Week 6 and 7 - Design and Analysis of Shallow Foundation

8/2/2019 Week 6 and 7 - Design and Analysis of Shallow Foundation

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TOPIC 3: DESIGN AND ANALYSIS OF SHALLOWTOPIC 3: DESIGN AND ANALYSIS OF SHALLOW

FOUNDATIONFOUNDATION

WEEK 6 and WEEK 7WEEK 6 and WEEK 7

SETTLEMENT OF FOUNDATION ON SOILSETTLEMENT OF FOUNDATION ON SOIL

REVIEW OF VERTICAL STRESS DISTRIBUTIONREVIEW OF VERTICAL STRESS DISTRIBUTION

FOUNDATION ON FILLFOUNDATION ON FILL

Learning OutcomesLearning Outcomes

Students should be able to:Students should be able to:

Determine the type of foundation on fill (CO2Determine the type of foundation on fill (CO2--PO10)PO10)

SETTLEMENTSETTLEMENT OF SHALLOW FOUNDATIONOF SHALLOW FOUNDATION

Total settlement = Immediate Settlement + Consolidation Settlement

Immediate settlement (elastic) takes place during or immediately after

the construction of the structure.

Consolidation Settlement occurs over a period of time. Consists of:

Primary squeezing of water from its void

Secondary slippage and reorientation of soil particles

** Refer to ECG433** (Geotechnics II)

Topic Chapter 1:

Stress Distribution in soil and Immediate Settlement

Calculation of Vertical Stress IncreaseCalculation of Vertical Stress Increase

A) Stress Increase due to Concentrated Load

** Refer to ECG433**(Geotechnics II)

Topic Chapter 1:

Stress Distribution in soil

B) Stress due to Circularly Loaded AreaB) Stress due to Circularly Loaded Area Simple Method or Method 2:1Simple Method or Method 2:1

))(( zLzB

Qz

++=

Stress at depth z under

rectangular footing with

dimensions BxL


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))(( zLzB

Qz

++=

Simple Method or Method 2:1Simple Method or Method 2:1OTHER METHODSOTHER METHODS

NewmarksNewmarks ChartChart

FadumsFadums ChartChartPressure Bulbs ChartPressure Bulbs Chart

** Refer to ECG433**(Geotechnics II)

Topic Chapter 1:

Stress Distribution in soil

FOUNDATION ON FILLFOUNDATION ON FILL

Type of FillType of Fill

Non engineered fillNon engineered fill

Engineered fillEngineered fill

Reclaimed landReclaimed land

Foundation SelectionFoundation Selection

May use raft for engineered fillMay use raft for engineered fill need toneed to

confirm before constructionconfirm before construction

Ground improvement for reclaimed landGround improvement for reclaimed land

PVD,PVD, VibroVibro compaction, Dynamiccompaction, Dynamic

ompactionompaction, stone column etc, stone column etc

Piling for non engineered fill.Piling for non engineered fill.

TOPIC 3: DESIGN AND ANALYSIS OF SHALLOWTOPIC 3: DESIGN AND ANALYSIS OF SHALLOW

FOUNDATIONFOUNDATION

WEEK 7WEEK 7

Theoretical and Empirical Method for EstimatingTheoretical and Empirical Method for EstimatingSettlement.Settlement.

Total and Differential Settlement to Limit DamageTotal and Differential Settlement to Limit Damage

Learning OutcomesLearning Outcomes

Students should be able to:Students should be able to:

Able to estimate settlement (CO2Able to estimate settlement (CO2--PO10)PO10)

Able to determine angular distortion (CO2Able to determine angular distortion (CO2--PO10)PO10)

Able to discuss on tolerable settlement. (CO2Able to discuss on tolerable settlement. (CO2--PO10)PO10)


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Elastic SettlementElastic Settlement

Settlement of Rigid Foundation

Empirical Methods


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Method based on Standard Penetration TestElastic Parameters of SoilElastic Parameters of Soil

Correlation

TOTAL SETTLEMENT, ST.

isT SSS ++=(1) Primary consolidationsettlement

(2) Secondary

consolidation settlement

(3) Immediate

settlement

I

EpB

i

21=

p

se

eHS

+

=

1

+=

1

2log1 t

tH

e

CS

p

s

Normally consolidated clays:

++

=0

0

0

log1 p

pp

e

HCS c

He

eS

01+

=

Over-consolidated clays:

If po + p pc.

+

+=

0

0

0

log1 p

pp

e

HCS s

Case 1

If po < pc < po + p

+

++

+=

c

c

o

cs

p

pp

e

HC

p

p

e

HCS 0

00

log1

log1

Case 2

Primary Consolidation Settlement


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Primary Consolidation Settlement Calculations

Secondary Compression Index


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Angular DistortionAngular Distortion

Angular distortion is used to get a limit to prevent theAngular distortion is used to get a limit to prevent the

cracking of structures and architectures finishes an alsocracking of structures and architectures finishes an also

for serviceability of building facilities.for serviceability of building facilities.

A rigid structures would have to limit its angular distortionA rigid structures would have to limit its angular distortion

to less than requirement for a more flexible structures.to less than requirement for a more flexible structures.

Uniform SettlementUniform Settlement Differential SettlementDifferential Settlement

stst2

st1

L

Table 3.1 Apparent Tolerable Differential Settlements

StructureStructure Max Differential SettlementMax Differential Settlement

SingleSingle--storey masonry buildingsstorey masonry buildings 0.0015 L*0.0015 L*

HighHigh masonarymasonary wallwall 0.001 L0.001 L

Continuous steel frameContinuous steel frame 0.002 L0.002 L

Reinforced concrete buildingReinforced concrete building 0.005 L0.005 L

Smokestacks and towersSmokestacks and towers 0.004 L0.004 L

300

112

L

ss tt


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Tolerable Settlement of BuildingsTolerable Settlement of Buildings Guideline for Tolerable SettlementGuideline for Tolerable Settlement

Limiting Angular Distortion

Field Load TestField Load Test

Test in Clay, qu(F) = qu(P)

Sand, qu(F) = qu(P) BF/BP

INTERPRETATION OF IN SITUBEARING CAPACITY

TESTS.

Plate Bearing Test

Estimated immediate settlement of a foundation

(Terzaghi and Peck, 1967) is given by theexpression :

where

sb = settlement of a test plate of side dimension b

sB = settlement of a foundation of side dimension B

at the same intensity of loading.

2

+=

bB

2Bss bB

GEOTECHNIQUES (ECG433) ARM - 2007


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For a given qo

Terzaghi and Peck:

For sand, SF/SP = 4/ (1 +BP/BF)2

Clay, SF = SP. BF/BP

Calculate the average Stress Increase for the clay layer and the

Consolidation Settlement

Example:Example:

Week 6 and 7 - Design and Analysis of Shallow Foundation

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