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SOILS AND FOUNDATIONSSOILS AND FOUNDATIONS

Testing

Experience

Theory

Lesson 08Lesson 08Chapter 8 Chapter 8 –– Shallow FoundationsShallow Foundations

TopicsTopics

ggTopic 1 (Section 8.0, 8.1, 8.2, 8.3, 8.4)Topic 1 (Section 8.0, 8.1, 8.2, 8.3, 8.4)-- General and Bearing CapacityGeneral and Bearing Capacity

ggTopic 2 (Section 8.5, 8.6, 8.7, 8.8, 8.9)Topic 2 (Section 8.5, 8.6, 8.7, 8.8, 8.9)-- SettlementSettlement-- Spread footings on embankments, Spread footings on embankments, IGMsIGMs, rocks, rocks-- Effect of deformations on bridge structuresEffect of deformations on bridge structures

ggTopic 3 (Section 8.10)Topic 3 (Section 8.10)-- Construction Construction

Shallow FoundationsShallow Foundations

Lesson 08 Lesson 08 -- Topic 1Topic 1General and Bearing CapacityGeneral and Bearing Capacity

Section 8.0 to 8.4Section 8.0 to 8.4

Learning OutcomesLearning Outcomes

ggAt the end of this session, the participant will At the end of this session, the participant will be able to:be able to:-- Identify different types of shallow foundationsIdentify different types of shallow foundations-- Recall foundation design procedureRecall foundation design procedure-- Contrast factors that influence bearing capacity Contrast factors that influence bearing capacity

in sand and clayin sand and clay-- Compute bearing capacity in sand and clayCompute bearing capacity in sand and clay-- Describe allowable bearing pressure for rock Describe allowable bearing pressure for rock

foundationsfoundations

Stresses Imposed by StructuresStresses Imposed by Structures

ggAbutment and piers may have shallow or deep Abutment and piers may have shallow or deep foundationsfoundations

General Approach to Foundation General Approach to Foundation DesignDesignggDuty of Foundation DesignerDuty of Foundation Designer

-- Establish the most economical design that safely Establish the most economical design that safely conforms to prescribed structural criteria and conforms to prescribed structural criteria and properly accounts for the intended function of properly accounts for the intended function of the structurethe structure

ggRational method of designRational method of design-- Evaluate various foundation typesEvaluate various foundation types

Recommended Foundation Design Recommended Foundation Design ApproachApproachggStep 1:Step 1:

Determine:Determine:-- Direction, type and magnitude of foundation Direction, type and magnitude of foundation

loadsloads-- Tolerable deformationsTolerable deformations-- Special constraintsSpecial constraints

•• UnderclearanceUnderclearance requirementsrequirements•• Structure type, span lengthsStructure type, span lengths•• Time constraints on constructionTime constraints on construction•• Extreme event loadingExtreme event loading•• Construction load requirementsConstruction load requirements


Evaluate subsurface investigation and Evaluate subsurface investigation and laboratory testing data for reliability and laboratory testing data for reliability and completenesscompleteness

Choose design method consistent with Choose design method consistent with quality and quantity of subsurface dataquality and quantity of subsurface data


Consider alternate foundation typesConsider alternate foundation types

Foundation AlternativesFoundation Alternatives

ggShallow FoundationsShallow FoundationsggDeep FoundationsDeep Foundations

-- Piles, shaftsPiles, shafts

Foundation CostFoundation Cost

gg Express foundation capacity in terms of $Express foundation capacity in terms of $

gg TOTAL cost of foundation system divided by the TOTAL cost of foundation system divided by the load supported by the foundation in tonsload supported by the foundation in tons

gg TOTAL cost of a foundation must include ALL TOTAL cost of a foundation must include ALL costs associated with the foundationscosts associated with the foundations-- Need for excavation support system, pile caps, etc.Need for excavation support system, pile caps, etc.-- Environmental restrictionsEnvironmental restrictions-- All other factors as applicableAll other factors as applicable

Foundation CostFoundation Cost

gg If estimated costs of alternative foundation If estimated costs of alternative foundation systems during design are within 15%, the systems during design are within 15%, the alternate foundation designs should be alternate foundation designs should be considered for inclusion in contract considered for inclusion in contract documentsdocuments

Loads and Limit StatesLoads and Limit States

ggLoadsLoads-- Permanent and TransientPermanent and Transient-- Codes specify load combinationsCodes specify load combinations

ggFoundation limit statesFoundation limit states-- Ultimate Ultimate

•• Bearing capacity, eccentricity, sliding, global stability, Bearing capacity, eccentricity, sliding, global stability, structural capacitystructural capacity

-- ServiceabilityServiceability•• Excessive settlement, excessive lateral displacement, Excessive settlement, excessive lateral displacement,

structural deterioration of foundationstructural deterioration of foundation

Types of Shallow FoundationsTypes of Shallow Foundations

gg Isolated Spread FootingsIsolated Spread Footings-- Length (L) to width (B) ratio, L/B < 10Length (L) to width (B) ratio, L/B < 10

