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Design of Shallow Foundations

Samuel E. French, Ph.D., P .E.

ASCE PIIESS

180 l Alexander Beli Drive Reston, Virginia 20191~00

CONTENTS

PREFACE

T A 8 L E O F C O N V E R S l O N FA C T O R S ................... .. .................... l

PART l TYPES OF LOADS ANO TYPES OF SOILS

Chapter l Applications

Shallow Foundations in Modero Construction .................................................. 5 Common Types and Configurations of Buildings .......................... .................... 5 Common Types and Configurations of Foundations ......................................... 8 Common So il Pressures an d Settlements ......................................................... l O Standard Test Specifications ............................................................................ 12 Useful Approximations .................. ....................... ........................................... l2

Chapter 2 Gravity Loads on Foundations

Generai Categories of Loads o n Structures .................. ........................ ............ 15 Allowable Footing Pressures for Gravity Loads ..................... ......................... l5 Gravity Loads ............................................. ................................ ..................... 16 Distribution of Gravity Loads to Foundations ................................................ 20 Example Calculations ofGravity Loads on Footings ....................................... 23 Combinations of Gravity Loads ................ .. .... ........ ........................... .............. 26 Summary ofGravity Loads on Footings .................................... ...................... 27 Review Questions ................................. .. ...................................... ................... 27

Chapter 3 Lateral Loads on Foundations

Types of Latera! Loads ....................................................................... ............. 31 Stability under Combined Loading .................................................................. 32 Wind Velocities and Stagnation Pressures .......................... ............... ............... 34 Shape Factors for Wind Loads ........................................................................ .37 Calculation ofBase Shear due to Wind ............................................................ 39 Overtuming Moment due to Wind ....................... .... ........................................ 39 Earthquake Loads on Structures ....................................................................... 42 Seismic Risk Zones and Zone Factors .................... .. ................. .... .................. 43 Seismic Response of Building Systems ...................................... ...................... 45 Soil Profile Type fora Building Site ............................ ........ .. ...... .................... 45 Seismic Coefficient fora Structure ................................................................ .. .45 Calculation ofBase Shear due to Earthquake .................................................. .48 Overtuming Moment due to Earthquake .................................... .................... .49 Effect of Latera l Load on Footings of Rigid Frames ........................... .. ........... 53 Restoring Moment and Frictional Shear Resistance ..................................... .. .54

iii

Drift in a Rigid Frame ..................... .. ............................. .................................. 55 Corrections for Lateral Loads ......................................................................... 161 Summary ofFoundation Loads on a Rigid Frame .......................................... .56 Common Factors of Safety in Soils ................................................................ I64 Etfect ofLateral Load on Foundations ofBraced Frames .............................. .58 Use of a Reference Footing in Strength Calculations ...................................... I66 Drift in a Braced Frame ................................................................................... 58 Applications in Calculating Bearing Capacity ............................................... 168 Restoring Moment an d Frictional Shear Resistance ............ ............................ 59 Review Questions ...................................... .................................................... 175 Allowable Soil Pressures fora Braced Frame ... ................ ............................... 62 Summary ofFoundation Loads fora Braced Frame ............................. ........... 63 Chapter 7 Settlement or Foundations in a Soil Mass Load Combinations for Final Design ............... ................................................ 65 Applications in Determination ofDesign Loads ............................................. 66 Review Questions ........................... .. ............................................................... 70

Consolidation an d Settlement in Clays .......................................................... 181 Degree ofConsolidation ............................................ ..................................... l83 Overconsolidated Clay .................. ........................................ .. ....................... I86

Cbapter 4 Classifications and Properties or Soils The Consolidation Test for Clay Soils ........................... .... .. ........ .................. 188 Comparative Time-Consolidation Relationships ..... ............................... ....... 193

