Craig's Soil Mechanics, Seventh Edition
Craig’s Soil Mechanics
Craig’s Soil MechanicsSeventh editionR.F. CraigFormerlyDepartment of Civil EngineeringUniversity of Dundee UK
First published 1974by E & FN Spon, an imprint of Chapman & HallSecond edition 1978Third edition 1983Fourth edition 1987Fifth edition 1992Sixth edition 1997Seventh edition 200411 New Fetter Lane, London EC4P 4EESimultaneously published in the USA and Canadaby Spon Press29 West 35th Street, New York, NY 10001This edition published in the Taylor & Francis e-Library, 2005.“To purchase your own copy of this or any of Taylor & Francis or Routledge’scollection of thousands of eBooks please go to www.eBookstore.tandf.co.uk.”Spon Press is an imprint of the Taylor & Francis Groupª 1974, 1978, 1983, 1987, 1992, 1997, 2004 R.F. CraigAll rights reserved. No part of this book may be reprinted or reproduced orutilised in any form or by any electronic, mechanical, or other means, now knownor hereafter invented, including photocopying and recording, or in any informationstorage or retrieval system, without permission in writing from the publishers.British Library Cataloguing in Publication DataA catalogue record for this book is availablefrom the British LibraryLibrary of Congress Cataloging in Publication DataCraig, R.F. (Robert F.)[Soil mechanics]Craig’s soil mechanics / R.F. Craig. — 7th ed.p. cm.Second ed.: Soil mechanics / R.F. Craig. Van Nostrand Reinhold, 1978.Includes bibliographical references and index.ISBN 0–415–32702–4 (hb.: alk. paper) — ISBN 0–415–32703–2 (pbk.: alk.paper)1. Soil mechanics. I. Title: Soil mechanics. II. Craig, R.F. (Robert F.) Soilmechanics. III. Title.TA710.C685 2004624.10 5136—dc222003061302ISBN 0-203-49410-5 Master e-book ISBNISBN 0-203-57441-9 (Adobe eReader Format)ISBN 0–415–32702–4 (hbk)ISBN 0–415–32703–2 (pbk)
ContentsPrefaceviii1Basic characteristics of soils1.1The nature of soils1.2Particle size analysis1.3Plasticity of fine soils1.4Soil description and classification1.5Phase relationships1.6Soil .1Soil water2.2Permeability2.3Seepage theory2.4Flow nets2.5Anisotropic soil conditions2.6Non-homogeneous soil conditions2.7Transfer condition2.8Seepage through embankment dams2.9Grouting2.10 Frost Effective stress3.1Introduction3.2The principle of effective stress3.3Response of effective stress to a change in total stress3.4Partially saturated soils3.5Influence of seepage on effective stressProblemsReferences7171717479808890
viContents4 Shear strength4.1Shear failure4.2Shear strength tests4.3Shear strength of sands4.4Shear strength of saturated clays4.5The critical-state concept4.6Residual strength4.7Pore pressure 71331355 Stresses and displacements5.1Elasticity and plasticity5.2Stresses from elastic theory5.3Displacements from elastic theoryProblemsReferences1361361441551591606 Lateral earth pressure6.1Introduction6.2Rankine’s theory of earth pressure6.3Coulomb’s theory of earth pressure6.4Application of earth pressure theory to retaining walls6.5Design of earth-retaining structures6.6Gravity walls6.7Embedded walls6.8Braced excavations6.9Diaphragm walls6.10 Reinforced 152172212257 Consolidation theory7.1Introduction7.2The oedometer test7.3Consolidation settlement: one-dimensionalmethod7.4Settlement by the Skempton–Bjerrum method7.5The stress path method7.6Degree of consolidation7.7Terzaghi’s theory of one-dimensional consolidation7.8Determination of coefficient of consolidation7.9Correction for construction period7.10 Numerical solution7.11 Vertical 2260265268274276
Contentsvii8Bearing capacity8.1Foundation design8.2Ultimate bearing capacity8.3Allowable bearing capacity of clays8.4Allowable bearing capacity of sands8.5Bearing capacity of piles8.6Ground improvement techniques8.7Excavations8.8Ground 393423449Stability of slopes9.1Introduction9.2Analysis for the case of u ¼ 09.3The method of slices9.4Analysis of a plane translational slip9.5General methods of analysis9.6End-of-construction and long-term stability9.7Embankment 7110Ground investigation10.1 Introduction10.2 Methods of investigation10.3 Sampling10.4 Borehole logs10.5 Geophysical methods10.6 Ground ase studies11.1 Introduction11.2 Field instrumentation11.3 The observational method11.4 Illustrative casesReferences395395396407409434Principal symbolsAnswers to problemsIndex436440443
PrefaceThis 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 fundamentalprinciples of soil mechanics. The understanding of these principles is considered to bean essential foundation upon which future practical experience in geotechnical engineering can be built. The choice of material involves an element of personal opinion butthe contents of this book should cover the requirements of most undergraduatecourses to honours level as well as parts of some Masters courses.It is assumed that the reader has no prior knowledge of the subject but has a goodunderstanding of basic mechanics. The book includes a comprehensive range ofworked examples and problems set for solution by the student to consolidate understanding of the fundamental principles and illustrate their application in simplepractical situations. Both the traditional and limit state methods of design are includedand some of the concepts of geotechnical engineering are introduced. The differenttypes of field instrumentation are described and a number of case studies are includedin which the differences between prediction and performance are discussed. Referencesare included as an aid to the more advanced study of any particular topic. It isintended that the book will serve also as a useful source of reference for the practisingengineer.The author wishes to record his thanks to the various publishers, organizations andindividuals who have given permission for the use of figures and tables of data, and toacknowledge his dependence on those authors whose works provided sources ofmaterial. Extracts from BS 8004: 1986 (Code of Practice for Foundations) and BS5930: 1999 (Code of Practice for Site Investigations) are reproduced by permission ofBSI. Complete copies of these codes can be obtained from BSI, Linford Wood, MiltonKeynes, MK14 6LE.Robert F. CraigDundeeMarch 2003