Types of Shallow FoundationsTypes of Shallow Foundations

ggCombined Strip Spread FootingsCombined Strip Spread Footings-- Length (L) to width (B) ratio, L/B Length (L) to width (B) ratio, L/B ≥≥ 1010

Shallow Foundations for Bridge Shallow Foundations for Bridge AbutmentsAbutments

Shallow Foundations for Retaining Shallow Foundations for Retaining WallsWalls

Combined FootingsCombined Footings

21

Original Ground

Abutment Fill

Toe of Side Slope

Toe of End Slope

Mat FoundationsMat Foundations

REINFORCED CONCRETE MAT

Spread Footing Design ProcedureSpread Footing Design Procedure

ggGeotechnical design of spread footing is a Geotechnical design of spread footing is a two part processtwo part process

ggFirst Part:First Part:-- Establish an allowable stress to prevent shear Establish an allowable stress to prevent shear

failure in soilfailure in soil

ggSecond Part:Second Part:-- Estimate the settlement under the applied stressEstimate the settlement under the applied stress

Allowable Bearing CapacityAllowable Bearing Capacity

gg Allowable bearing capacity is lesser of:Allowable bearing capacity is lesser of:

Applied stress that will result in shear failure Applied stress that will result in shear failure divided by FSdivided by FS-- Ultimate limit criterionUltimate limit criterion

OROR

Applied stress that results in a specified amount of Applied stress that results in a specified amount of settlement of the structuresettlement of the structure-- Serviceability criterionServiceability criterion

Bearing Capacity ChartBearing Capacity Chart

Effective Footing Width, ft (m)

Allo

wab

le B

earin

g C

apac

ity, k

sf (k

Pa)

Ultimate Bearing Capacity, qult

Contours of Allowable Bearing Capacity for a given settlement

S1 S2 S3

Allowable Bearing Capacity,

FSqq ult

all =

Design Process Flow ChartDesign Process Flow Chart

ggFigure 8Figure 8--1010

Bearing CapacityBearing Capacity

ggBearing capacity failure occurs when the Bearing capacity failure occurs when the shear strength of foundation soil is exceededshear strength of foundation soil is exceeded

ggSimilar to slope stability failureSimilar to slope stability failure

II

I III

DC

A EB

Q

L = ∞ q

ψ

Bearing Bearing Capacity Capacity Failure Failure MechanismsMechanismsggGeneral shearGeneral shearggLocal shearLocal shearggPunching shearPunching shear

(a) GENERAL SHEAR

(b) LOCAL SHEAR

(c) PUNCHING SHEAR

LOAD

SETT

LEM

ENT

LOAD

SETT

LEM

ENT

LOAD

SETT

LEM

ENT

SURFACE TEST

TEST ATGREATERDEPTH

Footing Dimension TerminologyFooting Dimension Terminology

ggBBff = Width of footing= Width of footing-- Least lateral dimensionLeast lateral dimension

ggLLff = Length of footing= Length of footing

ggDDff = Depth of = Depth of embedment of footingembedment of footing

Lf

Df

Bf

Basic Bearing Capacity EquationBasic Bearing Capacity Equation

ggEquation 8Equation 8--88

cc = cohesion= cohesionqq = surcharge at footing base= surcharge at footing baseNNcc, , NNqq, N, Nγγ = Bearing capacity factors= Bearing capacity factorsγγ = unit weight of foundation soil= unit weight of foundation soil

))(Nf)(B( 0.5 )q(N q )c(N c ultq γγ++=

Assumptions of Basic Bearing Assumptions of Basic Bearing Capacity Equation (Section 8.4.3)Capacity Equation (Section 8.4.3)ggStrip (continuous) footingStrip (continuous) footingggRigid footingRigid footingggGeneral shearGeneral shearggConcentric loading (i.e., loading through the Concentric loading (i.e., loading through the

centroidcentroid of the footing)of the footing)ggFooting bearing on level surface of Footing bearing on level surface of

homogeneous soilhomogeneous soilggNo impact of groundwaterNo impact of groundwater

Bearing Capacity FactorsBearing Capacity Factors

1

10

100

1000

0 5 10 15 20 25 30 35 40 45

Friction Angle, degrees

Bea

ring

Cap

acity

Fac

tors

Nq

Nc

Nγ

Figure 8-15Table 8-1

Example 8Example 8--11

γsub = 63 pcf

d = D = 5′ γT = 125 pcf

B = 6′

φ = 20° c = 500 psf


ggSolutionSolution

Effect of Variation of Soil Properties Effect of Variation of Soil Properties and Footing Dimensions (Table 8and Footing Dimensions (Table 8--2)2)

Cohesive Soil

CohesionlessSoil

φ = 0c = 1000 psf

qult (psf)

φ = 30o

c = 0qult (psf)

A. Initial situation: γ = 120 pcf, Df = 0', Bf = 5', deep water table

5140 6720

B. Effect of embedment: Df = 5', γ=120 pcf, Bf = 5', deep water table

C. Effect of width: Bf = 10' γ = 120 pcf, Df = 0', deep water table

D. Effect of water table at surface: γ = 57.6 pcf, Df = 0', Bf = 5'

Properties and Dimensionsγ = γa = effective unit weightγb = submerged unit weightDf = embedment depthBf = footing width (assume strip footing)