Broad So il Groupings ................... .... .............................. .................................. 75 Fragmentation and Settlement in Sands ............................................ .............. 20 l Response of a Soil to Foundation Loads ...................................................... .... 76 Review Questions ................................... ................................... .... ................ 203 Geologie Origins ofSoil.. ...................... ..... .......... ... ...................................... .... 78 Soil Profiles and Soil Horizons .................. ... .................................................... 79 Cbapter 8 Calculation or Settlements Grain Size and Distribution .............................................................................. 81 Plasticity an d Atterberg Limits ........................................................................ 84 Consistency and Textural Classification ofSoils ................... .......................... 87 Engineering Classification ofSoils ............................... ............. .................. ...... 88 lndex Properties of Soils ............. ..... .............................................................. .. 93 Review Questions ..................................................... .. ............................... ...... 98

Ditferential Settlements ............. ................................................... .................. 207 Reliability ofSettlement Calculations ............................................................ 207 Use of a Reference Footing in Settlement Calculations .................................. 208 Settlement CaJculations in Normally Consolidated Clays .............................. 213 Settlement Calculations in Overconsolidated Clays ....................... .... ... ......... 223 Settlement Calculations in Sands .................................................................... 234 Modulus ofSubgrade Reaction ............................ .. ........................................ 239

PART Il RESPONSE OF A SOIL MASS TO FOUNDATION LOADS Comparison of Response ofCiays and Sands to Load .................................. 240 Review Questions ......................................... .... ..... ............................ ............ 241

Cbapter 5 Strengtb and Pressure Dispersion in Soils

Permeability, Effective Stress and Submergence .................. ....................... .. l 05 PART 1H DESIGN OF SHALLOW FOUNDATIONS ON A SOl L MASS Measurement of the Shear Strength of Clays .......................................... ....... 108 Measurement of the Shear Strength of Sands ....... .. ............................. .. ... ...... ll3 The Coulomb Equation for the Strength ofSoils ........................ ................... 122 Dispersion of Load into a Soil Mass ......................... .......... ....................... .... l 22 Approximate Dispersion ofLoad into a Soil Mass .................................. ..... 127 Pressure Dispersion through Underlying Strata ............................................. l29 At-Rest Pressures in a Soil Mass ................................................................... 132 In Situ Properties of Soils ..................... .......................................... ................ l35 Review Questions ........................ ............ .. ................................................... . 136

Cbapter 9 Effects or Soii-Structure lnteraction

Summary of Allowable So il Pressures ..................... ....................... ............... 25 l Estimated Pressure-Settlement Relationships ................................................ 254 Etfects ofStructural Design on Foundation Design ....................................... 256 Footings with Vertical Load Only .................................................................. 256 Etfects ofColumn Moments on Footing Rotations ....................................... 257 Effects of Footing Rotations on Soil Pressure ....... ......................................... 259 Generalization of Effects of Rotations ...................... ..................................... 263

Cbapter 6 Calculation or Allowable Pressures

Levels of Accuracy ofthe Failure Analysis ................................................... 143 Ultimate Shear Failure in a Soil Mass .... ........................................................ l44 Allowable Bearing Strength ofa Soil Mass ..... ............................................... l48 Corrections for Shape ofFootings ........... ................................ .... .................. 158 Corrections for Depth of Founding .................................................... .. .......... 159 Corrections for Groundwater Level... ...... ...................................................... 160

Attachment ofColumns to Footings .............................................................. 266 Peak Pressure in Strength Calculations ............................................ .. .... ...... .. .268 Applications in Selecting Fina] Footing Sizes ................................................ 269 Presumptive Bearing Pressures ...................................................................... 277 Variations ofContact Pressures under a Footing ................................. .......... 279 Review Questions ............... ......... .. ... ...... ... ................... .. .................... ........... 281

iv v

Chapter lO Comparative Selection of Footing Sizes

lnteraction within a Group of Footings ......................................................... 285 Relative Settlements between Footings ....... .............. .............. ....................... 286 Applications in Selecting Footing Sizes .............. ........................................... 287 Effects ofCiose Proximity ............................. ................................................ 293 Effects of Unequal Loads ............................................................................... 296 Effects of Intermixed Footing Types ........... ...................... ............................ 298 Effects of Adjacent Excavations ........................................................ ............. 302 Review Questions .......................................................................................... 304

