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Soil Mechanics I

IN304

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Room :228

Phone :0 232 3111585

selim.altun@ege.edu.tr

Office Hours: 9:00am-11:00pm in everyday

Contact Information

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Course Description

This course provides an elementary introduction to

Geotechnical Engineering, and provides the basic

mechanics necessary for the detailed study of

Geotechnical Engineering.This course aims to provide an understanding of: the

nature of soils as engineering materials; common soil

classification schemes; the importance of water in the

soil and the effects of water movement; methods of

predicting soil settlements

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Student Learning Outcomes

By the end of this course students will be able to:

Recognize the physical and engineering properties of soil

Give an engineering classification of any piece of soil, andon this basis predict how it will perform as an engineering

material

Understand the principle of effective stress, and be able toapply this to calculate the stresses causing soil deformation

Calculate quantities of water flowing through the ground,and understand the effects that water flow has on the soil

Calculate the settlements, and rates of settlement, understructures of various shapes and sizes

Explain the advantages and limitations of the differentmethods of settlement calculation

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Lecture Outline

1. Soil Formations (Phase Relationship)

2. Physical Properties

3. Soil Classification

4. Soil Structure (Clay Minerals, etc.)5. Water in Soil (Permeability, Darcy Law, Two

Dimensional Flow, etc)

6. Soil Compaction

7. Stress Distribution in Soil

8. Consolidation and prediction of settlement

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Suggested Textbooks

Craig, R. F. (2004). Soil Mechanics, 7thedition, Taylor &

Francis.

Das, B.M. (1998).Principles of Geotechnical Engineering, 4th

edition, PWS Publishing Company.

Holtz, R.D. and Kovacs, W.D. (1981).An Introduction to

Geotechnical Engineering, Prentice Hall.

Coduto, D.P., (1999). Geotechnical Engineering: Principles and

Practices,Prentice Hall, 1999.

Uzuner, B.A. (2001). zml Problemlerle Zemin Mekanii,

Teknik Yaynevi. (In Turkish)

zaydn, K. (2002).Zemin Mekanii,Birsen Yaynevi. (InTurkish)

(Most of the books have been reserved in the library)

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I.

Soil Formations

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Outline of the First Topic

1. Geotechnical Problems

2. Soil Formations and Deposits

3. Phase Relations

4. Suggested Homework

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1. GEOTECHNICAL PROBLEMS

1.1 Foundations

Prevent the settlementwhich can damage tothe building.

Soil improvement withpre-loading

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1.2. Soils as a construction material

Cross-section of a earthfill dam Cross-section of a highway

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1.3. Slopes and excavations

Underpile and canal excavation

Excavation and revetment systemSlope stability

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1.4. Underground and retaining structure

Retaining wall Buried pipeline

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Solving The Geotechnical Problems

SOIL MECHANICS Stress-strain properties of soil (experimentalstudies)

Theoretical analysis

JEOLOGY, INVESTIGATION

- Litology, soil formationEXPERIENCE

- The results of the earlier applicationsECONOMY

- The applicability of solution routes +Engineering judgement =Solving The Geotechnical Problems

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2. Soil Formations and Deposits

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2.1 Rock Cycles

Soils

(Das, 1998)

The final products

due to weathering are

soils

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2.2 Bowens Reaction Series

The reaction series are similar to the weathering stability series.

More stable

Higher weathering resistance

(Das, 1998)

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Question

What is the main mineral of the sand

particles in general?

Quartz

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2.3 Weathering

2.3.1 Physicalprocesses of weathering Unloading

e.g. uplift, erosion, or change in fluidpressure.

Thermal expansion and contraction

Alternate wetting and drying Crystal growth, including frost action

Organic activity

e.g. the growth of plant roots.

2.3.2 ChemicalProcess of weathering Hydrolysis

is the reaction with waterwill not continue in the static water.involves solubility of silica and alumina

Chelation

Involves the complexing andremoval of metal ions .

Cation exchange

is important to the formation ofclay minerals

Oxidation and reduction.

Carbonationis the combination of carbonate

ions such as the reaction with CO2

2.3.3 Factors affect weathering

Many factors can affect theweathering process such as

climate, topography, features ofparent rocks, biological reactions,and others.

Climatedetermines the amount ofwater and the temperature.

(Mitchell, 1993)

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2.4.2 Transported Soils (Cont.)

(1) Glacial soils: formed by transportation and deposition ofglaciers.

(2) Alluvial soils: transported by running water and depositedalong streams.

