SHALLOWFOUNDATIONSBearing Capacity and SettlementBearing Capacity and Settlement

Boca Raton London New York Washington, D.C.CRC Press

SHALLOW FOUNDATIONSBearing Capacity and SettlementBearing Capacity and Settlement

Braja M. Das

PREFACE

Shallow Foundations: Bearing Capacity and Settlement is intended for use asa reference book by university faculty members and graduate students in thearea of geotechnical engineering as well as by consulting engineers.

The text is divided into eight chapters. Chapters 2, 3, and 4 present thevarious theories developed during the past fifty years for estimating the ultimatebearing capacity of shallow foundations under various types of loading andsubsoil conditions.

Chapter 5 discusses the principles for estimating the settlement offoundations—both elastic and consolidation. In order to calculate the founda-tion settlement, it is desirable to know the principles for estimating the stressincrease in a soil mass supporting a foundation which carries the load trans-mitted from the superstructure. These principles are also discussed in thisChapter 5. Recent developments regarding the ultimate bearing capacity ofshallow foundations due to earthquake loading are presented in Chapter 6. Alsoincluded in Chapter 6 are some details regarding the permanent founda-tionsettlement due to cyclic and transient loading derived from experimentalobservations obtained from laboratory and field tests.

During the past fifteen years, steady progress has been made to evaluatethe possibility of using reinforcement in soil to increase the ultimate andallowable bearing capacities of shallow foundations and also to reduce theirsettlement under various types of loading conditions. The reinforcementmaterials include galvanized steel strips, geotextile, and geogrid. Chapter 7presents the state-of-the-art on this subject.

Shallow foundations (such as transmission tower foundations) are, onsome occasions, subjected to uplifting forces. The theories relating to the esti-mation of the ultimate uplift capacity of shallow foundations in granular andclay soils are presented in Chapter 8.

Example problems to illustrate the theories are given in each chapter.I am grateful to my wife, Janice, for typing the manuscript in camera-

ready form and preparing the necessary artwork. It will be satisfying to knowfrom the users of the text if it serves the intended purpose.

Braja M. DasSacramento, California

To Janice and Valerie

CONTENTS

ONE INTRODUCTION 1.1 Shallow Foundations—General 1.2 Types of Failure in Soil at Ultimate Load 1.3 Settlement at Ultimate Load 1.4 Ultimate and Allowable Bearing Capacities References

TWO ULTIMATE BEARING CAPACITY THEORIES—CENTRIC VERTICAL LOADING 2.1 Introduction 2.2 Terzaghi’s Bearing Capacity Theory 2.3 Terzaghi’s Bearing Capacity Theory for

Local Shear Failure2.4 Meyerhof’s Bearing Capacity Theory 2.5 General Discussion on the Relationships

of Bearing Capacity Factors 2.6 Other Bearing Capacity Theories 2.7 Scale Effects on Bearing Capacity 2.8 Effect of Water Table 2.9 General Bearing Capacity Equation 2.10 Effect of Soil Compressibility 2.11 Bearing Capacity of Foundations on

Anisotropic Soil 2.12 Allowable Bearing Capacity With Respect

to Failure 2.13 Interference of Continuous Foundations in

Granular SoilReferences

THREE ULTIMATE BEARING CAPACITY UNDERINCLINED AND ECCENTRIC LOADS 3.1 Introduction

FOUNDATIONS SUBJECTED TO INCLINED LOAD

3.2 Meyerhof’s Theory (Continuous Foundation)3.3 General Bearing Capacity Equation 3.4 Other Results For Foundations With Centric

Inclined Load 3.5 Continuous Foundation With Eccentric Load3.6 Ultimate Load on Rectangular Foundations References

FOUR SPECIAL CASES OF SHALLOW FOUNDATIONS 4.1 Introduction4.2 Foundation Supported by a Soil With a Rigid

