soil compact theory

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Soil Compaction TheorySoil Compaction Theory

Dr. Talat Bader

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CompactionCompaction Soil is used as a basic material for construction

Retaining walls,

Highways, Embankments, Ramps

Airports,

Dams, Dikes, etc.

The advantages of using soil are:

1. Is generally available everywhere2. Is durable - it will last for a long time3. Has a comparatively low cost

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What is Compaction?What is Compaction?

• In most instances in civil engineering and/or construction practice, whenever soils are imported or excavated and re-

applied, they are compacted.• The terms compaction and

consolidation may sound as though they describe the same thing, but in reality they do not.

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What is CompactionWhat is Compaction

• When loose soils are applied to a construction site, compressive mechanical energy is applied to the soil using special equipment to densify the soil (or reduce the void ratio).

• Typically applies to soils that are being applied or re-applied to a site.

Heavy Weight

What do you What do you think about this think about this live compaction live compaction

machinemachine

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What is ConsolidationWhat is Consolidation• When a Static loads are applied to saturated

soils, and over a period of time the increased stresses are transferred to the soil skeleton, leading to a reduction in void ratio.

• Depending on the permeability of the soil and the magnitude of the drainage distance, this can be a very time-consuming process.

• Typically applies to existing, undisturbed soil deposits that has appreciable amount of clay.

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Compaction - Compaction - Consolidation Consolidation

• Compaction means the removal of air-air-filledfilled porosity.

• Consolidation means the removal of water-water-filledfilled porosity.

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Principles of Principles of CompactionCompaction

uncompacted compacted uncompacted compacted

Compaction of soils is achieved by reducing the volume of voids. It is assumed that the compaction process does not decrease the

volume of the solids or soil grains·

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The Goal of CompactionThe Goal of Compaction

• Reduce air-void volume Va in

soils as much as is possible.• For a given water content w,

the max. degree of compaction that can be achieved is when all of the air voids have been removed, that is (S=1).

– Since S = wGs/e, the corresponding void ratio

– (for S=1) will be: e = wGs

Solids

Water

Air

vT

vA

vW

vS

wA

wW

wS

Phase Diagram

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Principles of Principles of CompactionCompaction

The degree of compaction of a soil The degree of compaction of a soil is measured by the is measured by the dry unit weight dry unit weight of the skeleton.of the skeleton.

The dry unit weight The dry unit weight correlatescorrelates with with the degree of packing of the soil the degree of packing of the soil grains. grains.

The more compacted a soil is:The more compacted a soil is:

the smaller its void ratio (e) will be.the smaller its void ratio (e) will be.

Recall that Recall that dd= G= Gssww/(1+e) ·/(1+e) ·Recall that Recall that dd= G= Gssww/(1+e) ·/(1+e) ·

the higher its dry unit weight (the higher its dry unit weight (dd) ) will bewill be

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Typical Calculation (Typical Calculation (dd))• block diagram

shown • Total Mass M = Mw + Ms

• Total Volume V = Vw + Vs

• Void ratio e = Vv / Vs

• Water content w = Mw / Ms

• Saturation S = Vw / Vv

• Moist unit weight

– = (M w + Ms) / V

– = (w + 1) Ms / V = (1+w) d

– d = / (1+w) =

– d = Gsgw/(1+e)

Solids

Water

Air

vT

vA

vW

vS

wA

wW

wS

Phase Diagram

BackBack

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What Does Compaction What Does Compaction Do?Do?1) Increased Shear Strength 1) Increased Shear Strength

This means that larger loads can This means that larger loads can be applied to compacted soils be applied to compacted soils since they are typically stronger.since they are typically stronger.

3) Reduced Compressibility3) Reduced CompressibilityThis also means that larger loads This also means that larger loads

can be applied to compacted soils can be applied to compacted soils since they will produce smaller since they will produce smaller settlements.settlements.

