Foundation Engineering for Expansive Soils

John D. Nelson, Kuo Chieh Chao, Daniel D. Overton, Erik J. Nelson

• Publisher: Wiley
• Year: 2015
• ISBN:
  9781118415290
• Edition: 1
• Topic: Technology & Engineering
• Subtopic: Civil Engineering
• Index: Technology & Engineering

Your guide to the design and construction of foundations on expansive soils

Foundation Engineering for Expansive Soils fills a significant gap in the current literature by presenting coverage of the design and construction of foundations for expansive soils. Written by an expert author team with nearly 70 years of combined industry experience, this important new work is the only modern guide to the subject, describing proven methods for identifying and analyzing expansive soils and developing foundation designs appropriate for specific locations.

Expansive soils are found worldwide and are the leading cause of damage to structural roads. The primary problem that arises with regard to expansive soils is that deformations are significantly greater than in non-expansive soils and the size and direction of the deformations are difficult to predict. Now, Foundation Engineering for Expansive Soils gives engineers and contractors coverage of this subject from a design perspective, rather than a theoretical one. Plus, they'll have access to case studies covering the design and construction of foundations on expansive salts from both commercial and residential projects.

• Provides a succinct introduction to the basics of expansive soils and their threats
• Includes information on both shallow and deep foundation design
• Profiles soil remediation techniques, backed-up with numerous case studies
• Covers the most commonly used laboratory tests and site investigation techniques used for establishing the physical properties of expansive soils

If you're a practicing civil engineer, geotechnical engineer or contractor, geologist, structural engineer, or an upper-level undergraduate or graduate student of one of these disciplines, Foundation Engineering for Expansive Soils is a must-have addition to your library of resources.

Chapter 1
Introduction

The design of foundations for structures constructed on expansive soils is a major challenge for geotechnical engineers practicing in areas where such soils are prevalent. The forces exerted by expansive soils and the movements that they cause to even heavily loaded structures can be well in excess of those experienced by ordinary soils. Also, the costs associated with development of expansive soil sites are much higher than those for nonexpansive soil sites. The site investigation and design phase requires more extensive testing and analyses, and the construction phase requires more inspection and attention to detail. Special considerations must be addressed during their occupancy with regard to the maintenance of facilities constructed on expansive soils. Furthermore, the cost to repair the problems caused by expansive soils may be prohibitive. There are many examples where repair costs exceed the original cost of construction.

The nature of expansive soils and the magnitude of costs associated with shortcomings in design, construction, and operation are such that there exists little margin for error in any phase of a project. In that regard, the following quote is appropriate (Krazynski 1979):

To come even remotely close to a satisfactory situation, trained and experienced professional geotechnical engineers must be retained to evaluate soil conditions. The simple truth is that it costs more to build on expansive soils and part of the cost is for the professional skill and judgment needed. Experience also clearly indicates that the cost of repairs is very much higher than the cost of a proper initial design, and the results are much less satisfactory.

In the initial phases of a project, the owner or developer is faced with costs that may be significantly higher than initially estimated. They generally are intolerant of shortcomings and demand that the foundations be designed and constructed such that the movements are within tolerable limits. At the same time, they are reluctant to undertake the required additional cost for something that exists below ground and cannot be seen. One large foundation contractor, Hayward Baker, has as part of its motto, “You never see our best work.” An important task of the engineer is to convince the client that the additional cost is not merely justified, but is critical. This is especially true for critical structures such as hospitals and public buildings, where failure could have serious consequences.

Expansive soils problems exist on every continent, with the exception perhaps of Antarctica. Expansive soils have been encountered in almost every state and province of the United States and Canada, but they are more troublesome in the western and southwestern areas because areas of low precipitation often tend to be more problematic.

In spite of the fact that expansive soils have been designated a geologic hazard, public awareness is lacking. Few universities offer formal courses relating to geotechnical applications for expansive soils. There is a shortage of continuing education courses in the subject, and research is limited to a relatively small number of institutions. As a result, few practicing foundation engineers have received formal education in this area. It is intended that this book will provide a service for awareness, education, and technical reference in this important area.

1.1 Purpose

This book is intended to provide the background and principles necessary for the design of foundations for expansive soils. The nature of expansive soil is described from an engineering perspective to develop an appreciation as to how the microscopic and macroscopic aspects of soil interact to affect expansive behavior. Tools that are necessary to use in the practice of expansive soil foundation design are developed in a fashion that can be easily implemented. The application of these tools to the design of foundations is demonstrated.

An important underlying theme of the book is the ability to predict ground heave and structural movement caused by expansive soil. This is a fundamental part of foundation design. Rigorous calculations of slab heave and potential movement of deep foundations should be a part of every design. Several chapters in this book are devoted to that important subject.

