Soil Classifications
Transcript of Soil Classifications
-
7/27/2019 Soil Classifications
1/23
Soil Mechanics1CE - 6201
1
Courtesy BS M Nazmul Haqu
Course Teacher
Dr. Md. Mokhlesur Rahma
Professo
Department of Civil Engineerin
DUE
Soil Classification
Soil classification according to their origin and mode
Soil Classify
Inorganic Origin,Inorganic Soil
Organic Origin,Organic Soil
Muck PeatResidual Soil Transported Soil
Black Cotton Soil Lateritics, Coarse Grained
Soil, Have not swellingproperties
Lateritics, Fine Grained Soil,
Have swelling properties
Water Transported Glacier Transported Wind Transported Gravity Transported
Water transported soil
1. Alluvial soil: If soil is deposited by running water.2. Lacustrine soil: If soil is deposited by standing water.3. Marine soil
a. Offshore deposit, takes place in relatively still water below zone of wave action.b. Shore deposit, form from many different shore currents and wave action.
Wind transported soil
1. Aeolian soila. Dunes, in higher proportion, sand deposit.b. Loess, in higher proportion, silt deposit. Saturated loess is collapsible soil.c. Tuff, in higher proportion, ash deposit.
Gravity transported soil
Colluviums soil Talus (Formed by Landslides)
-
7/27/2019 Soil Classifications
2/23
Soil Mechanics1CE - 6201
2
Courtesy BS M Nazmul Haqu
Classification and IndexProperties
(, , , G, n, LL, PL, SL etc)
Classification System("Language")
Engineering Properties
(Permeability, Compressibility,Shrinkage Swell, Shear Strength)
Engineering Purpose
(Highways, Airfields,Foundaiton, Dams etc)
Glacier Transported soil
1. Glacial till, form from melting ice-water depositing soil.2. Moraine, direct deposits of glacier.3. Drift4. Eskers, 10 m to 30 m high and 0.5 to several km long form small tiller.5. Drumlins, 1070 m height and 200800 m long.6. Erraties7. Hardpan, Glacier soil of hard stiffness.8. Varved clay, 3 mm or 1/8 thick or more.
The roles of soil classification system in geotechnical engineering
Systems of soil classification
The Unified Soil Classification System (USCS) The American Association of State Highway and Transportation Officials (AASHTO) Federal Aviation Administration (FAA) Massachusetts Institute of Technology (MIT) or The British Standard Institute (BSI) American Society of Testing and Materials (ASTM)
International System (IS) Unified soil Bureau of Reclamation (USBR)
-
7/27/2019 Soil Classifications
3/23
Soil Mechanics1CE - 6201
3
Courtesy BS M Nazmul Haqu
USCS
75 19 4.75 2.0 0.425 0.075
Gravel Sand
Fines
Silt and Clay
C F C M F
AASHTO
75 2.0 0.425 0.075
Gravel SandSilt and Clay
C F
MIT
2.0 0.6 0.06
Gravel Sand Silt
C F
Clay
0.2
M
0.02 0.006 0.002 0.0006 0.0002
C FM C FCM
IS
0.1 0.05
Glacial Silt Silt
C F
Clay
0.02 0.006 0.002 0.0006 0.0002
C U FM
Sand
2.0
V C
1.0 0.5 0.2
C M F C F
ASTM
0.425
Fine
SandSilt
0.075 0.005
Gravel
2.0
Medium
Sand
0.001
ClayCollodial
Clay
FAA Silt
0.075 0.005
Gravel
2.0
Sand Clay
C - Coarse
M - Medium
F - FineVC - Very Coarse
FC - Fine Collidal
UF - Ultra Fine
FAA - Federal Aviation Administration
USCS - Unified Soil Classification System
AASHTO - American Association of State Highway and Transportation Officials
MIT - Massachusetts Institute of Technology
ASTM - American Society for Testing and MaterialsIS - International Standard
Soil Grain Size in mm
75 4.75 0.075100 0.0002
-
7/27/2019 Soil Classifications
4/23
Soil Mechanics1CE - 6201
4
Courtesy BS M Nazmul Haqu
Four type of common soil
Gravel Sand Silt Clay
Soil classification depending on cohesive properties
Cohesive soilo Gravelo Sando Non Plastic (NP) silt