2) Reduced Permeability2) Reduced PermeabilityThis inhibits soils’ ability to absorb This inhibits soils’ ability to absorb

water, and therefore reduces the water, and therefore reduces the tendency to expand/shrink and tendency to expand/shrink and potentially liquefypotentially liquefy

5) Reduce Liquefaction Potential5) Reduce Liquefaction Potential

4) Control Swelling & Shrinking 4) Control Swelling & Shrinking

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Various Types of Various Types of compaction testcompaction test

Type of Type of TestTest MouldMould

HammeHammer mass r mass

(kg)(kg)

Drop Drop (mm)(mm)

No of No of layerslayers

Blows per Blows per layerlayer

BS “Light”BS “Light”One One LiterLiter 2.52.5 300300 33 2727

CBRCBR 2.52.5 300300 33 6262

ASTM (5.5lb)ASTM (5.5lb)4 in4 in 2.492.49 305305 33 2525

6 in6 in 2.492.49 305305 33 5656

BS “Heavy”BS “Heavy”One One LiterLiter 4.54.5 450450 55 2727

CBRCBR 4.54.5 450450 55 6262

ASTM (10lb)ASTM (10lb)4 in4 in 4.544.54 457457 55 2525

6 in 6 in 4.544.54 457457 55 5656

BS Vibration BS Vibration hammerhammer CBRCBR 32 to 4132 to 41 VibrationVibration 33 1 minute1 minute

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General Compaction General Compaction MethodsMethods

Coarse-grained Coarse-grained soilssoils

Fine-grained Fine-grained soilssoils

•Hand-operated vibration platesHand-operated vibration plates

•Motorized vibratory rollersMotorized vibratory rollers

•Rubber-tired equipmentRubber-tired equipment

•Free-falling weight; dynamic Free-falling weight; dynamic compaction (low frequency compaction (low frequency vibration, 4~10 Hz)vibration, 4~10 Hz)

•Falling weight and hammersFalling weight and hammers

•Kneading compactorsKneading compactors

•Static loading and pressStatic loading and press

•Hand-operated Hand-operated tamperstampers

•Sheepsfoot rollers Sheepsfoot rollers

•Rubber-tired rollersRubber-tired rollers

Lab

ora

tor

Lab

ora

tor

yyFie

ldFie

ld

VibrationVibration

•Vibrating hammer (BS)Vibrating hammer (BS)

(Holtz and Kovacs, 1981; Head, 1992)

KneadiKneadingng

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The Standard Proctor The Standard Proctor TestTest

• R.R. Proctor in the early 1930’s was building dams for the old Bureau of Waterworks and Supply in Los Angeles, and he developed the principles of compaction in a series of articles in Engineering News-Record.

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Variables of Variables of CompactionCompaction

Proctor established that compaction is a function of four variables:

• Dry density (d) or dry unit weight d.

• Water content w• Compactive effort (energy E)• Soil type (gradation, presence of clay

minerals, etc.)

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The Standard Proctor The Standard Proctor Test Equipments Test Equipments

Drop Height h=12”

soil Volume 1/30 ft3 or 944 cm3

Diameter 4 in or 10.16 cmHeight 4.584 in or11.643cm

Hammer Weight5.5 lb

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Equipments NeededEquipments NeededFor CompactionFor Compaction

SO-351 Standard Proctor Mold Machined steel, galvanized, 4" i.d., 4.584" height, 2" height of collar

1 Pc

SO-352 Standard Proctor Mold Machined steel, galvanized, 6" i.d., 4.584" height, 2" height of collar

1 Pc

SO-353Standard Proctor Hammer

Machined steel, galvanized, 2" i.d., 12" drop height, 5,5 lbs weight

1 Pc

SO-354Standard Proctor Hammer

Machined steel, galvanized, 2" i.d., 18" drop height, 10 lbs weight

1 Pc

SO-355 Extruder Steel frame, hydraulic jack 1 Set

GE-303 Square Pan Galvanized steel, l 65 x 65 x 7.5 cm 1 Pc

GE-390 Thin Box Alumunium, 60 gr capacity 12 Pcs

GE-405A Graduated Cylinder Plastic, 1.000 ml capacity 1 Pc

GE-801 Scoop Cast Alumunium 1 Pc

GE-871 Trowel Pointed type 1 Pc

GE-890 Straight Edge 30 cm length 1 Pc

GE-900 Rubber Mallet Wooden handle 1 Pc

GE-920 Steel Wiire Brush Wooden handle 1 Pc

ASTM D-698 / D-1557 AASHTO T-99 / T-180For determining moisture - dnesity relationship.

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25 Blows/Layer

Standard Proctor Test Standard Proctor Test o The soil is mixed with varying amounts of

water to achieve different water contents.