(3) Lacustrine soils: formed by deposition in quiet lakes

(4) Marine soils: formed by deposition in the seas.

(5) Aeolian soils: transported and deposited by the wind (e.g.soils in the loess plateau).

(6) Colluvial soils: formed by movement of soil from itsoriginal place by gravity, such as duringlandslide (from Das, 1998)

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3. Phase Relations

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3.1 Three Phases in Soils

S : Solid Soil particleW: Liquid Water (electrolytes)

A: Air Air

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Soil: A 3-Phase Material

Solid

WaterAir

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The Mineral Skeleton

Volume

Solid Particles

Voids (air or

water)

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Three Phase Diagram

Solid

Air

Water

Mineral Skeleton Idealization:

Three Phase Diagram

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Dry Soils

Mineral Skeleton Dry Soil

Air

Solid

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Partly Saturated Soils

Solid

Air

Water

Mineral Skeleton Partly Saturated Soils

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Structural properties (Some concepts)

wn : Natural water content

n : Porozity

e : Void ratio : Bulk density

: Unit weigth (, s, sat, d, )

S : Degree of saturation

G : Specific gravity

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Totalv

olume=V

soil

water

air

Vv

Vs

Vw

Va Mh0

Mw

Ms

Tota

lmass=M

Volume Mass

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3.2 Three Volumetric Ratios

(1) Void ratio e (given in decimal, 0.65)

(2) Porosity n (given in percent 100%, 65%)

(3) Degree of Saturation S (given in percent 100%, 65%)

)V(solidsofVolume

)V(voidsofVolumee

s

v

)V(samplesoilofvolumeTotal

)V(voidsofVolumen

t

v

%100)V(voidsofvolumeTotal

)V(watercontainsvoidsofvolumeTotalS

v

w

e1

e

)e1(V

eVn

s

s

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Volumetric Relationships

Volume Components:

Volume of Solids = Vs

Volume of Water = Vw

Volume of Air = Va Volume of Voids = Va+ Vw= Vv

s

v

V

VeRatioVoid ,

%100(%), T

v

V

VnPorosity

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Volumetric Relationships

Volume Components:

Volume of Solids = Vs

Volume of Water = Vw

Volume of Air = Va Volume of Voids = Va+ Vw= Vv

%100(%), V

w

VVSSaturationofDegree

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3.2.1 Engineering Applications (e)

Typical values Engineering applications:

Volume change tendency

Strength

(Lambe and Whitman, 1979)

Simple cubic (SC), e = 0.91, Contract

Cubic-tetrahedral (CT), e = 0.65, Dilate

Link: the strength of

rock joint

)itan(strengthShear n

i

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3.2.1 Engineering Implications (e)(Cont.)

Hydraulic conductivity

Which packing (SC orCT) has higher hydraulic

conductivity?

SC

e = 0.91

CT

e = 0.65

The fluid (water) can flow more easily through the

soil with higher hydraulic conductivity

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3.2.1 Engineering Applications (e)(Cont.)

SC

e = 0.91

CT

e = 0.65

The finer particle cannot pass

through the voidClogging

Critical state soil mechanics

Filter

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3.2.2 Engineering Applications (S)

Completely dry soil S = 0 %Completely saturated soil S = 100%

Unsaturated soil (partially saturated soil) 0% < S < 100%

Demonstration:

Effects of capillary forces

Engineering implications:

Slope stability

Underground excavation

%100

)V(voidsofvolumeTotal

)V(watercontainsvoidsofvolumeTotalS

v

w

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3.2.2 Engineering Applications (S) (Cont.)

80 % of landslides are due toerosion and loss in suction

The slope stability is significantlyaffected by the surface water.

(Au, 2001)

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3.3 Density and Unit Weight

Mass is a measure of a body'sinertia, or its "quantity ofmatter". Mass is not changed atdifferent places.

Weight is force, the force ofgravity acting on a body. Thevalue is different at various

places (Newton's second law F= ma) (Giancoli, 1998)

The unit weight is frequentlyused than the density is (e.g. incalculating the overburden

pressure).w

s

w

s

w

ss

3

2

g

gG

mkN8.9,Water

secm8.9g

gravitytodueonaccelerati:g

Volume

gMass

Volume

Weight,weightUnit

Volume

Mass,Density

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3.4 Weight Relationships

(1)Water Content w (100%)

For some organic soils w>100%, up to

500 %

For quick clays, w>100%

(2)Density of water (slightly varied

with temperatures)

(3) Density of soila. Dry density

b. Total, Wet, or Moist density (0%

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3.4 Weight Relationships (Cont.)