Effect of Variation of Soil Properties Effect of Variation of Soil Properties and Footing Dimensions (Table 8and Footing Dimensions (Table 8--2)2)

Cohesive Soil

CohesionlessSoil

φ = 0c = 1000 psf

qult (psf)

φ = 30o

c = 0qult (psf)

A. Initial situation: γ = 120 pcf, Df = 0', Bf = 5', deep water table

5140 6720

B. Effect of embedment: Df = 5', γ=120 pcf, Bf = 5', deep water table

5740 17760

C. Effect of width: Bf = 10' γ = 120 pcf, Df = 0', deep water table

5140 13440

D. Effect of water table at surface: γ = 57.6 pcf, Df = 0', Bf = 5'

5140 3226

Properties and Dimensionsγ = γa = effective unit weightγb = submerged unit weightDf = embedment depthBf = footing width (assume strip footing)

Student Exercise 5Student Exercise 5

ggFind the allowable bearing capacity assuming Find the allowable bearing capacity assuming a FS=3 for the condition shown below for a a FS=3 for the condition shown below for a 10’x50’ footing with rough base10’x50’ footing with rough base

30′

4′

10′

Final Grade

Sandγ = 115 pcfφ = 35°C = 0

Bearing Capacity Correction FactorsBearing Capacity Correction Factors

ggFooting shapeFooting shape-- Adjusted for eccentricityAdjusted for eccentricity

ggDepth of water tableDepth of water tableggEmbedment depthEmbedment depthggSloping ground surfaceSloping ground surfacegg Inclined baseInclined basegg Inclined loadingInclined loading


ggSolutionSolution

Modified Bearing Capacity EquationModified Bearing Capacity EquationEquationEquation 88--1111

gg sscc, s, sγγ, s, sqq shape correction factorsshape correction factors

gg bbcc, b, bγγ, , bbqq base inclination correction factorsbase inclination correction factors

gg CCwqwq, , CCwwγγ groundwater correction factorsgroundwater correction factors

gg ddqq embedment correction factorembedment correction factor

gg NNcc, N, Nγγ, , NNqq bearing capacity factors as function of bearing capacity factors as function of φφ

γγγγγ++= bsCNB5.0dbsCqN bscNq WfqqqqWqcccult

Estimation of Estimation of φφ for Bearing Capacity for Bearing Capacity Factors (Table 8Factors (Table 8--3)3)

Description VeryLoose Loose Medium Dense Very

Dense

Corrected N-value N160

0 4 10 30 50

Friction angleφ Degrees

25 –30

27 –32 30 – 35 35 –

4038 –

43

Moist unit weight (γ) pcf

70 –100

90 –115

110 –130

120 –140

130 –150

Shape Correction FactorsShape Correction Factors

ggBasic equation assumes strip footing which Basic equation assumes strip footing which means means LLff/B/Bff ≥≥ 1010

ggFor footings with For footings with LLff/B/Bff << 1010 apply shape apply shape correction factorscorrection factors

ggCompute the effective shape of the footing Compute the effective shape of the footing based on eccentricitybased on eccentricity

Effective Footing DimensionsEffective Footing Dimensions

B′f = Bf – 2eB ; L′f = Lf – 2eL ; A′= B′f L′f

Pressure DistributionsPressure Distributions

Structural designStructural design Sizing the footingSizing the footing

Shape Correction FactorsShape Correction Factors

FactorFriction Angle

Cohesion Term (sc)

Unit Weight

Term (sγ)

Surcharge Term (sq)

φ = 0 1.0 1.0

φ > 0

Shape Factors,sc, sγ, sq ⎟⎟

⎠

⎞⎜⎜⎝

⎛φ+ tan

LB1

f

f

⎟⎟⎠

⎞⎜⎜⎝

⎛+

f

fL5B1

⎟⎟⎠

⎞⎜⎜⎝

⎛⎟⎟⎠

⎞⎜⎜⎝

⎛+

c

q

f

fNN

LB1 ⎟⎟

⎠

⎞⎜⎜⎝

⎛−

f

fLB4.01

gg In routine foundation design, use of effective In routine foundation design, use of effective dimensions in shape factors is not practicaldimensions in shape factors is not practical

Location of Groundwater tableLocation of Groundwater table

ggTo correct the unit weightTo correct the unit weight

DW CWγ CWq0 0.5 0.5Df 0.5 1.0

> 1.5Bf + Df 1.0 1.0Note: For intermediate positions of the groundwater table, interpolate between the values shown above.

Embedment DepthEmbedment DepthggTo account for the To account for the

shearing resistance in shearing resistance in the soil above the the soil above the footing basefooting base

Friction Angle, φ(degrees) Df/Bf dq

32

1248

1.201.301.351.40

37

1248

1.201.251.301.35

42

1248

1.151.201.251.30

See Note

Note: The depth correction factor should be used only when the soils above the footing bearing elevation are as competent as the soils beneath the footing level; otherwise, the depth correction factor should be taken as 1.0.

