Soil Mechanics in the Light of Critical State Theories

J.A.R. Ortigao

• Publisher: CRC Press
• Year: 2020
• eBook ISBN:
  9781000150414
• Topic: Physical Sciences
• Subtopic: Agronomy

This work reviews soil mechanics in the light of critical state soil mechanics. A number of exercises are provided, and a microcomputer program, "Cris", used for simulation of the behaviour of soil samples subjected to triaxial tests through the critical state models, accompanies the text.

Chapter 1

Introduction to soil engineering

Introduction

The word soil has to be defined according to its application. For an agronomist, for instance, it is the material that fixes the roots to the ground, and can also be seen as a warehouse from where plants extract nutrients and water. For a mining engineer, the soil overlying an ore pit is simply waste material to be excavated. For a civil engineer, soil is a particle conglomerate from the weathering of rocks, which can easily be excavated and utilized for construction materials or for the support of structures.

As construction or foundation materials, soils are very important for Civil Engineers. In earth dams or in foundations, soils — as concrete or steel bars — are subject to normal and shear stresses and deformation, which ultimately may lead to failure.

Purpose of the book

This book intends to be an introduction to critical state models that enable the calculation of the deformation of a soil element for a given state of stress. These models were developed at the University of Cambridge, England, in the late sixties, and since then have gained widespread use for their simplicity and potential.

The first book on these models was authored by Schofield and Wroth in 1968, being followed by Atkinson and Bransby (1978) and Bolton (1979).

At the Federal University of Rio de Janeiro our interest was drawn only in the 80’s (Almeida, 1982; Almeida et al., 1987; Ortigao and Almeida, 1988), but only after 1985 did our MSc courses include these models. The importance of the Cambridge models has led to their introduction at the undergraduate level since 1985, however mathematical treatment and deduction of equations have been avoided.

Chapter 1 deals with the origin and formation of soils, index properties, At-terberg limits and grain size analysis. These topics will be presented very briefly. To any reader wishing a more comprehensive coverage I suggest the books by: Hunt (1984), Lambe and Whitman (1979) and Mitchell (1976).

The following two chapters cover total and effective stresses in a soil element and also a review of Continuum Mechanics.

In chapter 4 the effect of loading on the ground is studied. Chapter 5 deals with the steady movement of water in soils. Soil compressibility, settlements and consolidation are presented in chapters 6 and 7. Chapter 8 brings an introduction to soil laboratory tests, which is covered in more detail in chapters 9 to 12 for sands and clays. A few practical applications are studied in chapter 13.

Finally, chapter 14 leads to the calculation of deformation in a soil element through the Cam-clay models. A microcomputer program named Crâ is used, then, to avoid all the tedious calculations and to allow a quick simulation of soil behaviour through the Cambridge models.

Origin and formation of soils

Soil is a product of the weathering of rocks, i.e., the deterioration that takes places during geological time span.

Weathering processes can be qualified as chemical or mechanical. Chemical weathering is related to the several chemical processes, very common in tropical climates, which alter, dissolve and deposit the rock mineral components, transforming them into soil. Mechanical weathering takes place due to a transporting agent such as water or wind, or to the effect of temperature changes. Frequently many weathering processes occur simultaneously.

Soils that remain at the site of their formation are called residual, those that suffer the action of transporting agent are called transported or sedimentary, the latter is applied to water-transported soils.

A typical profile of a residual soil is presented in figure 1.1. At great depth the bedrock keeps its original characteristics and remain sound. As it gets closer to the surface the weathering increases. Overlying be...

Table of contents

• Cover
• Half Title
• Title Page
• Copyright Page
• Table of Contents
• Preface
• About the author
• Symbols
• 1.Introduction to soil engineering
• 2.Stresses and deformation in soils
• 3.Initial stresses in soils
• 4.Stresses and elastic loading
• 5.Soil hydraulics
• 6.Compressibility and settlements
• 7.Consolidation
• 8.Laboratory test types
• 9.Behaviour of sands
• 10.Drained behaviour of clays
• 11.Undrained behaviour of clays
• 12.The ϕu = 0 method and UU tests
• 13.Applications to geotechnical engineering
• 14.Cam-clay
• Appendix 1: S1 units in geotechnics
• Appendix 2: Answers to selected exercises
• References
• Subject index