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1983 | Buch | 3. Auflage

Basic Characteristics of Soils Kapitel lesen Erstes Kapitel lesen

Soil Mechanics

verfasst von: R. F. Craig

Verlag: Springer US

Enthalten in: Professional Book Archive

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Über dieses Buch

This book is intended primarily to serve the needs of the undergraduate civil engineering student and aims at the clear explanation, in adequate depth, of the fundamental principles of soil mechanics. The understanding of these principles is considered to be an essential foundation upon which future practical experience in soils engineering can be built. The choice of material involves an element of personal opinion but the contents of this book should cover the requirements of most undergraduate courses to honours level. It is assumed that the student has no prior knowledge of the subject but has a good understanding of basic mechanics. The book includes a comprehensive range of worked examples and problems set for solution by the student to consolidate understanding of the fundamental principles and illustrate their application in simple practical situations. The International System of Units is used throughout the book. A list of references is included at the end of each chapter as an aid to the more advanced study of any particular topic. It is intended also that the book will serve as a useful source of reference for the practising engineer. In the third edition no changes have been made to the aims of the book. Except for the order of two chapters being interchanged and for minor changes in the order of material in the chapter on consolidation theory, the basic structure of the book is unaltered.

Inhaltsverzeichnis

Frontmatter
Chapter 1. Basic Characteristics of Soils
Abstract
To the civil engineer, soil is any uncemented or weakly cemented accumulation of mineral particles formed by the weathering of rocks, the void space between the particles containing water and/or air. Weak cementation can be due to carbonates or oxides precipitated between the particles or due to organic matter. If the products of weathering remain at their original location they constitute a residual soil. If the products are transported and deposited in a different location they constitute a transported soil, the agents of transportation being gravity, wind, water and glaciers. During transportation the size and shape of particles can undergo change and the particles can be sorted into size ranges.
R. F. Craig
Chapter 2. Seepage
Abstract
All soils are permeable materials, water being free to flow through the interconnected pores between the solid particles. The pressure of the pore water is measured relative to atmospheric pressure and the level at which the pressure is atmospheric (i.e. zero) is defined as the water table (WT) or the phreatic surface. Below the water table the soil is assumed to be fully saturated although it is likely that, due to the presence of small volumes of entrapped air, the degree of saturation will be marginally below 100%. The level of the water table changes according to climatic conditions but the level can change also as a consequence of constructional operations. A perched water table can occur locally, contained by soil of low permeability, above the normal water table level. Artesian conditions can exist if an inclined soil layer of high permeability is confined locally by an overlying layer of low permeability: the pressure in the artesian layer is governed not by the local water table level but by a higher water table level at a distant location where the layer is unconfined.
R. F. Craig
Chapter 3. Effective Stress
Abstract
A soil can be visualized as a skeleton of solid particles enclosing continuous voids which contain water and/or air. For the range of stresses usually encountered in practice the individual solid particles and water can be considered incompressible: air, on the other hand, is highly compressible. The volume of the soil skeleton as a whole can change due to rearrangement of the soil particles into new positions, mainly by rolling and sliding, with a corresponding change in the forces acting between particles. The actual compressibility of the soil skeleton will depend on the structural arrangement of the solid particles. In a fully saturated soil, since water is considered to be incompressible, a reduction in volume is possible only if some of the water can escape from the voids. In a dry or a partially saturated soil a reduction in volume is always possible due to compression of the air in the voids, provided there is scope for particle rearrangement.
R. F. Craig
Chapter 4. Shear Strength
Abstract
This chapter is concerned with the resistance of a soil to failure in shear. A knowledge of shear strength is required in the solution of problems concerning the stability of soil masses. If at a point on any plane within a soil mass the shear stress becomes equal to the shear strength of the soil, failure will occur at that point.
R. F. Craig
5. Stresses and Displacements
Abstract
