 sieve t oNo. 10 sieve

Sidewa lk sa l t

M ed iu m s an d N o. 10 s iev e t oNo. 40 sieve

Openings in window screen

F ine sa nd No. 40 sieve t oNo. 200 sieve

Suga r - ta ble sa l t , grainsbarely visible

D escribe t he ma ximum pa rt icle size found in t he sa mple.For report ing m a ximum pa rt icle size, use the follow ingdescriptors a nd size increment s:

Fine sa nd

Medium san dCoarse sa nd5-mm increment s from 5 mm t o 75 mm25-mm increment s fr om 75 mm t o 300 m m100-m m increm ent s over 300 m m

For example: "m a ximum pa r t i cle s ize 35 mm"

" ma ximum pa rt icle size 400 mm "

If the maximum part ic le size is sand size , describe asfine, medium, or coa rse sa nd; for exa mple, ma ximum pa r-t icle size, medium sa nd.


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If t he ma ximum pa rt icle size is gra vel size, describe thema ximum par t icle size a s t he sma llest s ieve opening t ha tt he pa rt icle w ould pa ss.

If the maximum particle size is cobble or boulder size,describe t he ma ximum dimension of t he lar gest pa rt icle.

Particle Hardness

D escribe th e ha rdness of coa rse sa nd a nd la rger par t iclesa s ha rd , or s ta te wh a t h a ppens w hen t he pa r t icles a re h itby a hammer; e.g. , gravel-size particles fracture withconsiderable hammer blow, some gravel-size particlescrumble w ith ha mmer blow . H a rd mea ns pa rt icles do notfracture or crumble when st ruck with a hammer.Remember tha t the la rger the par t ic le , the harder theblow req uired t o fra ct ur e it . A good pra ct ice is to describethe par t ic le s ize and the method tha t was used to

determine th e ha rdness.

Additional Descriptive Information

Additiona l descriptive inform a t ion m a y include unusua lconditions, geological interpretation or other classifi-ca t ion methods, such a s:

Presence of roots or root holes or other organicma teria l or debris;

D egree of difficult y in d rilling or a ugerin g hole or ex-ca va t ing a pit ; or

Ra veling or ca ving of th e tr ench, h ole, pit , or exposur e;

or

P resence of mica or other predomina nt minera ls.

A loca l or comm ercia l na me a nd /or a geologic int erpret a -t ion should be provided for t he soil.


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A classification or identification of the soil according tooth er classif ica t ion sy stems m a y be a dded.

Narrative Descriptions and Examples

The descript ion sh ould include t he inform a t ion sh ow n intables 3-16 and 3-17, a checklist for the description ofsoils. E xa mple descript ions follow .

Table 3-16.Checklist for the description of soilcla ssifica tion a nd ident ifica tion

1.2.3.4.

5.

6.

7.8.9.

10.

11.

12.

13.14.15.

16.

G roup name a nd symbolP ercent g ra vel, sa nd, a nd/or finesP ercent by volume of cobbles a nd bouldersParticle size

G ra vel - fine, coa rse

S a nd - fine, medium, coa rseP a r t icle angula r i ty angular subangular subrounded roundedP a rt icle sha pe f la t elonga ted f la t a nd elonga tedMa ximum pa rt icle size or dimensionHa rdness of coa rse sand a nd la rger pa rt iclesP la sticity of fines

nonplastic low medium highDry s t rength none low medium high very highDila tancy none slow rapidToughness low medium highC olor (w hen m oist)Odor (if orga nic or un usua l)Moisture dry moist wetReaction w ith HC L none weak s trong


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Ta ble 3-17.C hecklist for t he descriptionof in-place conditions

In -pla ce cond it ions :

1.

2.

3.

4.5.

Consistency (fine-grained soils only) very soft sof t f irm ha rd very ha rdCementat ion weak moderate s trongStructure str a tified la mina ted fissured slickened lensed homogeneousG eologic int erpreta tion a nd/or loca l na me, if a nyAddit iona l comm ents a nd description

P resence of root s or root h olesP resence of mica , gypsum , et c.S urfa ce coa tingsCa ving or sloughing of exca va tionE xca va tion difficulty

E xa mple 1: C LAYEY G RAVE L WITH S AND AND C OB -BLES (GC)Approximately 50 percent fine to coarse,sub-rounded to subangular gravel; approximately30 percent f ine to coarse , subrounded sand;a pproxima t ely 20 per-cent fines w ith medium pla st icity,high dry st rength, no dila t a ncy, medium t oughness; w eakreact ion with HCl; or iginal f ie ld sample had about5 percent (by volume) subr ound ed cobbles, m a ximum size150 mm .

