shallow foundation azizi yusoffi 2005 - · pdf filesoils report: 1. site investigation 2. lab...

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FOUNDATION ENGINEERINGFOUNDATION ENGINEERINGBFC 4043BFC 4043

Nor Nor AziziAzizi YusoffYusoffFKAAS, KUiTTHOFKAAS, KUiTTHO

1.0 SHALLOW FOUNDATION

FOUNDATION SYSTEMS

FOUNDATION SYSTEMS

“The foundation is the building element which distributes and transmits

the building load to the earth.”

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Building Load

Soil Bearing CapacitySoil Bearing Capacity

SettlementSettlementSettlementSettlement

ApplicationsApplicationsApplications

LowLowWeightWeight

Soft toSoft toFirm ClayFirm Clay

Large DistributedLarge DistributedWeightWeight

Very Large ConcentratedVery Large ConcentratedWeightWeight

Dense Sand

Strong RockStrong Rock

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“All foundations will settle to some extent”

Settlement Magnitude: Usually less that 1”Uniform Settlement: Acceptable if within the 1”Differential Settlement: Unacceptable if differences

exceed the 1”

Settlement Magnitude: Usually less that 1”Uniform Settlement: Acceptable if within the 1”Differential Settlement: Unacceptable if differences

exceed the 1”

What are the different loads which constitute the building load?

What are the different loads which constitute the building load?

Dead LoadLive Load

Wind Loads Thrusts Seismic

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Seismic

UBC’94 DESIGN BASE SHEAR (V)

= ( Z I C / RW) WZ = Seismic zone factor

I = Importance factor of the building

RW = Reduction factor

S = Site coefficient for soil characteristics

W = Total seismic dead load

T = Fundamental period of vibration

Developing seismic zone

map of Malaysia

Seismic

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Our own seismic zone map

SOIL

GOODGOOD

BADBAD

SOIL TYPES:

Gravel

Sand

Silt

Clay

SOIL TYPES:

Gravel

Sand

Silt

Clay

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How is the bearing capacity of a soil determined ?

1. Building Code provides minimum values that can be used for some structures.

2. Subsurface Exploration • Test Pits (digging a hole) • Test Borings (drilling a hole

with a hollow auger) In either case soil samples are obtained

and tested in a laboratory.

The soil samples are : 1. Classified 2. Properties determined:

• density • moisture content • shear strength • void ratio • bearing capacity • liquid and plastic

limits • plasticity index

The soil samples are : 1. Classified 2. Properties determined:

• density • moisture content • shear strength • void ratio • bearing capacity • liquid and plastic

limits • plasticity index

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GEOTECHNICAL EXPLORATION REPORT VALLEY HOSPITAL

EMERGENCY AND OPERATING ROOM ADDITIONS 629 SHADOW LANE

LAS VEGAS, NEVADA

STEPHENS GEOTECHNICAL INC.

SOILS REPORT:

Geotechnical Investigation or Exploration

SOILS REPORT:

Geotechnical Investigation or Exploration

Soils Report: 1. Site Investigation 2. Lab Investigation 3. Site Conditions 4. Engineering Analysis

and Recommendations • Site Grading &

Earthwork • Foundations & Slabs

on Grade • Lateral Earth

Pressures • Moisture Protection &

Subsurface Drainage • Paving

Soils Report: 1. Site Investigation 2. Lab Investigation 3. Site Conditions 4. Engineering Analysis

and Recommendations • Site Grading &

Earthwork • Foundations & Slabs

on Grade • Lateral Earth

Pressures • Moisture Protection &

Subsurface Drainage • Paving

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CLIMATIC FEATURES

1. Frost line

2. Expansive soil

3. Groundwater

4. Hydrostatic pressure

CLIMATIC FEATURES

1. Frost line

2. Expansive soil

3. Groundwater

4. Hydrostatic pressure

SOME JKR RECOMMENDATIONS

• If the soft layers exist more than 3 meters depth, shallow foundation is not a practical approach, too much digging

• size and types of foundation will depends on the weight (building etc.) and soil bearing capacity

• suitable for soil with SPT more than 5

• Pad footing cannot be build on embankment

• Pad footing is not recommended for cut and fill areas (to handle the differential settlement problem)

• Pad footing is also not suitable at slope areas

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FOUNDATIONS…..FOUNDATIONS…..