The unit for stress and pressure used in this book is kN/m2 (kilonewton per squaremetre) or, where appropriate, MN/m2 (meganewton per square metre). In SI thespecial name for the unit of stress or pressure is the pascal (Pa) equal to 1 N/m2(newton per square metre). Thus:1 kN/m2 ¼ 1 kPa (kilopascal)1 MN/m2 ¼ 1 MPa (megapascal)
Chapter 1Basic characteristics of soils1.1THE NATURE OF SOILSTo the civil engineer, soil is any uncemented or weakly cemented accumulation ofmineral particles formed by the weathering of rocks, the void space between theparticles containing water and/or air. Weak cementation can be due to carbonatesor oxides precipitated between the particles or due to organic matter. If the productsof weathering remain at their original location they constitute a residual soil. Ifthe products are transported and deposited in a different location they constitutea transported soil, the agents of transportation being gravity, wind, water and glaciers.During transportation the size and shape of particles can undergo change and theparticles can be sorted into size ranges.The destructive process in the formation of soil from rock may be either physical orchemical. The physical process may be erosion by the action of wind, water or glaciers,or disintegration caused by alternate freezing and thawing in cracks in the rock. Theresultant soil particles retain the same composition as that of the parent rock. Particlesof this type are described as being of ‘bulky’ form and their shape can be indicated byterms such as angular, rounded, flat and elongated. The particles occur in a wide rangeof sizes, from boulders down to the fine rock flour formed by the grinding action ofglaciers. The structural arrangement of bulky particles (Figure 1.1) is described assingle grain, each particle being in direct contact with adjoining particles without therebeing any bond between them. The state of the particles can be described as dense,medium dense or loose, depending on how they are packed together.The chemical process results in changes in the mineral form of the parent rock dueto the action of water (especially if it contains traces of acid or alkali), oxygen andcarbon dioxide. Chemical weathering results in the formation of groups of crystallineparticles of colloidal size ( 0:002 mm) known as clay minerals. The clay mineralkaolinite, for example, is formed by the breakdown of feldspar by the action of waterand carbon dioxide. Most clay mineral particles are of ‘plate-like’ form having a highspecific surface (i.e. a high surface area to mass ratio) with the result that theirstructure is influenced significantly by surface forces. Long ‘needle-shaped’ particlescan also occur but are comparatively rare.The basic structural units of most clay minerals are a silicon–oxygen tetrahedronand an aluminium–hydroxyl octahedron, as illustrated in Figure 1.2(a). There arevalency imbalances in both units, resulting in net negative charges. The basicunits, therefore, do not exist in isolation but combine to form sheet structures. The
2Basic characteristics of soilsFigure 1.1 Single grain oxygen tetrahedronSilica sheetAluminium–hydroxyl octahedron(a)(b)Gibbsite sheetFigure 1.2 Clay minerals: basic units.tetrahedral units combine by the sharing of oxygen ions to form a silica sheet. Theoctahedral units combine through shared hydroxyl ions to form a gibbsite sheet. Thesilica sheet retains a net negative charge but the gibbsite sheet is electrically neutral.Silicon and aluminium may be partially replaced by other elements, this being knownas isomorphous substitution, resulting in further charge imbalance. The sheet structures are represented symbolically in Figure 1.2(b). Layer structures then form by thebonding of a silica sheet with either one or two gibbsite sheets. Clay mineral particlesconsist of stacks of these layers, with different forms of bonding between the layers.The structures of the principal clay minerals are represented in Figure 1.3.Kaolinite consists of a structure based on a single sheet of silica combined with asingle sheet of gibbsite. There is very limited isomorphous substitution. The combinedsilica–gibbsite sheets are held together relatively strongly by hydrogen bonding. Akaolinite particle may consist of over 100 stacks. Illite has a basic structure consistingof a sheet of gibbsite between and combined with two sheets of silica. In the silica sheet