Layer or lift # 1

o For each water content,the soil is compacted by dropping a hammer 25 times onto the confined soil

soil

o The soil is in mold will be divided into three liftslifts

Layer or lift # 3

Layer or lift # 2

o Each Lift is compacted 25 timeso This is don 4-6 times from dry-wet

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Standard EnergyStandard Energy

• Compactive (E) applied to soil per unit volume:

mold of Volume

drop) of(height * ight)(hammer we * layers) of (# * r)blows/laye (#E

33

SP /375,12(1/30)ft

ft) (1.0 * lbs) (5.5 * layers) of (3 * ayer)(25blows/lE ftlbft

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Results from Standard Results from Standard Proctor Test Proctor Test

Dry

Den

sit

y (

d)

Water Content (w)

Optimum water content

Maximum dryunit weight

• Optionally, the unconfined compressive strength of the soil is also measured

A sample from the

mold

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Dry Unit Weight Dry Unit Weight

• The compacted soil is removed from the mold and its dry density (or dry unit weight) is measured.

1

md V

Mgm

MV

g

• =Dry Unit weight• =Bulk Density

• =Water Content

• =Total Soil Volume• =Total Wet Soil Mass• =Gravitational Acceleration

Where

d

m

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Water Role in Water Role in Compaction ProcessCompaction Process

Water lubricates the soil grains so Water lubricates the soil grains so that they slide more easily over each that they slide more easily over each other and can thus achieve a more other and can thus achieve a more densely packed arrangement.densely packed arrangement.

– A little bit of water facilitates A little bit of water facilitates compactioncompaction

– too much water inhibits too much water inhibits compactioncompaction. .

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Increase of Density due

to compaction

Den

sit

y (

Mg

/m3)

3

Water content w (%)0 5 10 15 20 25 30 35

2.0

1.9

1.8

1.7

1.6

1.5

1.4

1.3

Density when compactedDry + mass of water added

Increase of density due to mass of water added

Dry Unit Weight

Density when compacted dry

Densi

ty

as Compacted

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Modified Proctor Test Modified Proctor Test

Was developed during World War II By the U.S. Army Corps of

EngineeringFor a better representation of the

compaction required for airfield to support heavy aircraft.

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Modified Proctor Test Modified Proctor Test Same as the Standard Proctor Test

with the following exceptions:

3MP

3MP

/250,56E

(1/30)ft

ft) (1.5 * lbs) (10 * layers) of (5 * ayer)(25blows/lE

ftlbft

soil

The soil is compacted in The soil is compacted in fivefive layers layers

Hammer weight is Hammer weight is 10 Lbs10 Lbs or or 4.54 Kg 4.54 Kg Drop height h is Drop height h is 18 inches18 inches or or 45.72cm45.72cm

# 1

# 3

# 2

# 5

# 4

Then the amount of Then the amount of EnergyEnergy is is calculatedcalculated

3SP /375,12E ftlbft RememberRemember Standard Proctor EnergyStandard Proctor Energy

55.4/375,12

/250,56

E

E3

3

SP

MP

ftlbft

ftlbft

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Effect of Energy on Effect of Energy on CompactionCompaction

EE2 2 > E> E11D

ry D

en

sit

y (

d)

Water Content (w)

Modified E=E2

Standard E=E1

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Comparison-SummaryComparison-SummaryStandard Proctor Standard Proctor

TestTest

• Mold size: 1/30 ft3

• 12 in height of drop• 5.5 lb hammer• 3 layers• 25 blows/layer• Energy 12,375 ft·lb/ft3

Modified Proctor Modified Proctor TestTest

• Mold size: 1/30 ft3

• 18 in height of drop• 10 lb hammer• 5 layers• 25 blows/layer• Energy 56,250 ft·lb/ft3

Dry

Den

sit

y (

Dry

Den

sit

y (

dd))

Water Content (w)Water Content (w)

Modified E=EModified E=E22

Standard E=EStandard E=E11

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Common Compaction Common Compaction Curves Encountered in Curves Encountered in

Practice Practice

Bell-shapedOne & one-half peaks

Double-peaked

Odd-shaped

Water content (w)

Dry

un

it w

eig

ht

d

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2.0

1.9

1.8

1.7

1.60 5 10 15 20 25

Water content w (%)

Dry

d

en

sit

y

( M

g /

m

)3

Line ofLine ofoptimumsoptimums

""ZZerero o AAirir

VVoidoids"s"

ZAV:ZAV:The curve The curve represents the fully represents the fully saturated condition saturated condition (S=100%).(S=100%).

ZAV cannot be reached ZAV cannot be reached by compactionby compaction..

