Calculation of heave of deep pier foundations
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Calculation of Heave of Deep Pier Foundations. By John D. Nelson, Ph.D., P.E., Hon. M. SEAGS, F. ASCE, Kuo-Chieh (Geoff) Chao, Ph.D., P.E., M. SEAGS, M. ASCE, Daniel D. Overton, M.S., P.E ., F. ASCE, and Robert W. Schaut, M.S., P.E ., M. ASCE . www.enganalytics.com. August 2012.

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Calculation of Heave of Deep Pier Foundations

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Calculation of heave of deep pier foundations

Calculation of Heave of Deep Pier Foundations

By

John D. Nelson, Ph.D., P.E., Hon. M. SEAGS, F. ASCE,

Kuo-Chieh (Geoff) Chao, Ph.D., P.E., M. SEAGS, M. ASCE,

Daniel D. Overton, M.S., P.E., F. ASCE,

and

Robert W. Schaut, M.S., P.E., M. ASCE

www.enganalytics.com

August 2012


Damage from expansive soils

Photo of Shear Failure in South Side of Pier at N7

DAMAGE FROM EXPANSIVE SOILS


Outline of presentation

Outline of Presentation

  • Introduction

  • Free-Field Heave Prediction

  • Pier Heave Prediction

  • Validation of APEX

  • Pier Design Curves

  • Example Foundation Design

  • Conclusions


Introduction

INTRODUCTION

  • Pier and grade beam foundations are a commonly used foundation type in highly expansive soils.

  • Existing pier design methods consider relatively uniform soil profiles, and piers with length to diameter ratios of about 20 or less.

  • Fundamental parameter on which foundation design is based is the “Free-Field Heave“(i.e. the heave of the ground surface with no applied loads)

  • A finite element method of analysis (APEX) was developed to compute pier movement in expansive soils having:

    • Variable Soil Profiles,

    • Complex Wetting Profiles,

    • Large Length-to-Diameter Ratios, and

    • Complex Pier Configurations and Materials


Free field heave prediction

FREE-FIELD HEAVE PREDICTION


Free field heave prediction by o edometer method

FREE-FIELD HEAVE PREDICTIONby Oedometer Method

Terminology and notation for oedometer tests


Free field heave prediction determination of heave index c h

FREE-FIELD HEAVE PREDICTIONDetermination of Heave Index, CH

Vertical stress states in soil profile


Free field heave prediction stress paths under different loading conditions

FREE-FIELD HEAVE PREDICTIONStress Paths Under Different Loading Conditions

S%

S

E

M

CH

CS

0

D

C

L

Cc

J

K

s’i

H

ho

hC1

LOG h

0’

s’i1

G

B

P

s’i2

F

A

s’CV

N

s’CS

LOG s’


Calculation of heave of deep pier foundations

  • FREE-FIELD HEAVE PREDICTIONDetermination of Heave Index, CH


Free field heave prediction calculations of design heave

FREE-FIELD HEAVE PREDICTIONCalculations of Design Heave

(S%)z

σ‘vo


Free field heave prediction determination of heave index c h1

FREE-FIELD HEAVE PREDICTIONDetermination of Heave Index, CH


Free field heave prediction determination of heave index c h2

FREE-FIELD HEAVE PREDICTIONDetermination of Heave Index, CH

Data from Method A of the ASTM D4546-08 Standard


Free field heave prediction determination of heave index c h3

FREE-FIELD HEAVE PREDICTIONDetermination of Heave Index, CH

Method A data from the Standard plotted in semi-log form


Free field heave prediction determination of heave index c h4

FREE-FIELD HEAVE PREDICTIONDetermination of Heave Index, CH

Method A data from the Standard plotted in semi-log form


Free field heave prediction relationship between s cv and s cs

FREE-FIELD HEAVE PREDICTIONRelationship between s′cv and s′cs

Logarithmic Form:

  • Data collected from Porter, 1977; Reichler, 1997; Feng et al., 1998; Bonner, 1998; Fredlund, 2004; Thompson et al. 2006; and Al-Mhaidib, 2006

  • The types of the soils consist of claystone, weathered claystone, clay, clay fill, and sand-bentonite

  • l = 0.36 to 0.90 (avg = 0.62) for claystone

    = 0.36 to 0.97 (avg = 0.59) for all soil types


Free field heave prediction relationship between s cv and s cs1

FREE-FIELD HEAVE PREDICTIONRelationship between s′cv and s′cs

Histograms of the λ values determined using the logarithmic form


Pier heave prediction

PIER HEAVE PREDICTION

Typical pier and grade beam foundation system


Damage from expansive soils1

DAMAGE FROM EXPANSIVE SOILS

Diagonal Crack

Pier


Pier heave prediction rigid pier analysis

PIER HEAVE PREDICTIONRigid Pier Analysis

Rigid Pier Analysis

Pdl

U

D


Pier heave prediction elastic pier analysis

PIER HEAVE PREDICTIONElastic Pier Analysis

Normalized Pier Heave vs. L/ZAD

Ref: Poulos & Davis (1980)

Nelson & Miller (1992)