The stresses and displacements in a soil mass due to applied loading are considered in this chapter. Many problems can be treated by analysis in two dimensions, i.e. only the stresses and displacements in a single plane need to be considered. The total normal stresses and shear stresses in the x and z directions on an element of soil are shown in Fig. 5.1, the stresses being positive as shown: the stresses vary across the element.
R. F. Craig
Chapter 6. Lateral Earth Pressure
Abstract
This chapter deals with the magnitude and distribution of lateral pressure between a soil mass and an adjoining retaining structure. Conditions of plane strain are assumed, i.e. strains in the longitudinal direction of the structure are assumed to be zero. The rigorous treatment of this type of problem, with both stresses and displacements being considered, would involve a knowledge of appropriate equations defining the stress-strain relationship for the soil and the solution of the equations of equilibrium and compatibility for the given boundary conditions. The rigorous analysis of earth pressure problems is rarely possible. However, it is the failure condition of the retained soil mass which is of primary interest and in this context, provided a consideration of displacements is not required, it is possible to use the concept of plastic collapse. Earth pressure problems can thus be considered as problems in plasticity.
R. F. Craig
Chapter 7. Consolidation Theory
Abstract
As explained in Chapter 3, consolidation is the gradual reduction in volume of a fully saturated soil of low permeability due to drainage of some of the pore water, the process continuing until the excess pore water pressure set up by an increase in total stress has completely dissipated: the simplest case is that of one-dimensional consolidation, in which a condition of zero lateral strain is implicit. The process of swelling, the reverse of consolidation, is the gradual increase in volume of a soil under negative excess pore water pressure.
R. F. Craig
Chapter 8. Bearing Capacity
Abstract
This chapter is concerned with the bearing capacity of soils on which foundations are supported, a foundation being that part of a structure which transmits loads directly to the underlying soil. If the soil near the surface is capable of adequately supporting the structural loads it is possible to use either footings or a raft. A footing is a relatively small slab giving separate support to part of the structure. A footing supporting a single column is referred to as an individual footing (or pad), one supporting a group of columns as a combined footing and one supporting a load-bearing wall as a strip footing. A raft is a relatively large single slab, usually stiffened, supporting the structure as a whole. If the soil near the surface is incapable of adequately supporting the structural loads, piles or piers are used to transmit the loads to suitable soil (or rock) at greater depth. Foundation level should be below the depth which is subjected to frost action (around 0•5 m in the United Kingdom) and, where appropriate, the depth to which seasonal swelling and shrinkage of the soil takes place.
R. F. Craig
Chapter 9. Stability of Slopes
Abstract
Gravitational and seepage forces tend to cause instability in natural slopes, in slopes formed by excavation and in the slopes of embankments and earth dams. The most important types of slope failure are illustrated in Fig. 9.1. In rotational slips the shape of the failure surface in section may be a circular arc or a non-circular curve. In general, circular slips are associated with homogeneous soil conditions and non-circular slips with non-homogeneous conditions. Translational and compound slips occur where the form of the failure surface is influenced by the presence of an adjacent stratum of significantly different strength. Translational slips tend to occur where the adjacent stratum is at a relatively shallow depth below the surface of the slope: the failure surface tends to be plane and roughly parallel to the slope. Compound slips usually occur where the adjacent stratum is at greater depth, the failure surface consisting of curved and plane sections.
R. F. Craig
Chapter 10. Ground Investigation
Abstract
An adequate ground investigation is an essential preliminary to the execution of a civil engineering project. Sufficient information must be obtained to enable a safe and economic design to be made and to avoid any difficulties during construction. The principal objects of the investigation are: (1) to determine the sequence, thicknesses and lateral extent of the soil strata and, where appropriate, the level of bedrock; (2) to obtain representative samples of the soils (and rock) for identification and classification and, if necessary, for use in laboratory tests to determine relevant soil parameters; (3) to identify the groundwater conditions. The investigation may also include the performance of in-situ tests to assess appropriate soil characteristics. The results of a ground investigation should provide adequate information, for example, to enable the most suitable type of foundation for a proposed structure to be selected and to indicate if special problems are likely to arise during excavation.
R. F. Craig
Backmatter
Metadaten
Titel
Soil Mechanics
verfasst von
R. F. Craig
Copyright-Jahr
1983
Verlag
Springer US
Electronic ISBN
978-1-4899-3474-1
Print ISBN
978-0-442-31434-7
DOI
https://doi.org/10.1007/978-1-4899-3474-1