1.2 Organization

The organization of this book is designed to first present the fundamental nature of expansive soil and then address the factors that influence expansion. Those tools provide the means for the design of foundations based on the concept of minimizing structural movement. The first eight chapters present the nature of expansive soil and the tools needed to perform the analyses for foundation design. The remaining chapters apply these tools.

Chapter 2 begins with a microscopic view of the molecular structure of the clay particle and the chemistry of the surrounding water. The concept of a clay micelle is introduced and used to explain the nature of expansive soil and the formation of an expansive soil deposit. That concept is extended to show the manner in which macroscopic factors such as density and water content influence the expansion potential. The distribution of expansive soil throughout the world and representative expansive soil profiles are discussed.

Chapter 3 concentrates on the factors of a site investigation for an expansive soil site that may not be included in the investigation of a nonexpansive soil site. Chapter 4 is devoted to a discussion of soil suction and its role in defining the state of stress. Soil suction is an important parameter that relates to negative pore water pressure and is a major factor influencing the behavior of expansive soil. The state of stress and the stress state variables for unsaturated soils are presented in chapter 5. The nature in which they relate to the classical effective stress concept for saturated soil is discussed, and important constitutive relationships for expansive soils are presented.

Chapter 6 is devoted to the oedometer test. This is the principal method for measuring the expansion potential of a soil and is used extensively in predicting heave. The migration of water through soil is presented in chapter 7. Methods of analysis are presented for the determination of water content profiles to be used in computation of heave and the design of foundations. Chapter 8 discusses methods for computing predicted heave. Two basic methods of predicting heave are presented. One method is based on the application of oedometer test results and the other uses measurements of soil suction.

Chapter 9 introduces the design of foundations and other structural elements for expansive soil sites. Shrink-swell of soils is also considered. This chapter presents general considerations for foundation design and discusses those factors that are unique to expansive soils.

One approach to foundation design on expansive soil is to mitigate their effects by treating the soil or by controlling the water content regime around the structure. Methods of accomplishing those measures are presented in chapter 10. Chapters 11 and 12 present methods of design for shallow and deep foundations to accommodate the forces and movement of expansive soils. Centered on those designs is the computation of predicted foundation movement. This is the fundamental parameter that must guide a successful design. A discussion of several foundation repair options is also provided in these chapters to guide the reader to a successful rehabilitation of distressed structures.

A part of the foundation design must consider the floors and slabs and their interaction with foundation elements. This is addressed in chapter 13. The use of slab-on-grade floors is discouraged in lieu of structural floor systems. Consideration is given to the effect of soil heave on exterior flatwork. Again, repair options for slab-on-grade floors are also provided at the end of this chapter.

Finally, chapter 14 addresses lateral loads that are exerted on foundations and retaining walls by expansive soils. Lateral earth pressure from expansive backfill is generally of such a magnitude as to preclude the use of expansive soil as backfill.

The concepts and design methods that are presented in the previous chapters are demonstrated by several examples that are provided to help guide the reader through the calculations. Case studies of actual sites investigated by the authors have been presented as well. The case studies show applications of the principles presented in this book, not just from a study of the failure to properly apply expansive soil theory, but also from a research perspective that has been gained during development of many of the design methods provided herein.

This book presents design methods in both English and SI units. SI units are presented within the parentheses shown immediately after the English units. There are two exceptions to this. Chapter 4 on soil suction uses SI units primarily. Because most of the data that are used in the examples have been collected from projects in the United States, examples and case studies use only English units.

1.3 Terminology

Many of the terms used in geotechnical practice with expansive soils are either new or have been used in different contexts by different engineers around the world. The following definitions and discussion explain the different terms used in this book. It is suggested that the engineering community adopt this terminology.

1. Expansive soil is generally defined as any soil or rock material that has a potential to increase in volume under increasing water content. In some cases, it is necessary to present a quantitative description of expansive soil. In those cases, expansive soil is described in terms of the following parameters: (1) the percent swell that a soil exhib...

Table of contents

• Cover
• Title Page
• Copyright
• Preface
• List of Symbols
• List of Abbreviations
• Chapter 1: Introduction
• Chapter 2: Nature of Expansive Soils
• Chapter 3: Site Investigation
• Chapter 4: Soil Suction
• Chapter 5: State of Stress and Constitutive Relationships
• Chapter 6: Oedometer Testing
• Chapter 7: Water Migration in Expansive Soils
• Chapter 8: Computation of Predicted Heave
• Chapter 9: General Considerations for Foundation and Floor Design
• Chapter 10: Soil Treatment and Moisture Control
• Chapter 11: Design Methods for Shallow Foundations
• Chapter 12: Design Methods for Deep Foundations
• Chapter 13: Floors and Exterior Flatwork
• Chapter 14: Lateral Pressure on Earth Retaining Structures
• Index
• End User License Agreement