IN-P LACE COND ITIONS : firm, homogeneous, dry ,brown.

G E OLOG IC INTE RP RE TATION: a l luvia l fa n.

Abbrevia t ed sym bol is (G C )sc.

E xa mple 2: WE LL G RAD E D G RAVE L WITH SAND(GW)Approximately 75 percent fine to coarse, hard,sub-angular gravel; approximately 25 percent fine to


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coa rse, ha rd, suba ngula r sa nd; t r a ce of fines; ma ximumsize 75 mm , brow n, dry ; no rea ct ion w ith H Cl.

Abbr evia t ed sym bol is (G W)s

E xa mple 3: S ILTY S AND WITH G RAVE L (S M)Ap-proxima t ely 60 percent predomina nt ly fine sa nd; a pproxi-ma t ely 25 percent si lt y fines wit h low pla st icity, low drystrength, rapid di la tancy, and low toughness; approxi-mately 15 percent fine, hard, subrounded gravel, a few gravel-size part ic les fractured with hammer blow;ma ximum size 25 mm; no rea ct ion w ith H Cl.

IN-P LACE COND ITIONS: f irm, st ra t i f ied, a nd cont a inslenses of silt 1- to 2-in thick, moist, brown to gray;in -pla ce dens it y w a s 106 pound s per cub ic foot (lb/ft 3), a ndin-pla ce moist ure w a s 9 percent .

G E OLOG IC INTE RP RE TATION: ALLU VIU M

Abbrevia t ed sy mbol is (S M)g.

E xa m ple 4: ORG ANI C S OIL (OL/OH )Approxima t ely100 percent fines w ith low pla st icity, slow d ila t a ncy, low dry st rength, and low toughness; wet , dark brown,orga nic odor, w eak r ea ct ion w ith H Cl.

Abbr evia t ed sy mbol is (OL /OH ).

E xa mple 5: S IL TY S AND WITH ORG ANIC FI NE S(S M)Approxima t ely 75 percent fine to coa rse, ha rd , sub-a ngula r r eddish sa nd, a pproxima tely 25 percent orga nicand sil ty dark-brown nonplastic fines with no drystr engt h a nd slow di la ta ncy; wet ; ma ximum size, coa rsesa nd; weak reac t ion w i th H Cl .

Abbrevia t ed sym bol is (S M)


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E xa mple 6: P OORLY G RAD E D G RAVE L WITH S IL T,SAND, COB B LE S, AND B OU LD E RS (G P -G M)Approx-imately 75 percent fine to coarse, hard, subrounded tosuba ngula r gra vel; a pproxima t ely 15 percent fine, ha rd,subrounded to subangular sand; approximately 10 per-cent si l ty nonpla st ic fines; moist , brow n; no rea ct ion w ithHCl; original field sample had approximately 5 percent(by volume) ha rd, subrounded cobbles a nd a t ra ce of ha rd,subrounded boulders with a maximum dimension of500 mm .

Abbrevia t ed sym bol is (G P -G M)scb.

Use of Soil Classification as SecondaryIdentification Method for Materials Other

Than Natural Soils

General

Ma ter ia ls other t ha n na tura l soi ls ma y be class if ied a ndt heir properties ident ified a nd described using t he sa meprocedures present ed in th e preceding subsect ions. Thefollowing materials are not considered soils and shouldnot be given a prima ry U SC S soil classification:

P a rt ia l ly l i thified or poorly cemented m a teria ls

S ha le C la yst oneS a ndst one S ilt st oneD ecomposed gra nite

P rocessed, ma nma de, or oth er ma teria ls

C rushed rock S la gC rushed sa ndst one S hellsC inders Ashes


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Identification cri teria may be used for describing thesematerials, especially for describing particle sizes andsha pes a nd ident i fying th ose ma teria ls wh ich convert t osoils a fter field or la bora t ory processing. D escription for-ma t a nd classif ica t ion for t hese ma teria ls ar e discussedindividua l ly in t he fol low ing par a gra phs.