Cohesive soilo Plastic silto Clay
Uses of soil classification
Foundation design (USCS system)
Highway design (AASHTO system) Airport design (AASHTO system) Agricultural field (USBR system)
Soil tests required for classification
Grain size analysiso Sieve analysiso Hydrometer analysis
Consistency testso Liquid limit testo Plastic limit test
Condition of General Design
Economy Shear failure / shear strength Excess settlement / consolidation properties
Effective Size
This parameter is the diameter in the particle size distribution curve corresponding to l0%
finer. The effective size of a granular soil is a good measure to estimate the hydrauli
conductivity and drainage through soil
Determination of granular or sandy soil whether it is poor or well graded
The co-efficient of uniformity,
The co-efficient of curvature,
-
7/27/2019 Soil Classifications
5/23
Soil Mechanics1CE - 6201
5
Courtesy BS M Nazmul Haqu
0
10%
20%
40%
30%
50%
60%
%FinerbyMass
70%
80%
90%
100%
Grain Size, D (mm)
10 1
10D60D 30D
0.1
Where , and are the diameters corresponding to percents finer than 60, 30, and10% respectively.
For, Gravel when well-graded,
Otherwise Gravel is poor graded.
For, Sand when well-graded,
Otherwise Sand is poor graded.
Plasticity of soil
The plasticity of a soil is its ability to undergo deformation without cracking or fracturing. A
plastic soil can be molded into various shapes when it is wet. Plasticity is an important index
property of fine grained soils, especially clayey soils.
Atterberg limits or Consistency Limits of soil
The moisture contents of a soil at the points where it changes from one state to the other ar
called consistency limits or Atterberg limits.
On the other hand, The moisture content, in percent, at which the soil changes from a liqui
to a plastic state, is defined as the liquid limit (LL). The moisture content, in percent, at which
the soil changes from a plastic to a semisolid state and from a semisolid to a solid state ar
defined as the plastic limit (PL) and the shrinkage limit (SL), respectively. These limits ar
referred to as Atterberg limits.
-
7/27/2019 Soil Classifications
6/23
Soil Mechanics1CE - 6201
6
Courtesy BS M Nazmul Haqu
Atterberg Limits used for
To describe the consistency of fine-grained soils To determines its state or consistency Four states are used to describe the soil consistency; solid, semi-solid, plastic and
liquid
To defining or classifying a soil type or predicting soil performance when used construction material.
Brittle Solid Semi Solid Plastic Solid LiquidState
Water Content,0 SL PL LL
W < PL
W > LLW LL
W PL
Liquidity Index LI < 0 LI = 0 LI > 10 < LI < 1 LI = 1
Stress - StrainDiagram of soil
at various state
Figure: Water content and stress strain graph at various state
Liquid Limit
The increasing moisture content, in percent, at which the soil changes from a plastic to liquistate, is defined as the liquid limit (LL). It offers no shearing resistance and can flow likliquids. The liquid limit of a soil is determined by Casagrandes liquid device (ASTM- D-4318
and is defined as the moisture content at which a groove closure of 12.7 mm or inchoccurs at 25 blows.
Plastic limit
The increasing moisture content, in percent, at which the soil changes from a semisolid tplastic state, is defined as the plastic limit (PL). The soil in the plastic state can be moldedinto various shapes. The Plastic limit of a soil is determined by Casagrandes liquid devic(ASTM- D-4318) and is defined as the moisture content at which the soil crumbles when
rolled into a thread of 3.18 mm in diameter.