Sloping Ground SurfaceSloping Ground Surface

ggModify the bearing capacity equation as Modify the bearing capacity equation as follows:follows:

ggUseful in designing footings constructed Useful in designing footings constructed within bridge approach fillswithin bridge approach fills

))(N)(B( 0.5 )(N c q qfcqult γγ+=

Footing in SlopeFooting in Slope

Footing Near SlopeFooting Near Slope

Inclined BaseInclined BaseggFootings with inclined base should be Footings with inclined base should be

avoided or avoided or limtedlimted to angles less than 8to angles less than 8--1010ººggSliding may be an issue for inclined basesSliding may be an issue for inclined bases

⎟⎠⎞

⎜⎝⎛ α

−3.147

1⎟⎟⎠

⎞⎜⎜⎝

⎛

φ

−−

tanNb1

bc

qq

Cohesion Term (c)

Unit Weight Term (γ)

Surcharge Term (q)

bc bγ bq

φ = 0 1.0 1.0

φ > 0 (1-0.017α tanφ)2 (1-0.017α tanφ)2

φ= friction angle, degrees; α = footing inclination from horizontal, upward +, degrees

Base Inclination Factors,bc, bγ, bq

FactorFriction Angle

Inclined LoadingInclined Loading

gg If shear (horizontal) component is checked If shear (horizontal) component is checked for sliding resistance, the inclination for sliding resistance, the inclination correction factor is omittedcorrection factor is omitted

ggUse effective footing dimensions in Use effective footing dimensions in evaluation of the vertical component of the evaluation of the vertical component of the loadload

Comments on Use of Bearing Comments on Use of Bearing Capacity Correction FactorsCapacity Correction FactorsggFor settlementFor settlement--controlled allowable bearing controlled allowable bearing

capacity, the effect application of correction capacity, the effect application of correction factors may be negligiblefactors may be negligible

ggApplication of correction factors is Application of correction factors is secondary to the adequate assessment of secondary to the adequate assessment of the shear strength characteristics of the the shear strength characteristics of the foundation soil through correctly performed foundation soil through correctly performed subsurface explorationsubsurface exploration

Local or Punching ShearLocal or Punching Shear

c* = 0.67cc* = 0.67cφφ*=tan*=tan--11(0.67tan(0.67tanφφ))

ggLoose sandsLoose sandsggSensitive claysSensitive claysggCollapsible Collapsible

soilssoilsggBrittle claysBrittle clays

Bearing Capacity Factors of SafetyBearing Capacity Factors of Safety

ggqqallall = allowable bearing capacity= allowable bearing capacityggqqultult = ultimate bearing capacity= ultimate bearing capacityggTypical FS = 2.5 to 3.5Typical FS = 2.5 to 3.5ggFS is a function ofFS is a function of

-- Confidence in shear strength parameter, c and Confidence in shear strength parameter, c and φφ-- Importance of structureImportance of structure-- Consequences of failureConsequences of failure

FSq

q ultall =

Overstress AllowancesOverstress Allowances

ggFor shortFor short--duration infrequently duration infrequently occuringoccuringloads, an overstress of 25 to 50 % may be loads, an overstress of 25 to 50 % may be allowed for allowable bearing capacityallowed for allowable bearing capacity

Practical Aspects of Bearing Practical Aspects of Bearing CapacityCapacity

Presumptive Allowable Bearing Presumptive Allowable Bearing CapacityCapacityggNOT recommended for soilsNOT recommended for soilsggSee Tables 8See Tables 8--8, 88, 8--9 and 89 and 8--10 for rocks10 for rocks


ggAt the end of this session, the participant will At the end of this session, the participant will be able to:be able to:-- Identify different types of shallow foundationsIdentify different types of shallow foundations-- Recall foundation design procedureRecall foundation design procedure-- Contrast factors that influence bearing capacity Contrast factors that influence bearing capacity

in sand and clayin sand and clay-- Compute bearing capacity in sand and clayCompute bearing capacity in sand and clay-- Describe allowable bearing pressure for rock Describe allowable bearing pressure for rock

foundationsfoundations

Any Questions?Any Questions?

THE ROAD TOUNDERSTANDING

SOILSAND

FOUNDATIONS


Lesson 08 Lesson 08 -- Topic 2Topic 2Settlement, footings on embankments, Settlement, footings on embankments, IGMsIGMs, ,

rocks, effect of deformations on bridge structuresrocks, effect of deformations on bridge structuresSection 8.5 to 8.9Section 8.5 to 8.9


ggAt the end of this session, the participant will At the end of this session, the participant will be able to:be able to:-- Calculate immediate settlements in granular Calculate immediate settlements in granular

soilssoils-- Calculate consolidation settlements in saturated Calculate consolidation settlements in saturated

finefine--grained soilsgrained soils-- Describe tolerances and consequences of Describe tolerances and consequences of

deformations on bridge structuresdeformations on bridge structures

Settlement of Spread FootingsSettlement of Spread Footings

gg Immediate (shortImmediate (short--term)term)ggConsolidation (longConsolidation (long--term)term)