ShallowShallow

DeepDeep

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SHALLOW FOUNDATIONS

“Transfer building load at or near soil surface”

SHALLOW FOUNDATIONS

“Transfer building load at or near soil surface”

1. Footings • Column • Strip, Spread • Wall • Combined

2. Slabs • On-grade • Crawlspace • Basement

3. Mat or Raft

1. Footings • Column • Strip, Spread • Wall • Combined

2. Slabs • On-grade • Crawlspace • Basement

3. Mat or Raft

Types of Shallow FoundationTypes of Shallow Foundation

PAD IS CENTERED

UNDER COLUMN

PAD IS CENTERED

UNDER COLUMN

COLUMN FOOTINGCOLUMN FOOTING

FOOTING IS CENTERED

UNDER WALL

FOOTING IS CENTERED

UNDER WALL

WALL FOOTINGWALL FOOTING

COMBINED FOOTINGCOMBINED FOOTING

PROP. LINEPROP. LINE

EXTERIOR COLUMN

EXTERIOR COLUMN

1ST INTERIOR COLUMN1ST INTERIOR COLUMN

CANTILEVER FOOTINGCANTILEVER FOOTING

PROP. LINEPROP. LINE

EXTERIOR COLUMN

EXTERIOR COLUMN

1ST INTERIOR COLUMN

1ST INTERIOR COLUMN

COLUMN FOOTINGSCOLUMN FOOTINGS

CONCRETE BEAM (STRAP)CONCRETE BEAM (STRAP)

SHALLOW FOUNDATIONSSHALLOW FOUNDATIONS

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PLANPLAN SECTIONSECTION

REINFORCING STEEL IN BOTH DIRECTIONS IN BOTTOM FACE OF FOOTING RESISTS TENSIONS CAUSED BY BENDING

REINFORCING STEEL IN BOTH DIRECTIONS IN BOTTOM FACE OF FOOTING RESISTS TENSIONS CAUSED BY BENDING

BENDING OF FOOTING CAUSES COMPRESSION IN TOP FACE AND TENSION IN BOTTOM FACE

BENDING OF FOOTING CAUSES COMPRESSION IN TOP FACE AND TENSION IN BOTTOM FACE

UPWARD SOIL PRESSUREUPWARD SOIL PRESSURE

FOOTINGFOOTING

DOWNWARD COLUMN LOADDOWNWARD COLUMN LOAD

SINGLE COLUMN FOOTINGSINGLE COLUMN FOOTING


SHALLOW FOUNDATIONSSHALLOW FOUNDATIONSFootingsFootings

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Types of Substructures: Slab on-grade

Types of Substructures: Slab on-grade


Types of Substructures: Crawlspace

Types of Substructures: Crawlspace


CRAWLSPACECRAWLSPACE

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KL Tower…..

KL Tower…..

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KL Tower…..

KL Tower…..

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KL Tower…..

KL Tower…..

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BasementBasement

Types of Substructures: Basement






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HYDROSTATIC PRESSURE ON WALLS AND SLABS BELOW

GROUND WATER LINE

HYDROSTATIC PRESSURE ON WALLS AND SLABS BELOW

GROUND WATER LINE

GROUND WATER LINEGROUND WATER LINE

GROUND LINEGROUND LINE




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MAT or RAFTMAT or RAFT

Types of Substructures: Mat or Raft

Types of Substructures: Mat or Raft


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SAFETY FACTOR, What is It???SAFETY FACTOR, What is It???

Soil 1

Soil 2 Stress=Wt./Area

40030010020

FoS=3FoS=3 FoS=1FoS>>3

400

FoS<1

σ

δ

Ultimate

Require more deformation which may not be OK for structures

Allowable

Allow some deformation which may not be problem in long term

Failure

Soil is unable to support load

Safety Factor=Soil capacity/applied load

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SAFETY FACTOR SAFETY FACTOR IN FOUNDATION DESIGNIN FOUNDATION DESIGNTHERE ARE UNCERTAINTIES IN DETERMINING THERE ARE UNCERTAINTIES IN DETERMINING ALLOWABLE STRENGTH DUE TOALLOWABLE STRENGTH DUE TO ::