PART IV RELATED TOPICS LN FOUNDATION SYSTEMS

Chapter Il Otber Topics in Foundation Design

Special Design Conditions ............. ........................... ........................ ............. 313 Combined Footings ........................... ...... ..................................... .................. .3 13 Latera! Friction Loads on Footings ........................... .................................. ... 319 Foundations for Stucco or Decorative Masonry ........................................... .322 Unreinforced Foundations ................... ........................................ ............ ...... .323 Rubble or Masonry Foundations ................................... .......................... ...... 325 Treated Timber Foundations ........................................ ............... ...... ............ 326 Foundations on Expansive Clays ................... ........ ...... .................................. 328 Review Questions ............ .............................................................................. 332

Cbapter 12 Field Tests aod tbe Soils Report

lnitiation of a Soils lnvestigation ................ ................................................... 335 Preliminary Assessment ofSite ........................................... ................ .......... 337 Scope ofthe Site lnvestigation ....................................................................... 338 Field Sampling and Testing ........................... .......................... ... .......... .......... 348 Field Load-Settlement Tests .................... ............... .................. .. ................... 354 Common Laboratory Tests ........... ........................ ....... ... .............................. .357 The Soils Report ................................................................. ........................... 358 Review Questions ............................................... ........ ......... .... ...... .............. .. 360

Refereoces ...................................................................................... .................... 365

lndex .................................................................................................................... 369

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REFE R ENCE

l. Atterberg, A., Die Plastizat der Tone, lnternatmnale Mtllelfungenfur Bodenkunde, Vol.l ( 1911 ), pp. l 0-43

2. ACl Committee 318-89, Huildmg Code l?equirementsfor l?einfòrced ( ·oncrete, American Concrete lnstitute, Detroit, Mich., 1989

3. American Society ofCivi l Engineers, Suhswface !nvestigationfor Design and Construction ofBuildings, ASCE manual ofEngineering Practice 56, ASCE, New York, 1962

4.

5.

6.

7.

8.

9.

American Society ofCivi l Engineers Standard 7-93, Minimum Design /oadsfor Buildmgs and other Structures, ASCE, New York, 1994

Bazaraa, A. , lise ofthe Standard Penetraflon Test for Evtimating Selllemenls of Sha!low Foundations on Sand, Ph.D. Thesis, University of Illinois, 1967

Boussinesq, M. J., Application des Fotentiels, a 1'/:ì ude de l'f.q uilibre et du mouvement des So!ides 1!"/astiques, Gauthier-Villars, Paris, 1885

Brinch Hansen, J. , A Genera! Formula for Bearmg Capacity, Bulletin No. Il , Danish Geotechnical l nstitute, Copenhagen, 196 1

Brinch Hansen, J., A revised and Extended Formu!afor Bearing C'apacity, Bulletin No. 28, Danish Geotechnicallnstitute, Copenhagen, 1970

Casagrande, A. , Determination ofthe Preconsolidation Load and its Practical Signiticance, Proceedings. First lnternationa/ conf erence on Soi/ Mechanics and Foundation Engineering, Cambridge, Mass., Voi.J ( 1936), pp.60-64

l O. Casagrande, A. , Classitication and ldentitication of Soils, Transactions ofthe American Soctety ofOvil Engmeers, (19-18), pp. 901-902

Il . Chen, W. F., Limi/ Analysis and Soil Plasticity, Elsevier, Amsterdam, 1975

12. Das, B.M., Principles ofFoundation Engineering, 3rd ed., PWS Publishing Company, Boston, Mass, 1995

365

13 Eggested, /\., Deformation Measurements belo" a Model Footing on the Surface of Dry Sand, Proc:eedmg~ ojt!Je /:"uropean ( "onferenc:e on ,\'od Mechamc.\ und Foundatwnf:"ngmeenng, Wiesbaden Germany, Voi l , pg233, 1963

1-t. Fang, Hsai-Yang, (Ed.), Foundation Engineering l landbook, V an Nostrand Reinhold, New York, 199 1

15. French, S.E., Ftmdumentuls I!(Structurul Analysts, W est Publishing Company, St. Paul, Minn., 1995

16. Generai Services Administration, Structural Engineering, in <ì.\'A Hamlbook, PBS-P-3475.1 B, OSA, Washington, D.C.

17. Hvorslev, M.J. , Suhsurface l:xploration and Samplmr, of Soils f hr Ctvd /:'ngmeering Purposes. Waterways Experiment Station, Vicksburg, Mississippi, 1949

18. Hough, B. K., Basic Soi/s Enr.ineermg , 2nd ed., Ronald Press, New York, 1957

19. Holtz, Robert D., Pressure Distribution and Senlement of Shallow Foundations, in Foundation /:'ngineering Handbook. Winterkom, H.F., and H. Y. Fang, Eds., V an Nostrand Reinhold, New York, 1975, Chapter 3.