Line of Optimum:Line of Optimum: A A line drawn through the line drawn through the peak points of several peak points of several compaction curves at compaction curves at different compactive different compactive efforts for the same efforts for the same soil will be almost soil will be almost parallel to a 100 % S parallel to a 100 % S curvecurve

Entrapped Air:Entrapped Air: is the is the distance between the distance between the wet side of the wet side of the compaction curve and compaction curve and the line of 100% the line of 100% saturation.saturation.

Zero-Air-VoidZero-Air-Void

Points from the Points from the ZAVZAV curve can curve can be calculated from:be calculated from:

drydry = G = Gssee

Holtz and Kovacs, 1981

Degree of SaturationDegree of SaturationDegree of SaturationDegree of Saturation

StandardProctor

ModifiedProctor

100%100% 60%60% 80%80%

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Wet Wet SidSidee

Dry Dry SidSidee

Results-ExplanationResults-Explanation

Dry

Den

sit

y (

d)

Water Content (w)

OMCOMC

Below wBelow womcomc

Dry of OptimumDry of Optimum•As the water content increases, the particles develop larger and larger water films around them, which tend to “lubricate” the particles and make them easier to be moved about and reoriented into a denser configuration.

Hammer ImpactHammer Impact

•Air expelled from the soil upon impact in quantities larger than the volume of water added.

Below wBelow womcomc

Dry of OptimumDry of Optimum•As the water content increases, the particles develop larger and larger water films around them, which tend to “lubricate” the particles and make them easier to be moved about and reoriented into a denser configuration.

Hammer ImpactHammer Impact

•Air expelled from the soil upon impact in quantities larger than the volume of water added.

At wAt womcomc

The density is at the maximum, and it does

not increase any further.

Above womc

Wet of Wet of OptimumOptimum

Water starts to replace soil particles in the mold, and since w<<s the dry density starts to decrease.Hammer ImpactHammer Impact

Moisture cannot escape under impact of the hammer. Instead, the entrapped air is energized and lifts the soil in the region around the hammer.

Above womc

Wet of Wet of OptimumOptimum

Water starts to replace soil particles in the mold, and since w<<s the dry density starts to decrease.Hammer ImpactHammer Impact

Moisture cannot escape under impact of the hammer. Instead, the entrapped air is energized and lifts the soil in the region around the hammer.

Wet side

Entrappedair

Dry side

Escaping air


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Effects of Soil Types on Effects of Soil Types on CompactionCompaction

Soil texture and Plasticity dataSoil texture and Plasticity data

NONO DescriptionDescription SanSandd

SiltSilt ClaClayy

LLLL PIPI

11Well Well

graded graded loamy sandloamy sand

8888 1010 22 1616 NNPP

22Well Well

graded graded sandy loamsandy loam

7272 1515 1313 1616 NNPP

33Med Med

graded graded sandy loamsandy loam

7373 99 1818 2222 44

44Lean sandy Lean sandy silty claysilty clay 3232 3333 3535 2828 99

55Lean silty Lean silty

clayclay 55 6464 3131 3636 1515

66 Loessial siltLoessial silt 55 8585 1010 2626 22

77 Heavy clayHeavy clay 66 2222 7272 6767 4040

88Poorly Poorly graded graded sandsand

9494 66 66 NPNP NNPP

2.2

2.1

2.0

1.9

1.8

1.7

1.6

5 10 15 20 25

Water content w (%)

Dry

d

en

sit

y (

Mg

/ m

3)

1

2

3

4

5

6

78

Zero air voids, S= 100 Zero air voids, S= 100 %%

The soil type-that is, grain-size distribution, shape of The soil type-that is, grain-size distribution, shape of the soil grains, specific gravity of soil solids, and the soil grains, specific gravity of soil solids, and amount and type of clay minerals presentamount and type of clay minerals present

Holtz and Kovacs, 1981; Das, 1998

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Compaction Compaction CharacteristicsCharacteristics

UUnifiednified SSoiloil CClassificationlassificationGroup Symbol

Compaction

Characteristics

GW

GP

GM

GC

SW

SPSM

SCCL

ML Good to Poor

OL, MH, CH, OH, PT Fair to Poor

Good

Good to Fair

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Embankment MaterialsEmbankment Materials UUnifiednified SSoiloil CClassificationlassification

