Topic3soil Classification1 1212746409556193 9

8/16/2019 Topic3soil Classification1 1212746409556193 9

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III.

Soil Classification


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Outline

1. Purpose

2. Classification Systems

3. The Unified Soil Classification System (USCS)

. !merican !ssociation of State "i#h$ay and

Transportation Officials System (!!S"TO)

%. Su##ested "ome$or&


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1. Purpose

Classifyin# soils into #roups $ith similar 'ehaior in termsof simple indices can proide #eotechnical en#ineers a

#eneral #uidance a'out en#ineerin# properties of the soils

throu#h the accumulated experience.

Simple indices

*S+ ,, PI

Classificationsystem

(,an#ua#e)

-stimateen#ineerin#

properties

!chieeen#ineerin#

purposesUse the

accumulated

experience

Communicate

between

engineers


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2. Classification Systems

Two commonly used systems:

Unified Soil Classification System (USCS).

!merican !ssociation of State "i#h$ay and

Transportation Officials (!!S"TO) System


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3. Unified Soil Classification System

(USCS)Origin of USCS:

This system $as first deeloped 'y Professor !. Casa#rande(1/0) for the purpose of airfield construction durin# orld

ar II. !fter$ards it $as modified 'y Professor Casa#rande

the U.S. ureau of eclamation and the U.S. !rmy Corps of

-n#ineers to ena'le the system to 'e applica'le to dams

foundations and other construction ("olt4 and 5oacs 1/01).

6our ma7or diisions8

(1) Coarse9#rained

(2) 6ine9#rained

(3) Or#anic soils

() Peat


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3.1 +efinition of *rain Si4e

oulders Co''les

*rael Sand Silt and

ClayCoarse 6ine Coarse 6ine;edium

3o.1<

2.< mm

>o.<

o specific

#rain si4e9use

!tter'er# limits


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3.2 *eneral *uidance

Coarse9#rained soils8

*rael Sand

6ine9#rained soils8

Silt Clay

NO.2000.075mm

*rain si4e distri'ution

Cu

Cc

P, ,,

Plasticity chart

50 %

NO. 4

4.75 mm

e?uired tests8 Siee analysis

!tter'er# limit

LL>50

LL


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3.3 Sym'ols

Soil symbols:

*8 *rael

S8 Sand

;8 SiltC8 Clay

O8 Or#anic

Pt8 Peat

i!uid limit symbols:

"8 "i#h ,, (,,@%


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3. Plasticity Chart

("olt4 and 5oacs 1/01)

$%

& The !9line #enerally

separates the more

clayli&e materials

from silty materials

and the or#anics

from the inor#anics. The U9line indicates

the upper 'ound for

#eneral soils.

Note: If the measuredlimits of soils are on

the left of U9line

they should 'e

rechec&ed.


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3.% Procedures for Classification

Coarse9#rained

material

*rain si4e

distri'ution

6ine9#rained

material

,, PI

(Santamarina et al. 2


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3.: -Bample

$#ssing No.200 sie'e (0 )

$#ssing No.4 sie'e 70 )

* ((

$%* +2

$%* 0.7(,-20/ -line

$%*0.7(,((-20*1.41

SC

(≥1% #rael)

Clayey sand $ith#rael

(Santamarina et al. 2


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3.= Or#anic Soils

&igly org#nic soils- $e#t ,"rou3 symbol $T

− ! sample composed primarily of e#eta'le tissue in arious sta#es of

decomposition and has a fi'rous to amorphous teBture a dar&9'ro$n

to 'lac& color and an or#anic odor should 'e desi#nated as a hi#hly

or#anic soil and shall 'e classified as peat PT.

Org#nic cl#y or silt, grou3 symbol O or O&:

− DThe soilEs li?uid limit (,,) after oen dryin# is less than =% of its

li?uid limit 'efore oen dryin#.F If the a'oe statement is true then

the first sym'ol is O.

− The second sym'ol is o'tained 'y locatin# the alues of PI and ,,

(not oen dried) in the plasticity chart.


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3.0 orderline Cases (+ual Sym'ols)

6or the follo$in# three conditions a dual sym'ol should 'eused.

• Coarse9#rained soils $ith % 9 12 fines.− bout 7 ) fines c#n c#nge te ydr#ulic conducti'ity of te co#rse-

gr#ined medi# by orders of m#gnitude.

− The first sym'ol indicates $hether the coarse fraction is $ell or poorly

#raded. The second sym'ol descri'e the contained fines. 6or eBample8 SP9

S; poorly #raded sand $ith silt.

• 6ine9#rained soils $ith limits $ithin the shaded 4one. (PI

'et$een and = and ,, 'et$een a'out 12 and 2%).− It is hard to distin#uish 'et$een the silty and more clayli&e materials.

− C,9;,8 Silty clay SC9S;8 Silty clayed sand.

• Soil contain similar fines and coarse9#rained fractions.− possi'le dual sym'ols *;9;,


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3.0 orderline Cases (Summary)

("olt4 and 5oacs 1/01)


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. !merican !ssociation of State

"i#h$ay and Transportation Officials

system (!!S"TO)Origin of S&TO: ,or ro#d construction

This system $as ori#inally deeloped 'y "o#ento#ler and

Ter4a#hi in 1/2/ as the Pu'lic oads Classification System.

!fter$ards there are seeral reisions. The present !!S"TO(1/=0) system is primarily 'ased on the ersion in 1/%. ("olt4and 5oacs 1/01)


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.1 +efinition of *rain Si4e

oulders *rael Sand Silt9Clay

Coarse 6ine

=% mm No.4

4.75 mm

>o.<

o specific

#rain si4e9use

!tter'er#

limits


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.2 *eneral *uidance

•

0 ma7or #roups8 !1G != ($ith seeral su'#roups) and or#anic soils !0• The re?uired tests are siee analysis and !tter'er# limits.

• The #roup indeB an empirical formula is used to further ealuate soils $ithina #roup (su'#roups).

• The ori#inal purpose of this classification system is used for road construction(su'#rade ratin#).

! G !=!1 G !3

*ranular ;aterials

≤ 3% pass >o. 2o. 2


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.3 *roup IndeB

[ ]

)1


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. Classification

+as 1//0


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. Classification (Cont.)

+as 1//0

>ote8

The first #roup from the left to fit the test data is the

correct !!S"TO classification.


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. -Bample

Passin# >o.2


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%. Su##ested "ome$or&

1. Please read Chapter 3 ("olt4Es oo&).

2. ead !ST; +20= and + 200.

3. Please #o oer -Bample 3.1 and 3.2.


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:. eferences

#in 6eferences:+as .;. (1//0). &rinciples o Geotechnical 'ngineering th edition PS Pu'lishin#

Company. (Chapter 3)

"olt4 .+. and 5oacs .+. (1/01). An (ntroduction to Geotechnical 'ngineering

Prentice "all. (Chapter 3)

Oters:

Santamarina .C. 5lein 5.!. and 6am ;.!. (2

Documents

Topic3soil Classification1 1212746409556193 9