Shrinkage limit
The increasing moisture content, in percent, at which the soil changes from a solid to
semisolid state is defined as the shrinkage limit (SL). The shrinkage limit is determined by th
moisture content at which the soil does not undergo any further change in volume with loss omoisture (ASTM - D-427).
Plasticity Index
The difference between the liquid limit and the plastic limit of a soil is defined as the plasticit
index, PI
PI = LLPL.
-
7/27/2019 Soil Classifications
7/23
Soil Mechanics1CE - 6201
7
Courtesy BS M Nazmul Haqu
Liquidity Index
The relative consistency of a cohesive soil in the natural state can be defined by a ratio calle
the liquidity index, which is given by
Where,
Shrinkage Limit Plastic Limit Liquid Limit
Solid Semi-Solid LiquidPlastic
Increasing Moisture
Volume
Drying
The ranges of Liquid limits and Plastic Limits
The range of liquid limit can be from zero to 1000, but most soils have LL less tha100.
The Plastic Limit can range from Zero the 100 or more, with most being less than 40.Determination of Liquid Limit & Plastic Limit
Liquid Limit
The increasing moisture content, in percent, at which the soil changes from a plastic to liquistate, is defined as the liquid limit (LL). It offers no shearing resistance and can flow likliquids. The liquid limit of a soil is determined by Casagrandes liquid device (ASTM- D-4318
and is defined as the moisture content at which a groove closure of 12.7 mm or incoccurs at 25 blows.
The liquid limit (LL) is the water content at which a soil changes from plastic to liquibehavior. The original liquid limit test of Atterberg's involved mixing a pat of clay in a roundbottomed porcelain bowl of 10-12cm diameter. Soil is placed into the metal cup portion of thdevice and a groove is made down its center with a standardized tool of 13.5 millimeter(0.53 in) width. The cup is repeatedly dropped 10mm onto a hard rubber base at a rate of 12blows per minute, during which the groove closes up gradually as a result of the impact. Thnumber of blows for the groove to close is recorded. The moisture content at which it takes 25drops of the cup to cause the groove to close over a distance of 13.5 millimeters (0.53 in) idefined as the liquid limit. The test is normally run at several moisture contents, Liquid limiis determined by plotting a flow curve on a semi -log graph, with no. of blows in log scale anthe water content as ordinate and drawing the best straight line through the plotted points.
-
7/27/2019 Soil Classifications
8/23
Soil Mechanics1CE - 6201
8
Courtesy BS M Nazmul Haqu
Plastic limit
The increasing moisture content, in percent, at which the soil changes from a semisolid tplastic state, is defined as the plastic limit (PL).
The soil in the plastic state can be molded into various shapes. The Plastic limit of a soil idetermined by Casagrandes liquid device (ASTM- D-4318) and is defined as the moistur
content at which the soil crumbles when rolled into a thread of 3.18 mm or in diameter.
soil is considered non-plastic if a thread cannot be rolled out down to 3mm at any moisture.
Hard Rubber Base50 mm
150 mm
Soil 54 mm
22 mm
125 mm
Liquid Limit Apparatus
2 mm
8 mm
20 mm50 mm
20 mm
20 mm
45
10 mm
Casagrande Tool
Divied Soil Cake Before Test Divied Soil Cake After Test
Hard Rubber Base
-
7/27/2019 Soil Classifications
9/23
Soil Mechanics1CE - 6201
9
Courtesy BS M Nazmul Haqu
Liquid Limit
One Point MethodThe determination of liquid limit as explained earlier requires a considerable amount of timand labor. We can use what is termed the 'one-point method' if an approximate value of thlimit is required. The formula used for this purpose is
Where,
Cone Penetrometer method
The soil whose liquid limit is to be determined is mixed well into a soft consistency anpressed into the cylindrical mold of 5 cm diameter and 5 cm high. The cone which has acentral angle of 30 and a total mass including cone, sliding rod and the disk is 80 0.05 gmwill be kept free on the surface of the soil. The depth of penetration 3; of the cone is measurein mm on the graduated scale after 30 sec of penetration. The liquid limit LL ( may bcomputed by using the formula,
( )
30.5 mm
50 mm50 mm
Sliding RodTotal mass = 80 0.5 gm
Cylindrical mold
Calibrated Scale
30
-
7/27/2019 Soil Classifications
10/23
Soil Mechanics1CE - 6201
10
Courtesy BS M Nazmul Haqu
Where,
= The water content corresponding to the penetration y = Liquid Limity = Penetration in mm
Symbols used in the unified soil classification system
Soil Symbol
Gravel G
Sand S
Silt M
Clay C
Organic soil O
Peat Pt
Gradation Symbol
Well graded W
Poorly graded P
Low Plasticity L
High Plasticity H
Plasticity Chart and its Significance
A plasticity chart is used to differentiate the plasticity and organic characteristics of the fine
grained soils based on liquid limit (LL) and plasticity index.