Group Symbol Value as Embankment Material

GWSW

CL Stable

GP

GM

GCSC

SPSM

ML Poor, gets better with high density

OL, MH, CH, OH, PT Poor, Unstable

Very Stable

Reasonably Stable

Reasonably Stable when Dense

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Subgrade MaterialsSubgrade Materials UUnifiednified SSoiloil CClassificationlassification

Group Symbol Value as Subgrade Material

GW Excellent

GPGM

GCSW

SP

SMSC

MLCL

OL, MH, CH, OH, PT Poor to Not Suitable

Excellent to Good

Good

Good to Fair

Fair to Poor

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Typical Compaction Curve for Cohesionless Sands & Sandy

Gravel

Air dry

Complete saturation

(increasing) Water content

(in

cre

asin

g)

Den

sit

y

bulkingThe low density that is obtained atlow water content is due to capillaryForces resisting arrangements of the sand grains.

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Water & CompactionWater & Compaction

• Increasing the water content at which soil is compacted: Increases the likelihood of

obtaining dispersed soil structure with reduced shear strengths.

Increases the pore pressure in the soil, decreasing the short term shear strength.

Remember what is the Affect

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Structure of Compacted ClayStructure of Compacted ClayD

ry D

en

sit

y

Water Content

High CompactiveEffort

LowCompactive

Effort

Flocculated Structureor

Honeycomb Structureor

Random

Dispersed Structureor

parallel

Intermediatestructure

Lambe and Whitman, 1979

Particle Arrangement Dry side more random

Water DeficiencyDry side more deficient; thus imbibes more water, swells more, has lower pore pressure

Structure

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Effect of Compaction on Effect of Compaction on permeability permeability

Perm

eab

ilit

y

Permeability at constant Permeability at constant compactive effort decreases compactive effort decreases with increasing water content with increasing water content and reaches a minimum at and reaches a minimum at about the optimum.about the optimum.

If compactive effort is If compactive effort is increased, the permeability increased, the permeability decreases because the void decreases because the void ratio decreases.ratio decreases.

Water content

Den

sit

y

From Lambe and Whitman, 1979; Holtz and Kovacs, 1981

Magnitude Dry side more permeable

PermanenceDry side permeability reduced much more by permeation

Permeability

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Pressure, natural scale

Void

ra

tio ,

e

0

Low pressure consolidationPressure, log scale

Void

ra

tio ,

e

0

High-pressure consolidation

Dry compacted orDry compacted or undisturbed sampleundisturbed sample

Compressibility of compacted clays is function of stress level.

Low stress level:Low stress level: Clay compacted wet of optimum are more compressible.

High stress level:High stress level: The opposite is true

Effect of Compressibility

Dry compacted or Dry compacted or undisturbed sampleundisturbed sample

Rebound for both samplesRebound for both samples

From Lambe and Whitman, 1979; Holtz and Kovacs, 1981

Wet compacted or Wet compacted or Remolded sampleRemolded sample

Wet compacted orWet compacted orRemolded sampleRemolded sample

MagnitudeWet side more compressible in low pressure range, dry side in high pressure range

Rate Dry side consolidates more rapidly

Compressibility

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Compressibility & Compressibility & ExpansionExpansion


Compressibility

and Expansion

GW

GP

SW

SP

GM

GC

SM

SC

ML

CL Medium

OL, MH, CH, OH, PT High

Very Little

Slight

Slight to Medium

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Compressibility & Compressibility & ExpansionExpansion


Compressibility and Expansion

GW

GP

GM

GC

SW

SP

SM Slight

SC

ML

CL MediumOL, MH, CH, OH, PT High

Very Little

Slight

Very Little

Slight to Medium

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Effect of Effect of StrengthStrength

From Lambe and Whitman, 1979

Samples Samples (Kaolinite) (Kaolinite) compactecompacted dry of d dry of optimum optimum

tend to be tend to be more rigid more rigid

and and stronger stronger

than than samples samples

compactecompacted wet of d wet of optimumoptimum

200

100

300

400

500

600

0 2 4 6 8 10 12 14 16 18 20Axial Strain (%)

Devia

tion s

tress

(kN

/m2)

20 22 24 26 28 30 32 34 36

135

140

145

150

130

Molding water content (%)

Dry

unit

weig

ht

(kN

/m3)

22 24 26 28 30 32 34 36


Deg

ree o

f P

art

icle

Ori

en

tati

on

20

40

60

100

0

80 ParralParral

RandomRandom

Degree of saturation=

100%

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Unso

ake

d C

BR

(%

)

0

25

50

100

75

Effect of Strength (con)Effect of Strength (con)


The CBR (California bearing ratio)

CBR= resistance required to penetrate a 3-in2 piston into the compacted specimen/ resistance required to penetrate the same depth into a standard sample of crushed stone.