Partially Lithified or Cemented Materials

P a rt ia l ly li thif ied or poorly cement ed ma teria ls ma y needto be classified because the material will be excavated,processed, or manipulated for use as a constructionma t eria l . When th e physica l propert ies a re t o be deter-mined for t hese ma teria ls for c la ssifica t ion, t he ma teria lmust be processed into a soil by grinding or slaking inw a t er (sha le, si lt st one, poorly indur a t ed a sh deposits).

The physical properties and resulting classification

describe the soil t ype as crea ted by r eworking th e origina lma teria l . S oi l classif ica t ions ca n then be used a s aseconda ry ident ifica t ion. H ow ever, t he cla ssifica t ionsymbol a nd gr oup na me must be report ed in q uota t ionma rks in a ny 1ogs, ta bles, f igures, a nd report s . I flaboratory tests are performed on these materia ls , theresults m ust be report ed a s show n in figure 3-6.

An exa mple of a w ri t t en na rra t ive for e ith er a test pi t ora uger hole log ba sed on visua l cla ssifica t ion is a s follow s:S ym bol D escr ipt ion

Sha le Fragments 3.4- to 7.8-foot (f t ) Sha le Fra gmentsRet rieved a s 2- t o 4-in pieces of sha lefrom power auger hole, dry, brown,

no rea ction w ith HC l. After sla kingin water for 24 hours, materia lcla ssified a s " S AND Y CL AY (C H )"


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Figure 3-6.Sample of test results summary.


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Approxima t ely 60 percent fin es w ithhigh plast ici ty, high dry st rength, nod i l a t a nc y a nd h i gh t oughne ss ;approximately 35 percent fine tomedium, hard sand; approximately5 percent gr a vel-size pieces of sha le.

Processed or Manmade Materials

P rocessed, ma nma de, or oth er ma teria ls ar e a lso used a sconst ruct ion m a teria ls , an d cla ssifica t ion ca n be used a sa seconda ry ident ifica t ion. H ow ever, for t hese processedma teria ls , th e group na me a nd classif ica t ion symbol a reto be w i th in quota t ion mar ks . I f la bora tory tes t s a reperformed on these materia ls , the resul ts must bereport ed a s sh ow n in t a ble 3-6.

An exam ple of a w rit t en na rr a t ive for logs for visua l cla s-

sifica t ion is a s follow s:

S ym bol D escr ipt ion

C RU S H E D R OC K S t ockpile No. 3 C R U S H E DROC K processed gra vel a nd cob-bles fromP.T. NO. 7; "POORLY GRADEDG R AV E L ( G P ) " a p p r o x i m a t e l y90 percent fine, hard, angular,gra vel-size pa rt icles; a pproxima t ely10 percent coarse, angular, sand-size particles; dry, tan, no reactionwi th HC l.

Special Cases for Classification

S ome ma teria ls tha t require a classif ica t ion a nd descrip-t ion a ccord ing t o U S B R 5000 [1] or U S B R 5005 [2] shouldnot have a heading that is a c lassif icat ion group name.


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When t hese ma t eria ls w ill be used in, or influence, designa nd const ruction, t hey sh ould be described a ccording t oth e cr i ter ia for logs of test pits a nd a uger holes a nd t heclassif ica t ion symbol a nd ty pica l na me pla ced in quota -t ion ma rks similar t o the previous d iscussion on second-ary ident i f icat ion method for materia ls other thanna t ura l soils. The hea ding should be a s follow s:

TopsoilLandfi l lRoad sur fa cing U ncompa ct ed or Compa ct edFill

For exa mple:

Classification

S ym bol D escr ipt ion

TOP S O IL 0.0-0.8 m et er (m ) TOP S O IL w ould beclassified as "ORGANIC SILT (OL)."Approxima t ely 80 percent fines w ith low plast ic i ty, s low di la tancy, low drystrength, and low toughness; approxi-mately 20 percent fine to medium sand;w et , da rk brow n, orga nic odor, w eak r ea c-t ion w ith H Cl; roots present th roughout .

S ome ma t erial should be described but not given a cla ssi-fication symbol or group name, such as landfil l ( trash,ga rba ge, etc.) or a spha lt roa d. All of t he a bove l ist edt erms a re only exa mples; this is not a complet e l ist . If t hea bove ma teria ls a re not to be used a nd w ill not inf luencedesign or const ruction, only t he ba sic t erm listed a boveneed be show n on t he logs w ith out a complet e descriptionor classification.


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