Nelson, Chao & Overton (2007)

Straight Shaft

Belled Pier


Pier heave prediction elastic pier analysis1

PIER HEAVE PREDICTIONElastic Pier Analysis

Normalized Force vs. L/ZAD

Ref: Poulos & Davis (1980)

Nelson & Miller (1992)

Nelson, Chao & Overton (2007)

Straight Shaft

Belled Pier


Pier heave prediction apex method

PIER HEAVE PREDICTIONAPEX Method

Analysis of Piers in EXpansivesoils


Pier heave prediction apex method1

PIER HEAVE PREDICTIONAPEX Method

The field equations with soil swelling

where: eiso= isotropic swelling strain,

err, eqq, ezz = components of stress and strain in cylindrical coordinates, and

E = modulus of elasticity of the soil


Pier heave prediction apex method2

PIER HEAVE PREDICTIONAPEX Method

Interface Conditions

where:

Ft= the nodal force tangent to pier,

Hp= the pier heave,

Ut= the nodal displacement tangent to pier, and

k = the parameter used to adjust shear stress

soil boundary conditions

pier-soil boundary conditions


Pier heave prediction apex method3

PIER HEAVE PREDICTIONAPEX Method

Adjustment in pier heave

soil heave-upward force on pier

soil heave-upward force on pier

initial-no force on pier


Pier heave prediction apex method4

PIER HEAVE PREDICTIONAPEX Method

Soil failure and shear strain

Strength envelopes for slip and soil failure modes


Pier heave prediction apex method5

PIER HEAVE PREDICTIONAPEX Method

APEX Input

  • E = modulus of elasticity

  • a = coeff. of adhesion

  • ρi = cumulative free-field heave

  • ZAD= design active zone

  • d = diameter of pier

  • Pdl = dead load


Pier heave prediction apex method6

PIER HEAVE PREDICTIONAPEX Method

Typical APEX results

Shear Stress Distribution Along Pier

Variation of Slip Along Pier


Pier heave prediction apex method7

PIER HEAVE PREDICTIONAPEX Method

Typical APEX results

Axial Tensile Force (KN)

(d)

Axial Force Distribution


Validation of apex

VALIDATION OF APEX

  • Case I Manufacturing Building in Colorado, USA

  • Case II Colorado State University (CSU) Expansive Soil Test Site


Validation of apex1

VALIDATION OF APEX

Soil heave distribution for Cases I and II

Case I Manufacturing Building

Case II CSU Expansive Soil Test Site


Validation of apex2

VALIDATION OF APEX

Elevation survey data in hyperbolic form compared with heave computed by APEX for Manufacturing Building


Validation of apex3

VALIDATION OF APEX

Measured versus predicted axial force in the concrete pier for the CSU Test Site


Pier design curves

PIER DESIGN CURVES

Pier heave - linear free-field heave distribution


Pier design curves1

PIER DESIGN CURVES

Pier heave - linear free-field heave distribution


Pier design curves2

PIER DESIGN CURVES

Pier heave - nonlinear free-field heave distribution


Example foundation design

EXAMPLE FOUNDATION DESIGN

D = 300mm

0 m

Weathered Claystone

Free-field heave = 192 mm

Tolerable pier heave = 25 mm

a = 0.4

w = 12 %

g = 1.9 Mg/m3

  • Es = 9,400 kPa

  • S% = 2.0 %

  • s’cs = 350 kPa

5 m

Claystone

ZAD = 10 m

w = 9 %

g = 1.8 Mg/m3

Es = 11,200 kPa

S% = 3.5 %

s’cs = 550 kPa

10 m

Sandy Claystone

w = 8 %

g = 1.8 Mg/m3

Es = 120,000 kPa

S% = 1.86 %

s’cs = 305 kPa


Example foundation design1

EXAMPLE FOUNDATION DESIGN

Cumulative heave profile for example calculation

Weathered Claystone

Claystone

Sandy Claystone


Example foundation design2

EXAMPLE FOUNDATION DESIGN

Example pier heave computed from APEX program


Example foundation design3

EXAMPLE FOUNDATION DESIGN

APEX

(Uncased)

Rigid Pier

Elastic Pier

APEX (Cased)

0 m

0 m

Weathered Claystone

5 m

5 m

Claystone

10 m

10 m

Sandy Claystone

L = 11.4 m

15 m

15 m

L = 15.3 m

L = 18.0 m

L = 18.7 m

20 m

20 m

Tolerable pier heave = 25 mm

25 m

25 m


Conclusions

Conclusions

  • The rigid pier method assumes equilibrium of the pier, and hence, no pier movement, providing an overly conservative design.

  • The elastic pier method allows for some tolerable amount of pier heave. However, it is limited to use in simplified soil profiles and uniform piers.

  • The APEX program is a versatile and robust method of analysis.

  • APEX allows for pier analysis within complex soil profiles where soil properties and/or water contents vary with depth.

  • APEX generally predicts lower pier heave values, and shorter design lengths than other methods.


Calculation of heave of deep pier foundations

QUESTIONS?

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  • Fort Collins, Colorado 80525 USA

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