A greater compactive effort produces a greater CBR for the dry of optimum. However, the CBR is actually less for the wet of optimum for the higher compaction energies (overcompaction).25201510

Water content (%)

Dry

densi

ty (

lb/f

t3)

95

100

105

110

120

90

115

55 blows / layer

26 blows / layer

12 blows / layer

06 blows / layer

10

lb h

am

mer

18

“ d

rop (

modifi

ed p

roct

or)

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Comparison of Soil PropertiesComparison of Soil PropertiesDry of Optimum & Wet of Optimum Dry of Optimum & Wet of Optimum

CompactionCompaction

As molded a :Undrained Dry side is much higher b :Drained Dry side is some how higherAfter saturation

a :UndrainedDry side higher if swelling prevented,wet sidecan be hiher if swelling is permitted

b :Drained dry side the same or slpghtly hiherStress-strain modulus Dry side much greaterSensitivity Dry side more apt to be sensitive

Strength

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Wet Wet SidSidee

Dry Dry SidSidee

Effect of SwellingEffect of Swelling

Dry

Den

sit

y (

d)

Water Content (w)

OMCOMC


Higher Higher Swelling Swelling PotentialPotential

Higher Higher Swelling Swelling PotentialPotential

Higher Higher Shrinkage Shrinkage PotentialPotential

Higher Higher Shrinkage Shrinkage PotentialPotential

• Swelling of compacted clays is greater for Swelling of compacted clays is greater for those compacted dry of optimum. those compacted dry of optimum. They They have a relatively greater deficiency of water have a relatively greater deficiency of water and therefore have a greater tendency to and therefore have a greater tendency to adsorb water and thus swell more.adsorb water and thus swell more.

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Compaction and Compaction and ShrinkageShrinkage

• samples samples compacted compacted wet of wet of optimum optimum have the have the highest highest shrinkageshrinkage1.80

1.75

1.70

1.65

1.60

KneadingKneading

VibratoryVibratory

StaticStatic


Dry

d

en

sit

y

( M

g /

m3

)

Wet ofWet ofoptimumoptimum

Dry ofDry ofoptimumoptimum

S = 100%

12 1614 18 20 22 24

OMCOMC

Vibratory compaction

Kneading compaction

Static compaction

LegendLegend

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Engineering PropertiesEngineering PropertiesSummarySummary

Dry side Wet side

Permeability

Compressibility

Swelling

Strength

Structure More random More oriented (parallel)More

permeable

More compressible in high pressure

range

More compressible in

low pressure range

Swell more, higher water

deficiencyHigher

*Shrinkage more

Properties

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SummarySummaryUCS

Group Symbol

Compaction Characteristics

Compressibility and Expansion

Value as Embankment MaterialValue as

Subgrade Material

GW Very Stable Excellent

GP

GM

GC

SW Very Stable

SP

SM Slight

SC Good to Fair Reasonably Stable

ML Good to Poor Poor, gets better with high density

CL Good to Fair Stable

OL, MH, CH, OH, PT

Fair to Poor High Poor, Unstable Poor to Not Suitable

Good

Very Little

Slight

Very Little

Slight to Medium

Reasonably Stable

Reasonably Stable when Dense

Excellent to Good

Good

Good to Fair

Fair to Poor

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Thank youThank you

Question TimeQuestion Time

Dr. Talat BaderDr. Talat Bader

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AppendixAppendix

CE353

Dr.TALAT

BADER

Hand Out 03_2Hand Out 03_2Holtz and Kovacs, 1981

CE353

Dr.TALAT

BADER

Compaction and Earth Compaction and Earth DamDam

• The engineer must consider not only the behavior of the soil as compacted but the behavior of the soil in the completed structure, especially at the time when the stability or deformation of the structure is most critical.

• For example, consider an element of compacted soil in a dam core. As the height of the dam increases, the total stresses on the soil element increase. When the dam is performing its intended function of retaining water, the percent saturation of the compacted soil element is increased by the permeating water. Thus the engineer designing the earth dam must consider not only the strength and compressibility of the soil element as compacted, but also its properties after is has been subjected to increased total stresses and saturated by permeating water.

Lambe and Whitman, 1979Hand Out 03_3

soil compact theory

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