Significance
Used in Unified Soil Classification System Used in AASHTO Soil Classification system Used for Silt-Clay Soil Classification
PlasticityIn
dex(%)
40
30
20
10
0
60
50
10
Liquid Limit (%)
20 30 40 50 60 70 80 90 100
U-Line
Inorganic Silts of Medium
Compressibility and Organic SiltsInorganic Silts of
Low Compressibility
Inorganic Silts of HighCompressibility and Organic
ClaysInorganic Clays
of Low Plasticity
Inorganic Clays of MediumPlasticity
Cohesionless
Soil
Inorganic Clays of High Plasticity
PI=0.9
(LL-
8)
A-L
ine
PI=0.7
3(LL
-20)
CL - ML
CL
ML
orOL
CI CH
MI
orOI
MH
orOH
-
7/27/2019 Soil Classifications
11/23
Soil Mechanics1CE - 6201
11
Courtesy BS M Nazmul Haqu
Field identification procedures for fine grained soil
These procedures are to be performed on the below #40 sieve particles, approximatel0.4 mm.
For field classification purposes, screening is not intended; simply remove by hand thcoarse particles that interfere with the tests.
Dry Strength test
It gives idea crushing characteristics. The part of the soil is completely dried by air drying, sun drying or oven drying. The dry strength is determined by breaking the dried pat and crumbling it betwee
fingers.
The dry strength is a measure of plasticity of the soil. The dry strength depends upon the colloidal fraction of the soil. The strength is termed; high, if the dried pat cannot be powdered at all; medium
considerable pressure is required; and low, if the dry pat can be powdered.
Dilatancy Test
It is the reaction of shaking. A small part of moist soil of about 5 ml in volume is prepared. Water is added to make the soil soft but not sticky. The pat is placed in the open palm of one hand and shaken horizontally striking by th
other hand at bottom of the palm at several times during shaking.
If the soil gives a positive reaction, the water appears on its surface which changes to lively consistency and appears glossy.
When the pat is squeezed between the fingers, the water appears and glossy disappeafrom the surface.
The larger size particles, the quicker is the reaction, called quick if water appears andisappears quickly.
The reaction is termed slow if water appears and disappears slowly. For no reaction, the water does not appear at the surface.
Results
Test ML CL OL MH CH OH MI CI OI
Dilatancy QuickNone to
veryslow
SlowSlow tonone
NoneNone to
VerySlow
Quickto
SlowNone Slow
Toughness None Medium Low High HighLow to
MediumNone Medium Low
DryStrength
Noneof low
Medium SlowLow to
Medium
Highto
VeryHigh
Mediumto High
LowMediumto High
Low toMedium
-
7/27/2019 Soil Classifications
12/23
Soil Mechanics1CE - 6201
12
Courtesy BS M Nazmul Haqu
Toughness test
The pat is rolled on a smooth surface or between the palms into a thread of about mm in diameter.
The thread is folded and re-rolled to reduce the water in soil, due to evaporation bheat of hand, until the 3 mm diameter thread just crumbles.