20. Huntington, W.C., and Mickadeit, R.E. , Building Construction Materials and Types ofof Construction, 5th ed., John Wiley, New York, 1981

21. lntemational Conference of Building Officials, Uniform Bwlding ('ode, ICBO, Whittier, Calif., 1994

22. lngra, T. S., and Beacher, G .B., Uncertainty in Bearing Capaci ty of Sands, AS('t.:: .Journa/ ofGeotechnical/:'ngmeering, 109, No. 7, pp. 899-914, 1983

23. Merritt, F. S. (ed.}, Bwlding IJestgn and ('onstructton Handhook, 5th ed., McG raw Hill , New York, 1994

24. Meyerhof, G. G.,The Ultimate Bearing Capacity of Foundations, Geotechnique, 2, No. 4, pp. 301 -332, 195 1

25. Meyerhof, G. G., The Bearing Capacity of Foundations under Eccentric and lnclined Loads, Proceedings, 3rd /ntem ationa/ Conf erence on Soil mechanics and Foundat ion J:'ngineering, Zurich, Voli, 1953

26. Meyerhof, G.G., Some Recent Research on the Bearing Capacity of Foundations, Canadian (ìeotechnica/.Journal, l., No. l , pp. 16-26, 1963

366

27 Meyerhof, G G , Safety Factors and L1mit States /\nal) s1s m Cìeotechmcal Engineenng, ( ìenteduuque, 21. pp. 1-7, 1984

28 Meycrhof, G G , and Fellenius, B H (eds ), ( 'wwdtwl 1-rnuulullon f:"ngmeermg Afanual, 2nd ed., Canadian Geotechnical Society, 1985

29 Mississippi State l lighway Department, A St uc~) ' of.-lctll'<' ( "fc~l '·' w Related tn Htglm·a.'' l>estgn, MSHD, Jackson, Miss., 1972

30. Nat10nal Forest Products Association, A/1-Weuther /Vood Fnunclatmn Sy.\lem: /)estgn, Fahm:afmn, ln., tal/utton Afwlltaf, NFPA, Washington, D.C 1982

31. Peck, R. B., Hansen, W.E., and Thornburn, T. H., 1-"rnmclatum /:'ngmeermg, 2nd ed., Wi ley, New York, 1974

32. Schmertmann, J.H., Static Cone to Compute Static Settlement over Sand, Journal 1ljtlte Sm/ Mechumcs and /·(nmdatum Otvi.\'ton, American Society of Civil Engineers, Vol. 96, SM3, 1970, pp. 10 11 - 1043

33. Schmertmann, J.H., and Hartman, J.P., lmproved Stra in lnnuence Factor Diagrams, ./o urna/ of the ( ;eotechmca/ h"ngmeering Otl'isum, American Society ofCivil Engineers, Vol. 104, GT8, 1978, pp. 1131-11 35

34. Skempton, A. W., Notes on the Compressibil ity of Clays, Quarter~l' Journal ofGeologtcal Soctety , London, Vol. C ( 1944 }, pp. l 19-1 35

35. Southem Building Code Congress lnternational, Standurd lJwldmg ('ode, SBCCI, Birmingham, Alabama, 1994

36. Sowers, G.F., lntroductory Soil Mechanics and Foundutton.,·: ( ìeoteclmica/ l:'ng ineenng, 4th ed., Macmillan, New York, 1979

37. Teng, T.C., and Clisby, M.B., Experimental work for Active Clays in Mississippi, Tramportafwn!:'ngineering Journal. AS( '/:', Proceedmgs, Vol. 10 1 No. TE I, 1975