Immediate SettlementImmediate Settlement

ggHough’s methodHough’s method-- Conservative by a factor of 2 (FHWA, 1987)Conservative by a factor of 2 (FHWA, 1987)

ggSchmertmann’sSchmertmann’s methodmethod-- More rationalMore rational-- Based on nonlinear theory of elasticity and Based on nonlinear theory of elasticity and

measurementsmeasurements

ChartsChartsFigure 2Figure 2--1111ggDDss = 4B to 6B = 4B to 6B

for continuous for continuous footings where footings where LLff/B/Bff ≥≥ 1010

ggDDss = 1.5B to 2B = 1.5B to 2B for square for square footings where footings where LLff/B/Bff == 11

Trend of Analytical Trend of Analytical Results and Results and MeasurementsMeasurements

Legend:Legend:

Square footings Square footings where where LLff/B/Bff =1=1

Continuous footings Continuous footings where where LLff/B/Bff ≥≥ 1010

Vertical Strain, %

Dep

th b

elow

Foo

ting

2B

4B

SchmertmannSchmertmann MethodMethod

gg IIzz Strain Influence FactorStrain Influence Factorgg EE Elastic Modulus, Table 5Elastic Modulus, Table 5--2020gg XX Modification factor for EModification factor for Egg CC11 Correction factor for strain reliefCorrection factor for strain reliefgg CC22 Correction factor for creep deformationCorrection factor for creep deformation

∑=

ΔΔ=n

1ii21i HpCCS ⎟

⎠⎞

⎜⎝⎛=Δ

XEI

HH zci

5.0p

p5.01C o

1 ≥⎟⎟⎠

⎞⎜⎜⎝

⎛Δ

−=( )

⎟⎠⎞

⎜⎝⎛+=

1.0yearstlog2.01C 102

5.0

opp

p1.05.0zpI⎟⎟⎟

⎠

⎞

⎜⎜⎜

⎝

⎛Δ

+=

below)b(see

Plane Strain Lf/Bf ≥ 10

AxisymmetricLf/Bf =1

Lf = Length of footingBf = least width of footing

op

oppBf /2 (for axisymmetric case)Bf (for plane strain case)

Bf

oppp −=Δ

Depth to Peak Strain Influence Factor, Izp

Example 8Example 8--22ggGiven: 6’x24’ footing on soil profile shown Given: 6’x24’ footing on soil profile shown

below. Determine settlement at end of below. Determine settlement at end of construction and 10 years after constructionconstruction and 10 years after construction

Clayey Silt

Sandy Silt

Coarse Sand

Sandy Gravel

γt = 115 pcf; N160 = 8

γt = 125 pcf; N160 = 25

γt = 120 pcf; N160 = 30

γt = 128 pcf; N160 = 68

3 ft

3 ft

5 ft

25 ft

Bf = 6 ft

Ground Surface

Draw Strain Influence DiagramDraw Strain Influence Diagram

ggCalculate peak Calculate peak IzIz = 0.64= 0.64Plane Strain Lf/Bf ≥ 10

AxisymmetricLf/Bf =1

0

4

8

12

16

20

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7Influence Factor (Iz)

0

4

8

12

16

200.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7

Influence Factor (Iz)

Dep

th b

elow

foot

ing B

2B

3B

Strain Influence DiagramStrain Influence DiagramDivide into layersDivide into layers

0

4

8

12

16

20

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7Influence Factor (Iz)

0

4

8

12

16

200.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7

Influence Factor (Iz)

Dep

th b

elow

foot

ing

(ft)

Layer 1

Layer 2

Layer 3

Layer 4

Determine Elastic Modulus, EDetermine Elastic Modulus, Ess

ggUse Table 5Use Table 5--20, Page 520, Page 5--9090

ggCalculate XCalculate X--factor, X = 1.42factor, X = 1.42

Layer 1: Sandy Silt: E = 4N160 tsf Layer 2: Coarse Sand: E = 10N160 tsf Layer 3: Coarse Sand: E = 10N160 tsf Layer 4: Sandy Gravel: E = 12N160 tsf

Setup Table for Settlement Setup Table for Settlement ComputationComputation

Layer Hc N160 E XE Z1 IZ at Zi

(inches) (tsf) (tsf) (ft) (in/tsf)

1 36 25 100 142 1.5 0.31 0.07592 12 30 300 426 3.5 0.56 0.01523 48 30 300 426 6 0.55 0.05994 96 68 816 1,159 12 0.22 0.0176