COMPLEXITY OF SOIL BEHAVIOR COMPLEXITY OF SOIL BEHAVIOR INCOMPLETE KNOWLEDGE OF SUBSURFACE INCOMPLETE KNOWLEDGE OF SUBSURFACE CONDITIONCONDITIONINABILITY TO DEVELOP A GOOD MATH. INABILITY TO DEVELOP A GOOD MATH. MODEL FOR FOUNDATIONS.MODEL FOR FOUNDATIONS.LACK OF CONTROL OF ENVIRONMENTAL LACK OF CONTROL OF ENVIRONMENTAL CHANGE AFTER CONSTRUCTIONCHANGE AFTER CONSTRUCTIONINABILITY TO DETERMINE THE SOIL INABILITY TO DETERMINE THE SOIL PARAMETER ACCURATELYPARAMETER ACCURATELY

VALUE OF SFVALUE OF SF

FAILURE MODE FOUNDATION TYPE FAILURE MODE FOUNDATION TYPE SAFETY FACTORSAFETY FACTOR

SHEAR EARTH WORKS,DAM, FILL 1.2SHEAR EARTH WORKS,DAM, FILL 1.2 -- 1.61.6

SHEAR RET.STRUCTURE SHEAR RET.STRUCTURE 1.5 1.5 -- 2.02.0

SHEAR SHEET PILING COFFERDAM 1.2 SHEAR SHEET PILING COFFERDAM 1.2 -- 1.61.6TEMPORARY BRACED TEMPORARY BRACED EXC.EXC.

SHEAR FOOTINGS: MAT,SPREAD 2 SHEAR FOOTINGS: MAT,SPREAD 2 -- 33

SEEPAGE UPLIFT,HEAVING, SEEPAGE UPLIFT,HEAVING, 1.5 1.5 -- 2.52.5

PIPING PIPING 3 3 -- 55

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Assumption of soil reaction in Assumption of soil reaction in Analyzing shallow foundationAnalyzing shallow foundation

Soil reaction is uniformSoil reaction is uniform

Assumption σ = P/A

Actual

Steps of Shallow Foundation Steps of Shallow Foundation Design ( Footings )Design ( Footings )

1.1. Analyzing load from upper structureAnalyzing load from upper structure2.2. Analyzing soil Conditions, surrounding area, Analyzing soil Conditions, surrounding area,

environment.environment.Obtaining SI Data to Calculate BCObtaining SI Data to Calculate BC

3.3. To Calculate Bearing CapacityTo Calculate Bearing Capacity4.4. To assume a size of foundationTo assume a size of foundation5.5. To Control Stability of SoilTo Control Stability of Soil6.6. To control Settlement and differential To control Settlement and differential

settlementsettlement7.7. Reinforcement Reinforcement

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1.3 Bearing Capacity1.3 Bearing Capacity1.3 Bearing Capacity

Ultimate or serviceability limit state?Ultimate or serviceability limit state?““What is the maximum pressure which the soils can withstand for aWhat is the maximum pressure which the soils can withstand for agiven foundation before the soil will fail?given foundation before the soil will fail?””Design for less but how much less?Design for less but how much less?Uncertainty with respect to:Uncertainty with respect to:

LoadsLoadsCapacityCapacity

Obtaining Ultimate Bearing Obtaining Ultimate Bearing Capacity (Capacity (qquu))

Can be obtained from Soil Investigation; In Can be obtained from Soil Investigation; In situ tests or Laboratory tests.situ tests or Laboratory tests.Lab. TestLab. Test1. 1. TriaxialTriaxial CD, CU, UU, UCTCD, CU, UU, UCT2. Direct Shear Test2. Direct Shear Test3. 3. Lab.VSTLab.VST

..In Situ Test In Situ Test –– SPT,CPT,PMT,VST SPT,CPT,PMT,VST field,Loadingfield,Loading testtest

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Allowable bearing capacity ( Allowable bearing capacity ( qqallall))

qqallall = = qquu / SF/ SF

QQuu = ultimate bearing capacity= ultimate bearing capacity

SF = Safety FactorSF = Safety Factor( 2 ( 2 –– 3 ) for Shallow Foundation3 ) for Shallow Foundation

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Modes of Bearing FailuresModes of Bearing Failures

1.General Shear1.General Shear

2. Local Shear2. Local Shear3. Punch Failure3. Punch Failure

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Terzaghi Bearing Equationfor : - D/B< 1

- Strip Footing

TerzaghiTerzaghi Bearing EquationBearing Equationfor : for : -- D/B< 1D/B< 1

-- Strip FootingStrip Footing

Solution for c and φ only soil

qquu nettnett = = c.Nc.Ncc + q+ q NNqq + 0.5+ 0.5BBγγ'N'Nγγ

Solution for D and φ only soil

Solution for γ and φ only soil

Terzaghi Bearing EquationTerzaghiTerzaghi Bearing EquationBearing Equation

B


qq = = γγ''oo DD

Generalized soil strength : c, Generalized soil strength : c, φφ(drainage as applicable)(drainage as applicable)

Soil unit weight : Soil unit weight : γγ'' (total or(total oreffective as applicable)effective as applicable)

Overburden

Failure Zone (depth ≈ 2B)

Adopt weighted average values !Adopt weighted average values !

