Shallow Foundations: Bearing Capacity and Settlement

363 Pages·1999·11.735 MB·English

by  Braja M. Das

SHALLOW
FOUNDATIONS
BBeeaarriinngg CCaappaacciittyy aanndd SSeettttlleemmeenntt
SHALLOW
FOUNDATIONS
BBeeaarriinngg CCaappaacciittyy aanndd SSeettttlleemmeenntt
Braja M. Das
CRC Press
Boca Raton London NewYo rk Washington, D.C.

PREFACE
Shallow Foundations: Bearing Capacity and Settlement is intended for use as
a reference book by university faculty members and graduate students in the
area of geotechnical engineering as well as by consulting engineers.
The text is divided into eight chapters. Chapters 2, 3, and 4 present the
various theories developed during the past fifty years for estimating the ultimate
bearing capacity of shallow foundations under various types of loading and
subsoil conditions.
Chapter 5 discusses the principles for estimating the settlement of
foundations—both elastic and consolidation. In order to calculate the founda-
tion settlement, it is desirable to know the principles for estimating the stress
increase in a soil mass supporting a foundation which carries the load trans-
mitted from the superstructure. These principles are also discussed in this
Chapter 5. Recent developments regarding the ultimate bearing capacity of
shallow foundations due to earthquake loading are presented in Chapter 6. Also
included in Chapter 6 are some details regarding the permanent founda-tion
settlement due to cyclic and transient loading derived from experimental
observations obtained from laboratory and field tests.
During the past fifteen years, steady progress has been made to evaluate
the possibility of using reinforcement in soil to increase the ultimate and
allowable bearing capacities of shallow foundations and also to reduce their
settlement under various types of loading conditions. The reinforcement
materials include galvanized steel strips, geotextile, and geogrid. Chapter 7
presents the state-of-the-art on this subject.
Shallow foundations (such as transmission tower foundations) are, on
some occasions, subjected to uplifting forces. The theories relating to the esti-
mation of the ultimate uplift capacity of shallow foundations in granular and
clay 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 know
from the users of the text if it serves the intended purpose.
Braja M. Das
Sacramento, 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 Failure
2.4 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 Soil
References
THREE ULTIMATE BEARING CAPACITY UNDER
INCLINED 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 Load
3.6 Ultimate Load on Rectangular Foundations
References
FOUR SPECIAL CASES OF SHALLOW FOUNDATIONS
4.1 Introduction
4.2 Foundation Supported by a Soil With a Rigid
Rough Base at a Limited Depth
4.3 Foundation on Layered Saturated Anisotropic
Clay ( ! = 0)
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 Trench
4.7 Shallow Foundations Above a Void
4.8 Foundations on a Slope
4.9 Foundations on Top of a Slope
References
FIVE SETTLEMENT AND ALLOWABLE BEARING
CAPACITY
5.1 Introduction
5.2 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 Area
5.6 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 Clay
5.10 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
Parameters
References
SIX DYNAMIC BEARING CAPACITY
AND SETTLEMENT
6.1 Introduction
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 Soil
Due 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 Foundation
References
SEVEN SHALLOW FOUNDATIONS ON
REINFORCED SOIL
7.1 Introduction
FOUNDATIONS ON METALLIC STRIP-REINFORCED
GRANULAR SOIL
7.2 Failure Mode
7.3 Force in Reinforcement Ties
7.4 Factor of Safety Against Tie Breaking
and Tie Pullout
7.5 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 BCR and BCR in Sand
u s
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 Theory
8.3 Theory of Meyerhof and Adams
8.4 Theory of Vesic 5
8.5 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 Safety
References
APPENDIX
Conversion Factors
CHAPTER 1
INTRODUCTION
1.1 SHALLOW FOUNDATIONS—GENERAL
The lowest part of a structure which transmits its weight to the underlying soil
or rock is the foundation. Foundations can be classified into two major cate-
gories: that is, shallow foundations and deep foundations. Individual footings
(Fig. 1.1) square or rectangular in plan which support columns, and strip
footings which support walls and other similar structures are generally referred
to as shallow foundations. Mat foundations, also considered shallow founda-
tions, are reinforced concrete slabs of considerable structural rigidity which
support a number of columns and wall loads. When the soil located immediate-
ly below a given structure is weak, the load of the structure may be transmitted
to a greater depth by piles and drilled shafts, which are considered deep
foundations. This book is a compilation of the theoretical and experimental
evaluations presently available in literature as they relate to the load-bearing
capacity and settlement of shallow foundations.
FIGURE 1.1 Individual footing