The water content at that stage is equal to the plastic limit and the resistance tmoulding at that stage is called the toughness.
Dual Symbol and Borderline Classification in USCS.
Soils having between 50% and 12% passing the #200 sieve are classified as Borderline and
have a symbol called dual symbol.
The first part of the dual symbol indicates whether the coarse fraction is well graded opoorly graded. The second part describes the nature of the fines.
For example, a soil classified as a SP-SM means that it is a poorly graded sand witbetween 5% and 12% silty fines.
Similarly, a GW-GC is a well graded gravel with some clayey fines that plot above the Aline.
Fine Grained SoilsCoarse Grained Soils
BorderlineCase
45 50 55
BorderlineCase
0 5 12 100
Percent Passing the #200 Sieve
Gravel
Sand
Silt
ML
GW
GP
SW
SP
Gravel
Sand
GM
GC
SM
SC
MH
OH
Clay
CL
CH
OL
Dual Symbol for 5% to 12% finer particles
Or
GW - GM SW - SM
GW - GC SW - SC
GP - GM SP - SM
GP - GC SP - SC
Dual Symbol for 45% to 55% finer particles
Or
GM - ML SM - ML
GM - MH SM - MH
GC - CL SC - CL
GC - CH SC - CH
-
7/27/2019 Soil Classifications
13/23
Soil Mechanics1CE - 6201
13
Courtesy BS M Nazmul Haqu
The limitations/criticism/drawback of USCS
Although the letter symbols in the USCS are convenient, they do not completeldescribe a soil or soil deposit.
In USCS, do not examine the characteristics as color, odor and homogeneity. In USCS, for coarse-grained soils such items as
o Grain shapeo Mineralogical contento Degree of weatheringo In situ densityo Degree of compaction
are do not express.
Adjectives such as rounded, angular and sub-granular are not used to describe inUSCS.
For the fine grained fraction a) natural water content and b) consistency do not bnoted.
Plasticity Chart for AASHTO Soil Classification System
Plastic
ityIndex(%)
40
30
20
10
0
60
50
10
Liquid Limit (%)
20 30 40 50 60 70 80 90 100
A - 6 and A - 2 - 6
A - 7 - 6
A - 4 and A - 2 - 4 A - 5 and A - 2 - 5
A - 7 - 5 and A - 2 - 7
PI=LL
-30
-
7/27/2019 Soil Classifications
14/23
Soil Mechanics1CE - 6201
14Courtesy
S M Nazmul Ha
Flow Chart of Unified Soil Classification System
Make visual examination of soil to determine whether
it is highly organic, coarse grained, or fine grained. In
borderline cases, determine amount passing through
the #200 sieve
Highly organic soils (Pt)
Fibrous texture, color, odor, very high moisture content,
particles of vegetable matter (sticks, leaves, and so forth)
More than 50% passes the #200 sieve50% or more retained on #200 sieve
Coarse Grained Fine Grained
Run LL and PL on minus
#40 sieve material.