Rough Base at a Limited Depth 4.3 Foundation on Layered Saturated Anisotropic

Clay 4.4 Foundation on Layered c– Soil—Stronger Soil

Underlain by Weaker Soil 4.5 Foundation on Layered c– Soil—Weaker Soil

Underlain by a Stronger Soil 4.6 Continuous Foundation on Weak Clay With a

Granular Trench4.7 Shallow Foundations Above a Void4.8 Foundations on a Slope4.9 Foundations on Top of a Slope References

FIVE SETTLEMENT AND ALLOWABLE BEARINGCAPACITY 5.1 Introduction5.2 Stress Increase in Soil Due to Applied Load

ELASTIC SETTLEMENT

5.3 Flexible and Rigid Foundations 5.4 Settlement Under a Circular Area 5.5 Settlement Under a Rectangular Area5.6 Effect of a Rigid Base at a Limited Depth 5.7 Effect of Depth of Embedment 5.8 Elastic Parameters 5.9 Settlement of Foundations on Saturated Clay5.10 Settlement of Foundations on Sand 5.11 Field Plate Load Tests

CONSOLIDATION SETTLEMENT

5.12 General Principles of Consolidation Settlement 5.13 Relationships for Primary Consolidation

Settlement Calculation 5.14 Three-Dimensional Effect on Primary

Consolidation Settlement 5.15 Secondary Consolidation Settlement

DIFFERENTIAL SETTLEMENT

5.16 General Concepts of Differential Settlement 5.17 Limiting Values of Differential Settlement

ParametersReferences

SIX DYNAMIC BEARING CAPACITY AND SETTLEMENT 6.1 Introduction

( ! = 0) !

!

6.2 Effect of Load Velocity on Ultimate Bearing Capacity

6.3 Ultimate Bearing Capacity Under Earthquake Loading

6.4 Settlement of Foundations on Granular SoilDue to Earthquake Loading

6.5 Foundation Settlement Due to Cyclic Loading—Granular Soil

6.6 Foundation Settlement Due to Cyclic Loading in Saturated Clay

6.7 Settlement Due to Transient Load on FoundationReferences

SEVEN SHALLOW FOUNDATIONS ON REINFORCED SOIL7.1 Introduction

FOUNDATIONS ON METALLIC STRIP-REINFORCED

GRANULAR SOIL

7.2 Failure Mode7.3 Force in Reinforcement Ties7.4 Factor of Safety Against Tie Breaking

and Tie Pullout7.5 Design Procedure for a Continuous Foundation

FOUNDATIONS ON GEOTEXTILE-REINFORCED SOIL

7.6 Laboratory Model Test Results 7.7 Comments on Geotextile Reinforcement

FOUNDATIONS ON GEOGRID-REINFORCED SOIL

7.8 General Parameters 7.9 Relationships for Critical Nondimensional

Parameters for Foundations on Geogrid-Reinforced Sand

7.10 Relationship Between BCRu and BCRs in Sand 7.11 Critical Nondimensional Parameters for

Foundations on Geogrid-Reinforced Clay ( = 0 condition)

7.12 Bearing Capacity Theory 7.13 Settlement of Foundations on Geogrid-

Reinforced Soil Due to Cyclic Loading 7.14 Settlement Due to Impact Loading References

EIGHT UPLIFT CAPACITY OF SHALLOW FOUNDATIONS 8.1 Introduction

FOUNDATIONS IN SAND

8.2 Balla’s Theory8.3 Theory of Meyerhof and Adams

!

8.4 Theory of Vesic 58.5 Saeedy’s Theory 8.6 Discussion of Various Theories 8.7 Effect of Backfill on Uplift Capacity

FOUNDATIONS IN SATURATED CLAY

( = 0 CONDITION) 8.8 Ultimate Uplift Capacity—General 8.9 Vesic’s Theory 8.10 Meyerhof’s Theory 8.11 Modifications to Meyerhof’s Theory 8.12 Factor of SafetyReferences

APPENDIX Conversion Factors

!