Submerged unit weight:

Consider the buoyant force

acting on the soil solids:

Archimedes principle:The buoyant force on a body immersed

in a fluid is equal to the weight of the

fluid displaced by that object.

wsat'

wsat

t

wtws

t

wwts

t

wwts

t

wss

V

VWW

V

WVW

%)100S(V

)VV(W

V

VW

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Soil Unit weight (lb/ft3or kN/m3)

Bulk (or Total) Unit weight

= WT/ VT

Dry unit weight

d = Ws/ VT

Buoyant (submerged) unit weight

b = - w

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Typical Unit weights

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3.4.1 Engineering Applications (w)

For fine-grained soils, water playsa critical role to their engineeringproperties (discussed in the next

topic).

For example,

The quick clay usually has a watercontent w greater than100 % and a

card house structure. It will behave

like a viscous fluid after it is fully

disturbed.Clay

particle

Water

(Mitchell, 1993)

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3.5 Other Relationships

(1) Specific gravity

(2)

Proof:

w

s

w

ssG

s

sw

GweS

weS

s

w

w

w

s

s

s

w

w

s

s

ws

s

w

s

v

v

w

s

V

V

V

M

VM

M

M

M

MGw

V

V

V

V

V

VeS

GweS

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3.6 Specific Gravity

Unit weight of Water,w

w = 1.0 g/cm3

(strictly accurate at 4 C) w = 62.4 pcf

w = 9.81 kN/m3

WaterofVolumeEqualanofWeight

ceSubsaofWeightGravitySpecific

tan

WaterofWeightUnitceSubsaofWeightUnitGravitySpecific tan

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Specific Gravity

Iron 7.86

Aluminum 2.55-2.80

Lead 11.34

Mercury 13.55

Granite 2.69

Marble 2.69Quartz 2.60

Feldspar 2.54-2.62

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Typical Values of Specific Gravity

(Lambe and Whitman, 1979)

(Goodman, 1989)

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3.7 Solution of Phase Problems

Remember the following simple rules(Holtz and Kovacs, 1981):

1. Remember the basic definitions of w, e, s, S,

etc.

2. Draw a phase diagram.

3. Assume either Vs=1 or Vt=1, i f not given.

4. Often use wSe=ws, Se = wGs

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Example: Volumetric Ratios

Determine void ratio, porosity and

degree of saturation of a soil core

sample

Data:

Weight of soil sample = 1013g

Vol. of soil sample = 585.0cm3

Specific Gravity, Gs= 2.65

Dry weight of soil = 904.0g

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Solid

Air

Water

Wa~0

Volumes Weights

1013.0g585.0cm3

904.0g

s=2.65

109.0g

341.1cm3

109.0cm3243.9cm

3

134.9cm3

W=1.00

Example

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585.0cm3

Solid

Air

Water

Volumes

s=2.65

341.1cm3

109.0cm3

243.9cm3

134.9cm3

W=1.00

Example

%7.44100

9.243

0.109%100(%)

%7.411000.585

9.243%100(%)

72.01.341

9.243

v

w

T

v

s

v

V

VS

V

Vn

V

V

e

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5. Suggested Homework

1. Please go over example 2-

1 to 2-6 inAn Introduction

to Geotechnical

Engineering, (Holtz, R.D.

and Kovacs, W.D. (1981).Prentice Hall.)

There will be some similar

questions in the final exam.

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6. References

Main References:

Das, B.M. (1998).Principles of Geotechnical Engineering, 4th edition, PWS PublishingCompany. (Chapter 2)

Holtz, R.D. and Kovacs, W.D. (1981).An Introduction to Geotechnical Engineering,Prentice Hall. (Chapter 2)

Others:

Giancoli, D.C. (1998).Physics, 5th edition, Prentice Hall.

Goodman, R.E. (1989).Introduction to Rock Mechanics, 2nd edition, John Wiley & Sons.Head, K. H. (1992).Manual of Soil Laboratory Testing, Volume 1: Soil Classification and

Compaction Test, 2ndedition, John Wiley and Sons.

Lambe, T.W. and Whitman, R.V. (1979). Soil Mechanics, SI Version, John Wiley & Sons.

Mitchell, J.K. (1993).Fundamentals of Soil Behavior, 2nd edition, John Wiley & Sons.