Gravel (G) Sand (S)
Less than 5%
pass #200 sieve
% G > % S % S > % G
Run a Sieve Analysis
Between 5% and
12% pass #200 sieve
More than 12% pass
#200 sieve
Obtain C and C
from grain size graphc u Requires dual symbol
based on gradation and
plasticity characteristics
Run LL and Pl
on minus #40
sieve fraction
Well Graded Poorly Graded
GW GP
GW - GM
GP - GMGW - GCCP - GC
Below "A"
line or
hatched
zone on
plasticity
chart
Limits
plot in
hatched
zone on
plasticity
chart
Above "A"
line and
hatchedzone on
plasticity
chart
GM GM - GC GC
Less than 5%
pass #200 sieveBetween 5% and
12% pass #200 sieve
More than 12% pass
#200 sieve
Obtain C and C
from grain size graphc u
Requires dual symbol
based on gradation and
plasticity characteristics
Run LL and Pl
on minus #40
sieve fraction
Well Graded Poorly Graded
SW SP
SW - SM
SP - SMSW - SCSP - SC
Below "A"
line or
hatchedzone on
plasticity
chart
Limits
plot in
hatchedzone on
plasticity
chart
Above "A"
line and
hatchedzone on
plasticity
chart
SM SM - SC SC
LowLL
HighLL
LL < 50 LL > 50
Below "A"
line or PI 7
Color
or
odor
Organic Inorganic
OL MLML - CL CL
Below "A"
line on
plasticity
chart
Above
line o
plastic
char
Color
or
odor
Organic Inorganic
OH MH CH
Unified Soil Classification System
-
7/27/2019 Soil Classifications
15/23
Soil Mechanics1CE - 6201
15Courtesy
S M Nazmul Ha
Flow Chart of AASHTO Soil Classification
Make visual examination of soil to determine whether
it is highly organic, coarse grained, or fine grained. Inborderline cases, determine amount passing through
the #200 sieve
More than 36% passes the #200 sieve35% or Less passes the #200 sieve
Granular Material
Less than 25%pass #200 sieve
Run a Sieve Analysis
AASHTO Soil Classification System
A - 2
Less than 25%pass #200 sieve
Run sieve analysis, Also
LL and Pl on minus #40sieve material
A - 1
Less than 50%pass #40 sieve
Greater than 51%
pass #40 sieve
Less than 15%
pass #200 sieve,Less than 30%
pass #40 sieve,
Less than 50%pass #10 sieve,
PI less than 6
A - 1 - a
Less than 25%
pass #200 sieve,Less than 50%
pass #40 sieve,
PI less than 6
A - 1 - a
Less than 10%pass #200 sieve,
Non Plastic
A - 3
Run LL and PL on minus#40 sieve material.
SiltyPI < 10
ClayeyPI > 11
LL < 40 LL > 41
A - 2 - 4 A - 2 - 5
LL < 40 LL > 41
A - 2 - 6 A - 2 - 7
Silt-clay Material
Run LL and PL on minus#40 sieve material.
SiltyPI < 10
ClayeyPI > 11
LL < 40 LL > 41
A - 4 A - 5
LL < 40 A - 7LL > 41
A - 6
PI equal to orless than LL
minus 30
A - 7 - 5
PI Greater thaLL minus 30
A - 7 - 6
-
7/27/2019 Soil Classifications
16/23
Soil Mechanics1CE - 6201
16Courtesy B
S M Nazmul Haqu
Plasticity Chart for Classification of Clay Minerals
PlasticityIndex(%)
40
30
20
10
0
50
10
Liquid Limit (%)
20 30 40 50 60 70 80 90 100
U-Line
P
I=0.9(LL
-8)
A-Line
PI=0.73(L
L-20)
MontmorilloniteIllite
Kaolinite
Chlorite
Group Index
The group index is a means of rating the value of a soil as a sub-grade material within its ow
group.
It is a new factor used in the AASHTO soil classification system. It is not used in order to place a soil in a particular group that is done directly from th
results of sieve analysis, the liquid limit and plasticity index.
The higher the value of the group index, the poorer is the quality of the material. The group index is a function of the amount of material passing the # 200 sieve, th
liquid limit and the plasticity index.
Group Index
[ ]
Where,
-
7/27/2019 Soil Classifications
17/23
Soil Mechanics1CE - 6201
17Courtesy B
S M Nazmul Haqu
The value of Group Index should be reported to the nearest whole number but not fraction, say 15.2 15 or 15.6 16.
When the calculated Group Index is negative, shall be reported as 0 (zero). When PI = 0, then particle Group Index formula
[ ] When LL = 0, then particle Group Index formula
[]
The good qualities of a sub-grade material are related as inversely proportional to itGroup index.
For example, a Group Index the value of which is zero, generally indicates a excellensub-grade material.
A Group Index the value of which is 20 indicates a Poor material.Soil Rheology
Soil Rheology is the study of time dependent deformations of soil materials.