Σ Hi= 0.1686

cZ

i HXEI

H =

Compute Correction Factors CCompute Correction Factors C11 , C, C22

ggAt end of construction, t=0.1 yearAt end of construction, t=0.1 year

ggAt t=10 yearsAt t=10 years

0.896psf1655

pcf115ft30.51Δpp

0.51C o1 =⎟⎟

⎠

⎞⎜⎜⎝

⎛ ×−=⎟⎟

⎠

⎞⎜⎜⎝

⎛−=

( )⎟⎠⎞

⎜⎝⎛+=

1.0yearstlog2.01C 102

0.11.01.0log2.01C 102 =⎟

⎠⎞

⎜⎝⎛+=

4.11.0

10log2.01C 102 =⎟⎠⎞

⎜⎝⎛+=

Determine Immediate SettlementDetermine Immediate Settlement

ggAt end of construction, t = 0.1 yearAt end of construction, t = 0.1 year

ggAt t = 10 yearsAt t = 10 years

( )( )

inches125.0S

tsfin1686.0

tsfpsf2000

psf16550.1896.0S

HpCCS

i

i

i21i

=

⎟⎠⎞

⎜⎝⎛

⎟⎟⎟

⎠

⎞

⎜⎜⎜

⎝

⎛=

Δ= ∑

inches175.00.14.1inches125.0Si =⎟

⎠⎞

⎜⎝⎛=

Consolidation SettlementConsolidation Settlement

ggSame procedures as in Chapter 7 (Approach Same procedures as in Chapter 7 (Approach Roadway Deformations)Roadway Deformations)


gg Calculate consolidation settlement for following case:Calculate consolidation settlement for following case:130 kips

Rock

Normally consolidated clay γsub = 65 pcf, e0 = 0.75, Cc = 0.410′

4′

10′

GravelγT = 130 pcf

Example 8Example 8--33p0 = (14′ × 130 pcf) + (5′ × 65 pcf) = 2,145 psf

psf208ksf0.208ft625

130kipsft)15ft(10

kips130Δp 2 ===+

=

⎟⎟⎠

⎞⎜⎜⎝

⎛ ++

=0

010

0

c

pΔpp

loge1

CHΔH

⎟⎟⎠

⎞⎜⎜⎝

⎛ +⎟⎠⎞

⎜⎝⎛

+=Δ

psf2145psf208psf2145log

0.7510.410ftH 10

″=′=Δ 1.109.0H


ggFind footing settlement (immediate + Find footing settlement (immediate + consolidation) for the following caseconsolidation) for the following case

Sand and Gravel Avg. N′ = 40

5′

25′

45′Clayey Silt CC = 0.25e0 = 0.90

(Normally Consolidated)

Student Exercise 6Student Exercise 6Pressure - psf

Dep

th –

ft.

Spread Footings on EmbankmentsSpread Footings on Embankments

ggSection 8.6Section 8.6gg If spread footings are placed on If spread footings are placed on

embankments, structural fills that include embankments, structural fills that include sand and gravel sized particles should be sand and gravel sized particles should be used that are compacted properly (minimum used that are compacted properly (minimum 95% of standard Proctor energy)95% of standard Proctor energy)

Settlement of Footings on Structural Settlement of Footings on Structural FillsFillsgg In absence of other data, use N1In absence of other data, use N16060 = 32 for = 32 for

the structural to estimate settlement of the structural to estimate settlement of footings on compacted structural fillfootings on compacted structural fill

Vertical Stress DistributionVertical Stress Distribution

Vertical StressVertical StressVertical Stress0 1 2 3 4 50 1 2 3 4 0 1 2 3 4 55

Dep

thD

epth

Bridge PierBridge PierBridge Pier

Earth Embankment

Earth Earth EmbankmentEmbankment

h=20’h=20’h=20’ h=40’h=40’h=40’

0

20

40

60

80

100

Footings on Footings on IGMsIGMs and Rocksand Rocks

ggUse theory of elasticityUse theory of elasticity

m

2fd

v E)1(BpC ν−Δ

=δ

where: δv = vertical settlement at surface Cd = shape and rigidity factors (Table 8-12) Δp = change in stress at top of rock surface due to applied footing load Bf = footing width or diameter ν = Poisson’s ratio (refer to Table 5-23 in Chapter 5) Em = Young’s modulus of rock mass (see Section 5.12.3 in Chapter 5)

Effect of Effect of Deformations on Deformations on Bridge Bridge StructuresStructuresggSection 8.9Section 8.9

Tilt (Rotation)

Differential Settlement

Differential Settlement

Tolerable Movements for BridgesTolerable Movements for Bridges(Table 8(Table 8--13)13)

Limiting Angular Distortion, δ/S

Type of Bridge

0.004 Multiple-span (continuous span) bridges

0.005 Single-span bridges

Note: δ is differential settlement, S is the span length. The quantity, δ/S, is dimensionless and is applicable when the same units are used for δand S, i.e., if δ is expressed in inches then S should also be expressed in inches.