38. Terzaghi, K., and Peck, R. B., Soi/ Mechumcs in f:'ngineering fJracftc:e, Wiley, New York, 1967

39. U.S. Department ofthe Navy, Design Manuai--Soil Mechanics, Foundations and Earth Structures, NA VFA( ' IJM- 7, U.S. Govemment Printing Office, Washington, D.C. , 197 1

40. U.S. Department ofthe Navy, Soil Mechanics, NAV!·'A( ' IJA/ 7. 1, U.S. Govemment Printing Office, Washington, D.C. , 1982

367

-Il U.S Department ofthe Navy, Structura_l Engineering, NA I' I·A< · I>M-2. lJ .S Government Printing Office, Washington, D.C., 1983

42 Vesic, A.S., Analysis of Ultimate Loads of Shallow Foundations, .lo urna/ of 1he .'•ì()f/ Atedrwuc:s wrd Fmmdatron.1 /Jrvrsron, American Society of Civil Engineers, Vol. 99, No. SMI , pp 45-73, 1973

43. Vesic, A. S., Bearing Capacity ofShal low Foundations, Fmmdatron /:·n,l!,meerrng 1/anc/hook, 1st ed. H. F Winterkorn and H. Y. Fang (eds.), Chapter 3, Van Nostrand Reinhold, New York, 1975

368

AASHTO. 12 ACl , 12

A

ACl approximate method, 20 accuracy

of failure analysis. 143 of selllement calculations, 207

A-line (Activity Line), 87 active clays, l l. 87. 328 allowable bearing pressures

for braced fi-ames, 15, 33, 62 fro m classilications, 88 gravity plus latera!. 33. 252 presumptive. 277 for rigid frames, 33, 56 summary of, 252

allowable bearing strength, 143, 148 computation of, 33, 152, 252 derivation of, 144

angle of internai friction, 11 5 apprmomations

of constants, 12 of pressure bulbs. 127 size-sertlement ratios, 128, 208 of shear failure mode, 148

applications and calculations selecting footing sizes, 269. 287

ASTM, 12, 80, 357 at-rest pressures, 132 auachments, columns to footings, 266

typical designs, 266 Allerberg limits, 84 augers, 349

B

base shear distribution of, 32, 39, 49 earthquake, 32. 49 example calculations, 40, 50 wind, 32, 40

bcaring capacity calculation of, 153, 168, 252 corrections for, 156 factors, 141 , Table 6- 1 at failure, 148

Boussinesq pressure bulb, 122 abbreviate<!, 124 approximate. 127 overlapping, 129, 293, 296

building codes, 3 1, 34, 37, 43, 48 buildings, types, 5 building systems, 45 buoyancy, effects of, 105, 160

l N O E X

braced frames allowable soil pressures. 15, 33. 62 defined, 5 drift in, 58 effects of lateralloads o n, 58 footing loads in. 58

reference footing for, 166 selection of footings for. 273 summary of foundatio n loads, 63

c cantilever footing, 3 18 Casagrande plasticity chart. 87 casing, of test hole, 350 center of latera! forces

inertia, 32, 50 wind, 32, 40

classification of soils unified system, 88 consistency and textural. 87

clays activity in, l l appearance, 75, 181 cohesion in, 75, l 08, Il l . 122. 135 consolidation in, 181 . 188, 192 defined, 8 1, 87 desiccation in, 187, 328 expansive, li , 87, 328 failure ang le in, 109, 145 nocculent layup, 182 as group classification, 75, 90 honeycomb layup, 182 lightly consolidated, 227, 229 normally consolidate<!, 183, 213 overconsolidated, 186, 223 porewater in, 183 sensitive, 182. 188

coeflìcients of curvature, 84 ofuniformity. 84 seismic, 47

cohcsion, 75, l Il combined footings 295, 314 combined loads, 32, 56, 63 , 65 comparative s izing, 166, 286 compression index, 2 14, 226 compression tests, l 08

369

consolidate<! quick, 11 2 consolidated s low, 11 2 triaxial, l 09 unconfined, l l O unconsolidated quick, l l l