For the analysis, the real/physical soil system is placed by an ideal mechanical modecalled the Rheological model, composed of springs, dashpots and friction elements in
various combinations.
The three basic rheological models of practical interest are shown in figureSpring
a) Hookean model
Dashpot
b) Newtonian model c) Yield Stress model
y
These models characterize the stress strain relationship in terms of the materiaconstants known from experiments.
a) Hookean model: Represents a perfect elastic response of soindependent of time, i.e. stress in a linear function of strain, where, K = Spring constant or modulus of elasticity.
b) Newtonian models: Represents a perfect viscous response of soil, i.estress is a linear function of the rate of change in strain with respect t
time,
Where,
c) Yield stress models: the stress can be generate a strain only if Where, is a certain minimum stress necessary for causing strain
or slip.
is yield stress or frictional resistance.
-
7/27/2019 Soil Classifications
18/23
Soil Mechanics1CE - 6201
18Courtesy B
S M Nazmul Haqu
Significance of Liquidity Index, Consistency Index and Toughness Index of Soil
Liquidity Index is defined as
Significances of Liquidity Index
It indicates the nearness of its water content to it, liquid limit.When
LI = 100%, Soil behaves liquid and is at LL
LI = 0%, Soil is at PL
LI = -ve, Soil behaves hard, it indicates a water content < PL.
Consistency Index is defined as
Significances of Consistency Index
Consistency Index shows the nearness of water content of the soil to its Plastic Limit.When
CI = 0%, at LL
CI = 100% at LL = PL
CI > 100% at semisolid state
CI = -ve at water content > LL
LI high then CI low, vice versa.
Toughness Index is defined as
Significances
is a measure of shearing strength of the soil at PL. varies 0 to 3.0. < 1.0 the soil is brittle at het PL.
Flow Index
Flow Index is the slope of the flow curve obtained between the number of blow (abscissa = log
scale) and the water content in Casagrandes method of determination of the liquid limit a
figure.
Significances
is the rate at which a soil mass loses shear strength with an increases in watecontent.
is greater, shear strength lower.
-
7/27/2019 Soil Classifications
19/23
Soil Mechanics1CE - 6201
19Courtesy B
S M Nazmul Haqu
MoistureContent%
40
30
20
10
0
100
90
80
70
60
50
10
No of Blow, N (Log Scale)
N1
W1
W2 (1)
W3
W2 (2)
N2 N3
(1)
(2)
Figure: Flow Index
Activity of soil
The activity (A) of a soil is the ratio between
Plasticity Index and the percent of clay
fraction (F) (less than 2 m) present. The
range of activity of soil is between 1 -2.
When
A1.25 Soil is Active
Significance:
Activity of soil gives information about type
and effect of clay mineral of soil.
0
A(3)
Clay Fraction
Plas
ticityIndex(%)
20
40
60
80
10 20 30 40 50
A(2)
A(1)
Kaolinite
Illite
Montomor illonite
-
7/27/2019 Soil Classifications
20/23
Soil Mechanics1CE - 6201
20Courtesy B
S M Nazmul Haqu
Soil Sensitivity:
Soil sensitivity is the estimate of a soil's ability to maintain its original strength when
bothered or remolded.
The value of sensitivity varies in between 1 to 16.
Where,
Classification of Soils based on Sensitivity
Sensitivity Soil Type
16.0 Quick sensitive
When sensitivity of soil is greater than 8 soil must be treated for construction becaus
disturbance tends to transform them, at least temporarily, into viscous fluids, such a clay
montmorillonite group and posses flocculent structure.
Thixotropy
If a remoulded soil is allowed to stand without further disturbance and changed in wate
content, it may regain at least part of its original strength and stiffness. The increase in
strength of the soil is due to the gradual reorientation of the absorbed molecules of water with
passage of time is called thixotropy.
Engineering use of Consistency Limit
Both Plastic limit and Liquid limit gives the idea upon the type and amount of clay in soil. As grain size decreases, both PL and LL increase.
