CIVE.4310 Shallow Foundation Settlement

Revised 03/2020

CIVE.4310 FOUNDATION & SOIL ENGINEERINGSHALLOW FOUNDATIONS - SETTLEMENT

Figures after Crawford, 1972 (CBD-148)

TYPES OF SETTLEMENTL L L

UniformSettlement

Tilt Non-UniformSettlement

DD

Where:

St = Total Settlement(Typically limited to 1 inch)

D = Maximum Differential SettlementL = Building (or Span) LengthDeflection Ratio = D/L

Table 2-1. Maximum Allowable St (EM 1110-1-1904)

St

Revised 03/2020


Figures after Crawford, 1972 (CBD-148)

TYPES OF SETTLEMENTL L L

UniformSettlement

Tilt Non-UniformSettlement

DD

Where:

St = Total SettlementD = Maximum Differential SettlementL = Building (or Span) LengthDeflection Ratio = D/L

Table 2-2. Limiting D/L (EM1110-1-1904)

St

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Figure 2-1. EM1110-1-1904

DIFFERENTIAL SETTLEMENT

Where:

D = Max. Differential Settlementd = Differential Settlement between 2 PtsL = Building (or Span) Lengthl = Length between 2 PointsAngular Distortion b = d/l

Differential Settlement

Interference w/ Adjacent StructuresDisruption of Machinery & PeopleCrackingJammed Floors & WindowsUneven FloorsReduction of waterstop efficiencyStructural Failure

Revised 03/2020


Figure 2-1. EM1110-1-1904


Table 2-3. Limiting b/l to Avoid Damage(EM1110-1-1904)

*Based on field surveys of damage

Revised 03/2020


Figure 2-1. EM1110-1-1904


Table 2-3. Empirical Correlations between D and b (EM1110-1-1904)

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Figure 1-3. EM1110-1-1904

FOUNDATION CONTACT PRESSURESRIGID FOUNDATIONS

Typically ExperienceUniform Settlement

FLEXIBLE FOUNDATIONSTypically Experience

Differential Settlement

Figure 12-14. Das FGE (2005)

Revised 03/2020


WHAT DO YOU NEED TO CALCULATE SETTLEMENT?

FOUNDATION SETTLEMENT COMPONENTS

Total Foundation Settlement = Elastic Settlement + Consolidation Settlement

a.k.a. Immediate.Primary Settlement Component

of Sands but also occurs inCohesive Soils.

a.k.a. Long-Term.Primary Settlement Component

of Cohesive Soils.Covered in Soil Mechanics

St = Se + Sc

Foundation Loads/PressuresChanges in Vertical Soil Stress (Ds)Foundation Size and LocationSoil ProfileSoil Properties:

Elastic Settlement: Es, mConsolidation Settlement: 1D Consolidation Test Data

Revised 03/2020


Boussinesq DistributionsFigure 1-2. EM 1110-1-1904

STRIP

VERTICAL STRESS INCREASE (Ds) IN SOILS (REVIEW)

SQUARE

Westergaard DistributionsFigure 11. NAVFAC DM7.01

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APPROXIMATE 2V:1H DISTRIBUTION METHOD

))(( zLzB

Q

Ds

Figure C-1. EM1110-1-1904

Where:

Ds = Change in Total VerticalStress

Q = Applied Foundation LoadB = Foundation WidthL = Foundation Length


Revised 03/2020


Table C-1. Boussinesq Solutions (EM 1110-1-1904).


Revised 03/2020



Table C-1. Boussinesq Solutions (EM 1110-1-1904).

Revised 03/2020


Figures courtesy of http://www.taunton.com

VERTICAL STRESS INCREASE (Ds) IN SOILS

Depth of Influence of Ds for Settlement Calculations

SQUARE: Depth = 2B STRIP: Depth = 4B

Revised 03/2020


VERTICAL STRESS INCREASE (Ds) IN SOILSDepth of Influence of Ds for Settlement Calculations

Revised 03/2020


21 1

21FFI

s

ss m

m

Se qo a ¢B( )1ms2

Es

IsI fWhere:

Se = Elastic Settlementqo = Contact Stressa = Foundation Location Factor

for Settlement under Centera = 1, m’ = L/B, n’ = H/(B/2)For Settlement under Cornera = 1, M’ = L/B, n’ = H/B

B’ = Widthuse B for Settlement @ Corneruse B/2 for Settlement @ Center

General Elastic Relation(Flexible Foundation):

ms = Soil Poisson’s RatioEs = Soil Elastic ModulusIs = Shape Factor

f(ms, F1, F2) – Table 12.3 Das FGE (2005)

If = Depth Factorf(Df/B, ms, L/B) – Table 12.4 Das FGE (2005)

General Elastic Relation(Rigid Foundation):

),(93.0 centerflexibleee SS

ELASTIC SETTLEMENT OF SOIL

Revised 03/2020


( )2/;'B

Hn

B

Lm ¢

ELASTIC SETTLEMENT OF SOIL – TABLE 12.3 Das (2005)

B

Hn

B

Lm ¢ ;'Center of

Footing:Corner ofFooting:

H = Depth to rigid layer

Revised 03/2020


ELASTIC SETTLEMENT OF SOIL – TABLE 12.4 Das (2005)

Revised 03/2020


ELASTIC PARAMETERS OF SOIL

Table 12.5. Typical Elastic Parameters of Soils(Das FGE (2005)

Table D-3. Typical Soil Elastic Moduli(EM1110-1-1904)

Revised 03/2020


Se qo(1n

2 ) ¢A144Esbz

Where:

Se = Elastic Settlementqo = Applied Vertical Stress (ksf)A’ = Effective Area of Footing (ft2)Es = Young’s Modulus of Soil (ksi)

(See Article 10.4.6.3 if directmeasurements are not available)

Elastic Half-SpaceMethod:

ELASTIC SETTLEMENT OF SOIL (AASHTO, 2010)

n = Soil Poisson’s Ratio(See Article 10.4.6.3 if directmeasurements are not available)

bz = Shape Factor (dimensionless)(As specified in Table 10.6.2.4.2-1)

Unless Es varies significantly with depth, Es should be determined at a depth of about ½ to 2/3 of B below the footing. If the soil modulus varies significantly with depth, a weighted average value of Es should be used.

Revised 03/2020


Figure courtesy of Marchetti (1999) - The Flat Dilatometer (DMT) andIt's Applications to Geotechnical Design

ELASTIC SETTLEMENT OF SOIL - DMT

Uses Direct Measurement of Soil to

Calculate Settlement

Revised 03/2020


DD

ZM

SDMT

es


Stress Distribution

Figure courtesy of Marchetti (1999) - The Flat Dilatometer (DMT) andIt's Applications to Geotechnical Design

Where:

Se = Elastic SettlementDs = Change in StressMDMT = Constrained ModulusZ = Depth

Revised 03/2020



Marchetti (1999) - The Flat Dilatometer (DMT) andIt's Applications to Geotechnical Design

Revised 03/2020


Figure from Hayes (1990)


Revised 03/2020


DMT SETTLEMENT EXAMPLE (NTS)

Depth(ft)

0

10.2GWT 10 ft

Silty Sand (SM)gt = 115 pcf, f' = 34°

3ft Sq. ColumnQ = 27 kips

Df = 1ft Df = 1ft

2ft x 4.5 ft Column FootingQ = 27 kips

Determine Settlement of Both Footings using the provided

DMT Data

Revised 03/2020


DMT SETTLEMENT

EXAMPLE

DMT Data

CIVE.4310 Shallow Foundation Settlement

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