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Terzaghi Bearing EquationTerzaghiTerzaghi Bearing EquationBearing Equation

applies to strip footingapplies to strip footingNNcc, , NNqq and and NNγγ are functions of are functions of φφ, and are , and are usually given in graphical form usually given in graphical form c, c, φφ and and γγ' ' refer to soil properties in the refer to soil properties in the failure zone below the footingfailure zone below the footingq q is the effective overburden pressure at is the effective overburden pressure at the founding levelthe founding levelshear strength contribution above footing shear strength contribution above footing level is ignored : conservative for deeper level is ignored : conservative for deeper footings footings


MODIFICATION OF BEARING CAPACITY EQUATIONS FOR WATER TABLE

qquu nettnett = = c.Nc.Ncc + + qq NNqq + 0.5+ 0.5BBγγ''NNγγ

qquu nettnett = = c.Nc.Ncc + q+ q NNqq + 0.5+ 0.5BBγγ''NNγγ


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GENERAL SHEAR FAILURE CASES

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GENERAL SHEAR FAILURE CASES

LOCAL SHEAR FAILURE CASES

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600 N

φ=0 ; C = 35 kN/m2

BEBAN

TANAH

Did u still remember….

QUIZ 1…. 15/7/05

Rajah S1(b) menunjukkan sebuah asas segiempat sama dengan dimensi 1.5m X 1.5m Dengan mempertimbangkan formula Terzaghi dan faktor keselamatan adalah 3, tentukan keupayaan galas yang dibenarkan (allowable bearing capacity capasity) berdasarkan keadaan paras air bumi berikut :(a) Pada permukaan tanah(b) 1.2 m di bawah permukaan

Diberi: qu =1.3 c.Nc + q Nq + 0.4Bγ'Nγ 1200 kN

1.5m x 1.5m

γdry = 11 kN/m3 γsat = 19 kN/m3 φ = 0° c = 22 kN/m2

γdry = 14 kN/m3 γsat = 21 kN/m3 φ = 0° c = 27 kN/m2

1.2 m

qu =1.3 c.Nc + q Nq + 0.4Bγ'Nγ

Chubaaa…

..

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Inclined LoadsInclined LoadsInclined Loads

Correction Factors, Correction Factors, FFcc , , FFqq and and FFγγempirically determined from empirically determined from experimentsexperiments

Fc = Fq = (1 - δ / 90)2

Fγ = (1 - δ / φ)2

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Meyerhof Approx AnalysisMeyerhofMeyerhof Approx AnalysisApprox Analysis

• differs from Terzaghi analysis particularly for buried footings– soil above footing base provides not only

surcharge but also strength– more realistic i.e. less conservative

qquu = = cNcNccssccddcciicc + + qNqNqqssqqddqqiiqq + + 0.50.5γγ'BN'BNγγssγγddγγiiγγ

• s, d, and i are shape, depth and load inclination factors

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qmin

qmax

e

P

e < B/6 :

qmin = P (1-6e/B)/BLqmax = P (1+6e/B)/BL

rigid

Footings with eccentric loadsFootings with eccentric loadsFootings with eccentric loads

qmin = 0qmax = 4P .

3L(B-2e)

qmin

qmax

e

P

e > B/6 : rigid


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Meyerhof Method for eccentric loads

MeyerhofMeyerhof Method for eccentric Method for eccentric loadsloads

PP

ee

L

2e LL' = LL-- 22ee

B

2-way eccentricity22--way eccentricityway eccentricity

PP

ee11

LL

22ee11 LL' = LL-- 22ee11

BB ee2 2

22ee22

BB' =

BB-- 22

ee 22

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Steps of Design: Eccentrically Loaded Foundations

Steps of Design: Eccentrically Steps of Design: Eccentrically Loaded FoundationsLoaded Foundations

1.Define the ‘e’2.Define Qmin and Qmax3.Calculate qult’ using Meyerhof formula

* use B’ and L’ for ‘s’ and ‘i’* use actual B and L for ‘d’