Construction Point Concept for Construction Point Concept for Evaluation of SettlementsEvaluation of SettlementsggDivide the loadings based on sequence of Divide the loadings based on sequence of

constructionconstructionggKey construction point is when the final load Key construction point is when the final load

bearing member is constructed, e.g., when a bearing member is constructed, e.g., when a bridge deck is constructedbridge deck is constructed

ggTable 8Table 8--1414-- Put in a slidePut in a slide


ggAt the end of this session, the participant will At the end of this session, the participant will be able to:be able to:-- Calculate immediate settlements in granular Calculate immediate settlements in granular

soilssoils-- Calculate consolidation settlements in saturated Calculate consolidation settlements in saturated

finefine--grained soilsgrained soils-- Describe tolerances and consequences of Describe tolerances and consequences of

deformations on bridge structuresdeformations on bridge structures



SOILSAND

FOUNDATIONS


Lesson 08 Lesson 08 -- Topic 3Topic 3ConstructionConstruction

Section 8.10Section 8.10


ggAt the end of this session, the participant will At the end of this session, the participant will be able to:be able to:-- Discuss elements of shallow foundation Discuss elements of shallow foundation

construction/inspectionconstruction/inspection

Key Elements of Shallow Foundation Key Elements of Shallow Foundation ConstructionConstructionggTable 8Table 8--1515

ggContractor setContractor set--upupggExcavationExcavationggShallow foundationShallow foundationggPost installationPost installation

-- MonitoringMonitoring

Structural FillStructural Fill

ggTests for gradation and durability of fill at Tests for gradation and durability of fill at sufficient frequency to ensure that the sufficient frequency to ensure that the material meets the specificationmaterial meets the specification

ggCompaction testsCompaction testsgg If surcharge fill is used for preIf surcharge fill is used for pre--loading verify loading verify

the unit weight of surchargethe unit weight of surcharge

MonitoringMonitoring

ggCheck elevations of footing, particularly Check elevations of footing, particularly when footings are on embankment fillswhen footings are on embankment fills

ggPeriodic surveying during the service life of Periodic surveying during the service life of the footing, particularly if the subsurface has the footing, particularly if the subsurface has soft soils within the depth of influencesoft soils within the depth of influence

gg Impacts on neighboring facilitiesImpacts on neighboring facilitiesggUse instrumentation as necessaryUse instrumentation as necessary


ggAt the end of this session, the participant will At the end of this session, the participant will be able to:be able to:-- Discuss elements of shallow foundation Discuss elements of shallow foundation

construction/inspectionconstruction/inspection



SOILSAND

FOUNDATIONS

Interstate 0 Interstate 0 –– Apple FreewayApple FreewayNote: Scale shown in Station FormNote: Scale shown in Station Form

Baseline Stationing

Baseline Stationing

S.B. Apple Frwy

N.B. Apple Frwy

Proposed Toe of SlopeProposed Toe of Slope

Existing Ground SurfaceExisting Ground Surface

12

Proposed Final GradeProposed Final GradeProposed AbutmentProposed Abutment

Interstate 0Interstate 0

9090 9191 9292 9393

Apple Freeway Apple Freeway ExerciseExerciseggAppendix AAppendix A

-- Section A.7Section A.7

Subsurface Investigations

Terrain reconnaissance Site inspection Subsurface borings

Basic Soil Properties Visual description

Classification tests Soil profile

Laboratory Testing Po diagram

Test request Consolidation results Strength results

Slope Stability

Design soil profile Circular arc analysis Sliding block analysis Lateral squeeze analysis

Approach Roadway Settlement

Design soil profile Magnitude and rate of settlement Surcharge Vertical drains

Spread Footing Design

Design soil profile Pier bearing capacity Pier settlement Abutment settlement Surcharge Vertical drains

Driven Pile Design Design soil profile

Static analysis – pier Pipe pile H – pile Static analysis – abutment Pipe pile H – pile Driving resistance Lateral movement - abutment

Construction Monitoring

Wave equation Hammer approval Embankment instrumentation

″N″

7′

46112122403733

BAF -2

Clay

15′10′

4′

Sand

Assumptions: • Footing embeded 4′ below ground • Footing width = 1/3 pier height = 7′ • Footing length = 100′ L/W = 100/7 > 9 ∴Continuous

APPLE FREEWAYAPPLE FREEWAY

PIER BEARING CAPACITYPIER BEARING CAPACITY

″N″

7′

46112122403733

BAF -2

Clay

15′10′

4′

Sand

″N″

7′

46112122403733

BAF -2

Clay

15′10′

4′

Sand

7′

46112122403733

BAF -2

Clay

15′10′

4′

Sand

7′

46112122403733

BAF -2

Clay

15′10′

4′

Sand

7′

46112122403733

BAF -2

Clay

15′10′

4′

Sand

46112122403733

BAF -2

Clay

15′10′

4′

Sand

Assumptions: • Footing embeded 4′ below ground • Footing width = 1/3 pier height = 7′ • Footing length = 100′ L/W = 100/7 > 9 ∴Continuous


PIER BEARING CAPACITYPIER BEARING CAPACITY

10

Compute N1Compute N16060 valuesvalues

Depth (ft.)

p0

(psf) p0

(tsf) N

(bpf) Hammer

Efficiency (Ef) Ef / 60

N60

(bpf) Cn

N160 (bpf)

5 550 0.275 11 65 1.083 12 1.43 17 7 770 0.385 21 65 1.083 23 1.32 30 8 880 0.440 22 65 1.083 24 1.28 30 10 1100 0.550 40 65 1.083 43 1.20 52 12 1195 0.598 37 65 1.083 40 1.17 47 14 1290 0.645 33 65 1.083 36 1.15 41