Plasticity chart plot of PL and LL is extremely useful for classification of fine grainesoils.
LL < 20%, soil is generally sands. Soils with high organic content have low Plasticity Index. Liquid Limit is a indicator of compressibility of a soil. i.e. . Shrinkage Index is a indicator for amount of clay and directly proportional to clay
fraction.
Toughness Index is a measure of shearing strength at PL. When comparing the properties of two soils with equal volume of plasticity Index, it i
found that as the liquid limit increases, the dry strength and toughness decrease
where as compressibility and permeability increases.
-
7/27/2019 Soil Classifications
21/23
Soil Mechanics1CE - 6201
21Courtesy B
S M Nazmul Haqu
When comparing the properties of two soils with equal volume of Liquid limit, it ifound that as the Plasticity Index increases, the dry strength and toughness increase
where as the permeability decreases but compressibility remains almost same.
Particle Size Decrease
PlasticLimit
Plasticity Index
Plastic Limit
Liquid Limit
Silt Clay
-
7/27/2019 Soil Classifications
22/23
Soil Mechanics1CE - 6201
22Courtesy B
S M Nazmul Haqu
Questions
Soil Classification
1. What are the main soil classification depending on origin and mode?2. What are modes of transported soil?3. What is water transported soil?4. Mention wind transported soils?5. Mention glacier transported soils.6. What are the roles of soil classification system in geotechnical engineering?7. What are the systems used of soil classification?8. What are the different soil size limits between USCS and AASHTO systems?9. What are the different soil size limits for ASTM and IS systems?10. Classify soil depending on cohesive property.11. What are engineering field, where soil classification used?12. What are the tests required for types of soil classification?13. On which condition general design on soil depended?14. How will you determine whether a gravel or sandy soil is poor or well graded?15. Define plasticity of soil.16. Define the consistency limits / Atterberg limits.17. Draw the stress - strain diagrams of soil at different limit limits and plastic limits.18. Define plastic limit and liquid limit.19. Define plasticity index and liquidity index.20.What are the ranges of liquid limit and plastic limit?21. Draw neat sketch of Casagrande device.22. State the Casagrande definition for liquid limit determination.23. State the Casagrande definition for plastic limit determination.24.Define one point method for liquid determination.25. State the cone penetrometer method with device for liquid limit determination.26.What are symbols used for unified soil classification?27.Draw plasticity chart.28.For what methods, the plasticity charts are used?29.What are the tests used for field identification of soils?30.State dry strength test of soils in field.31. State dilatancy test of soils in field.32. Compare the results for different field test for organic and inorganic clay and silt.33. Explain the application of A line on plasticity chart for unified classification.34.Explain the application of hatched zone on plasticity chart for unified classification.35. With example define the dual symbol for USCS soil classification.36.Explain the borderline classification in USCS soil classification.37. What are the drawback / limitations / criterion for unified soil classifications?
-
7/27/2019 Soil Classifications
23/23
Soil Mechanics1CE - 6201
23Courtesy B
38.Draw the plasticity chart for AASHTO soil classification system.39. Draw the plasticity chart for classification of clay minerals.40.Define group index with formula.41. Define partial group index formula.42.What are the significances for group index values for practical purposes?43.What are the difference between A 1 a and A 1 b soil?44.
What are the difference between A 2 4, A 2 5, A 2 6 and A 2 7 soils?
45.Define A 3 soil.46.What are the difference between A 4, A 5 and A 6 soils?47.What are the difference between A 7 5 and A 7 6 soils?48.What is meant by Soil Rheology and Rhecological model?49.Define the different rhecological models with figures.50.What are the significances of liquidity index?51. What are the significances of consistency index?52. What are the significances of toughness index?53. Define flow index with significance.54.State activity of soil.55. State sensitivity of soil.56.State thixotrophy of soil.57. What are the engineering uses of Atterbergs limits?58.What are the effects of plasticity index on engineering properties?