4. Qult = qult’ (B’)(L’)5. FS = Qult / Q

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Analyses by Hansen, VesicAnalyses by Hansen, Analyses by Hansen, VesicVesic

qquu = = cNcNccssccddcciiccggccbbcc + + qNqNqqssqqddqqiiqqggqqbbqq + + 0.50.5γγ'BN'BNγγssγγddγγiiγγggγγbbγγ

Nc ,Nq ,Nγ : Meyerhof bearing capacity factorssc ,sq ,sγ : shape factorsdc ,dq ,dγ : depth factorsic ,iq ,iγ : load inclination factorsgc ,gq ,gγ : ground inclination factorsbc ,bq ,bγ : base inclination factors

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1.4 Assume a size of Foundation1.4 Assume a size of Foundation

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Requirements: Requirements: σσ > 0 , < > 0 , < qqallalle < B/6 , Ae < B/6 , A’’ = a= a-- 2e2eSFSFhorhor < (< (ΣΣV tanV tanδδ + P+ Ppp + C.A)/H+ C.A)/H

It can beIt can be……..Vertical Load onlyVertical Load onlyV + MV + MV + M + HV + M + HV + M + H , Base unsymmetricalV + M + H , Base unsymmetricalCombine footingCombine footing

1.5 Control Stability

SFSFverticalvertical = = qquu / / qqallall

SFSFhorizontalhorizontal = (= (ΣΣV tanV tanδδ + P+ Ppp + C.A) / + C.A) / ΣΣ HH

SFSFSlidingSliding = = ((ΣΣV x Coefficient between base and soil) / V x Coefficient between base and soil) / ΣΣ HH

SFSFOverturningOverturning = = ΣΣ Moment to resist turning / Moment to resist turning / ΣΣ Turning momentTurning moment

☺

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qmin

qmax

e

P

e < B/6 :

qmin = P (1-6e/B)/BLqmax = P (1+6e/B)/BL

rigid


qmin = 0qmax = 4P .

3L(B-2e)

qmin

qmax

e

P

e > B/6 : rigid


50

Meyerhof Method for eccentric loads

MeyerhofMeyerhof Method for eccentric Method for eccentric loadsloads

PP

ee

L

2e LL' = LL-- 22ee

B

2-way eccentricity22--way eccentricityway eccentricity

PP

ee11

LL

22ee11 LL' = LL-- 22ee11

BB ee2 2

22ee22

BB' =

BB-- 22

ee 22

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1.6 Control Settlement & diff. 1.6 Control Settlement & diff. settlementsettlement

Allowable Total SettlementAllowable Total Settlement-- Buildings 15 Buildings 15 -- 50 mm50 mm-- Heavy Industrial bldg. 25 Heavy Industrial bldg. 25 -- 75 mm75 mm-- Bridges 50 mmBridges 50 mmAllowable angular distortionAllowable angular distortion-- Bridges L/125 Bridges L/125 –– L/250L/250-- Buildings L/250 Buildings L/250 –– L/500L/500

Probable additional Moment to upper structureProbable additional Moment to upper structureMM’’ = 6 E I = 6 E I ∆∆ / L/ L22

1.7 ReinforcementOther Subject ( Reinforced concrete design )

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Type of Shallow FoundationType of Shallow Foundation1.1. Rectangular, strip, circular footingRectangular, strip, circular footing2.2. Combined footing; rectangular, trapezoidalCombined footing; rectangular, trapezoidal

cantilevercantilever3.3. Mat / Raft FoundationMat / Raft FoundationThe previous analysis only valid for rigid condition , The previous analysis only valid for rigid condition , λλl < l < ππ/4 /4 For flexible beam condition in which For flexible beam condition in which λλl > l > ππ/4, solution to the analysis should consider/4, solution to the analysis should considerthe flexibility of foundation the flexibility of foundation

3

21

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References…•B.M., Das : Principles of Foundation Engineering

• Liu Evett : Soils and Foundations

• Coduto: Foundation Design

• Dunn, Anderson, Kiefer: Fundamentals of Geotechnical Analysis

•Monash University, Australia

• Ir Mohamed bin Daud, JKR, Kelantan

• Mr Azizul, JKR, Batu Pahat

Thank you for sharing….

Thank youThank you……Nor Nor AziziAzizi YusoffYusoff

[email protected]@kuittho.edu.my013013--76182237618223

shallow foundation azizi yusoffi 2005 - · pdf filesoils report: 1. site investigation 2. lab...

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