Average corrected blow count = 36

APPLE FREEWAY PIER SETTLEMENTAPPLE FREEWAY PIER SETTLEMENT

Time (days)

Δ H

3″

2″

1″

25020015010050

Δ H = 2.85″

SANDSAND

CLAY CLAY --11

CLAYCLAY--22

APPLE FREEWAY PIER SETTLEMENTAPPLE FREEWAY PIER SETTLEMENT

Time (days)

Δ H

3″

2″

1″

25020015010050

Δ H = 2.85″

Time (days)

Δ H

3″

2″

1″

25020015010050

Δ H = 2.85″

SANDSAND

CLAY CLAY --11

CLAYCLAY--22

SANDSAND

CLAY CLAY --11

CLAYCLAY--22

APPLE FREEWAY APPLE FREEWAY

EAST ABUTMENT SETTLEMENTEAST ABUTMENT SETTLEMENT

Pf

Po

Pabut

Pc

10′

20′

30′

40′

1000 2000 3000 4000 5000 6000

Pressure (psf)

0

4920 5850

62005650

55504470

Gravel Layer

Clay

Sand

50′

Time (days)

0

Δ H2″

1″

500400300200100

Δ H = 2.59″

Dep

th (f

t)D

epth

(ft)

APPLE FREEWAY APPLE FREEWAY

EAST ABUTMENT SETTLEMENTEAST ABUTMENT SETTLEMENT

Pf

Po

Pabut

Pc

10′

20′

30′

40′

1000 2000 3000 4000 5000 6000

Pressure (psf)

0

4920 5850

62005650

55504470

Gravel Layer

Clay

Sand

50′

Time (days)

0

Δ H2″

1″

500400300200100

Δ H = 2.59″

Dep

th (f

t)D

epth

(ft)

Pf

Po

Pabut

Pc

10′

20′

30′

40′

1000 2000 3000 4000 5000 6000

Pressure (psf)

0

4920 5850

62005650

55504470

Gravel Layer

Clay

Sand

50′

Time (days)

0

Δ H2″

1″

500400300200100

Δ H = 2.59″

Dep

th (f

t)D

epth

(ft)

ΔHABUT

12.66″ emb. Δ

0

Δ H

15″

10″

5″

Time – days

400300200100

15.25″ Emb. + Abut

Assume Wick Drains Installed

*0.25″ Δ Remaining 30 days after abutment loaded

Begin Abutment Footing Construction


EAST ABUTMENT SETTLEMENT TREATMENTEAST ABUTMENT SETTLEMENT TREATMENT

15.25″Total ΔH

30′ Fill to 10′ Surcharge

0.83″

13.7″ t90

Time – Days

ΔH –Total

*Assume 10′Surcharge Used

240 days 400 days

15″

10″

5″

0100 200 300 500400

ΔHABUT

12.66″ emb. Δ

0

Δ H

15″

10″

5″

Time – days

400300200100

15.25″ Emb. + Abut




ΔHABUT

12.66″ emb. Δ

0

Δ H

15″

10″

5″

Time – days

400300200100

15.25″ Emb. + Abut




ΔHABUT

12.66″ emb. Δ

0

Δ H

15″

10″

5″

Time – days

400300200100

15.25″ Emb. + Abut





EAST ABUTMENT SETTLEMENT TREATMENTEAST ABUTMENT SETTLEMENT TREATMENT

15.25″Total ΔH


0.83″

13.7″ t90

Time – Days

ΔH –Total


240 days 400 days

15″

10″

5″

0100 200 300 500400

15.25″Total ΔH


0.83″

13.7″ t90

Time – Days

ΔH –Total


240 days 400 days

15″

10″

5″

0100 200 300 500400


0.83″

13.7″ t90

Time – Days

ΔH –Total


240 days 400 days

15″

10″

5″

0100 200 300 500400

Design Soil Profile

Strength and consolidation values selected for all soil layers. Footing elevation and width chosen.

Pier Bearing Capacity

Qallowable = 3 tons/sq.ft.

Pier Settlement

Settlement = 2.8", t90 = 220 days.

Abutment Settlement

Settlement - 2.6", t90 = 433 days.

Vertical Drains

t90 = 60 days - could reduce settlement to 0.25" after abutmentconstructed and loaded.

Surcharge

10' surcharge: t90 = 240 daysbefore abutment constructed.

SPREAD FOOTING DESIGNSPREAD FOOTING DESIGN

Design Soil Profile

Strength and consolidation values selected for all soil layers. Footing elevation and width chosen.

Pier Bearing Capacity

Qallowable = 3 tons/sq.ft.

Pier Settlement

Settlement = 2.8", t90 = 220 days.

Abutment Settlement

Settlement - 2.6", t90 = 433 days.

Vertical Drains

t90 = 60 days - could reduce settlement to 0.25" after abutmentconstructed and loaded.

Surcharge

10' surcharge: t90 = 240 daysbefore abutment constructed.

SPREAD FOOTING DESIGNSPREAD FOOTING DESIGN



SOILSAND

FOUNDATIONS

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