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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.

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Calculation of Heave of Deep Pier Foundations

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  1. 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

  2. Photo of Shear Failure in South Side of Pier at N7 DAMAGE FROM EXPANSIVE SOILS

  3. Outline of Presentation • Introduction • Free-Field Heave Prediction • Pier Heave Prediction • Validation of APEX • Pier Design Curves • Example Foundation Design • Conclusions

  4. 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

  5. FREE-FIELD HEAVE PREDICTION

  6. FREE-FIELD HEAVE PREDICTIONby Oedometer Method Terminology and notation for oedometer tests

  7. FREE-FIELD HEAVE PREDICTIONDetermination of Heave Index, CH Vertical stress states in soil profile

  8. 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’

  9. FREE-FIELD HEAVE PREDICTIONDetermination of Heave Index, CH

  10. FREE-FIELD HEAVE PREDICTIONCalculations of Design Heave (S%)z σ‘vo

  11. FREE-FIELD HEAVE PREDICTIONDetermination of Heave Index, CH

  12. FREE-FIELD HEAVE PREDICTIONDetermination of Heave Index, CH Data from Method A of the ASTM D4546-08 Standard

  13. FREE-FIELD HEAVE PREDICTIONDetermination of Heave Index, CH Method A data from the Standard plotted in semi-log form

  14. FREE-FIELD HEAVE PREDICTIONDetermination of Heave Index, CH Method A data from the Standard plotted in semi-log form

  15. 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

  16. FREE-FIELD HEAVE PREDICTIONRelationship between s′cv and s′cs Histograms of the λ values determined using the logarithmic form

  17. PIER HEAVE PREDICTION Typical pier and grade beam foundation system

  18. DAMAGE FROM EXPANSIVE SOILS Diagonal Crack Pier

  19. PIER HEAVE PREDICTIONRigid Pier Analysis Rigid Pier Analysis Pdl U D

  20. 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

  21. 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

  22. PIER HEAVE PREDICTIONAPEX Method Analysis of Piers in EXpansivesoils

  23. 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

  24. 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

  25. 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

  26. PIER HEAVE PREDICTIONAPEX Method Soil failure and shear strain Strength envelopes for slip and soil failure modes

  27. 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

  28. PIER HEAVE PREDICTIONAPEX Method Typical APEX results Shear Stress Distribution Along Pier Variation of Slip Along Pier

  29. PIER HEAVE PREDICTIONAPEX Method Typical APEX results Axial Tensile Force (KN) (d) Axial Force Distribution

  30. VALIDATION OF APEX • Case I Manufacturing Building in Colorado, USA • Case II Colorado State University (CSU) Expansive Soil Test Site

  31. VALIDATION OF APEX Soil heave distribution for Cases I and II Case I Manufacturing Building Case II CSU Expansive Soil Test Site

  32. VALIDATION OF APEX Elevation survey data in hyperbolic form compared with heave computed by APEX for Manufacturing Building

  33. VALIDATION OF APEX Measured versus predicted axial force in the concrete pier for the CSU Test Site

  34. PIER DESIGN CURVES Pier heave - linear free-field heave distribution

  35. PIER DESIGN CURVES Pier heave - linear free-field heave distribution

  36. PIER DESIGN CURVES Pier heave - nonlinear free-field heave distribution

  37. 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

  38. EXAMPLE FOUNDATION DESIGN Cumulative heave profile for example calculation Weathered Claystone Claystone Sandy Claystone

  39. EXAMPLE FOUNDATION DESIGN Example pier heave computed from APEX program

  40. 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

  41. 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.

  42. QUESTIONS? • Engineering Analytics, Inc. • 1600 SpechtPoint Rd., Ste. 209 • Fort Collins, Colorado 80525 USA • Phone: 970-488-3111 • Fax: 970-488-3112 • www.enganalytics.com • Email: jnelson@enganalytics.com

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