The nature of soils3Figure 1.3 Clay minerals: (a) kaolinite, (b) illite and (c) montmorillonite.there is partial substitution of silicon by aluminium. The combined sheets are linkedtogether by relatively weak bonding due to non-exchangeable potassium ions heldbetween them. Montmorillonite has the same basic structure as illite. In the gibbsitesheet there is partial substitution of aluminium by magnesium and iron, and in thesilica sheet there is again partial substitution of silicon by aluminium. The spacebetween the combined sheets is occupied by water molecules and exchangeable cationsother than potassium, resulting in a very weak bond. Considerable swelling of montmorillonite can occur due to additional water being adsorbed between the combinedsheets.The surfaces of clay mineral particles carry residual negative charges, mainly as aresult of the isomorphous substitution of silicon or aluminium by ions of lower valencybut also due to disassociation of hydroxyl ions. Unsatisfied charges due to ‘brokenbonds’ at the edges of particles also occur. The negative charges result in cationspresent in the water in the void space being attracted to the particles. The cations arenot held strongly and, if the nature of the water changes, can be replaced by othercations, a phenomenon referred to as base exchange.Cations are attracted to a clay mineral particle because of the negatively chargedsurface but at the same time they tend to move away from each other because of theirthermal energy. The net effect is that the cations form a dispersed layer adjacent to theparticle, the cation concentration decreasing with increasing distance from the surfaceuntil the concentration becomes equal to that in the general mass of water in the voidspace of the soil as a whole. The term double layer describes the negatively chargedparticle surface and the dispersed layer of cations. For a given particle the thickness ofthe cation layer depends mainly on the valency and concentration of the cations: anincrease in valency (due to cation exchange) or an increase in concentration will resultin a decrease in layer thickness. Temperature also affects cation layer thickness, anincrease in temperature resulting in a decrease in layer thickness.Layers of water molecules are held around a clay mineral particle by hydrogenbonding and (because water molecules are dipolar) by attraction to the negativelycharged surfaces. In addition the exchangeable cations attract water (i.e. they becomehydrated). The particle is thus surrounded by a layer of adsorbed water. The waternearest to the particle is strongly held and appears to have a high viscosity, but theviscosity decreases with increasing distance from the particle surface to that of ‘free’water at the boundary of the adsorbed layer. Adsorbed water molecules can move
4Basic characteristics of soilsrelatively freely parallel to the particle surface but movement perpendicular to thesurface is restricted.Forces of repulsion and attraction act between adjacent clay mineral particles.Repulsion occurs between the like charges of the double layers, the force of repulsiondepending on the characteristics of the layers. An increase in cation valency orconcentration will result in a decrease in repulsive force and vice versa. Attractionbetween particles is due to short-range van der Waals forces (electrical forces ofattraction between neutral molecules), which are independent of the double-layercharacteristics, that decrease rapidly with increasing distance between particles. Thenet interparticle forces influence the structural form of clay mineral particles ondeposition. If there is net repulsion the particles tend to assume a face-to-face orientation, this being referred to as a dispersed structure. If, on the other hand, there is netattraction the orientation of the particles tends to be edge-to-face or edge-to-edge, thisbeing referred to as a flocculated structure. These structures, involving interactionbetween single clay mineral particles, are illustrated in Figures 1.4(a) and (b).In natural clays, which normally contain a significant proportion of larger, bulkyparticles, the structural arrangement can be extremely complex. Interaction betweensingle clay mineral particles is rare, the tendency being for the formation of elementaryaggregations of particles (also referred to as domains) with a face-to-face orientation. Inturn these elementary aggregations combine to form larger assemblages, the structure ofwhich is influenced by the depositional environment. Two possible forms of particleassemblage, known as the bookhouse and turbostratic structures, are illustrated in Figures1.4(c) and (d). Assemblages can also occur in the form of connectors or a matrix betweenlarger particles. An example of the structure of a natural clay, in diagrammatical form, isshown in Figure 1.4(e). A secondary electron image of Errol Clay is shown in Figure 1.5,the solid bar at the bottom right of the image representing a length of 10 mm.Particle sizes in soils can vary from over 100 mm to less than 0.001 mm. In BritishStandards the size ranges detailed in Figure 1.6 are specified. In Figure 1.6 the terms‘clay’, ‘silt’, etc. are used to describe only the sizes of particles between specified limits.However, the same terms are also used to describe particular types of soil. Most soilsconsist of a graded mixture of particles from two or more size ranges. For example,clay is a type of soil possessing cohesion and plasticity which normally consists ofparticles in both the clay size and silt size ranges. Cohesion is the term used to describethe strength of a clay sample when it is unconfined, being due to negative pressure inFigure 1.4 Clay structures: (a) dispersed, (b) flocculated, (c) bookhouse and (d) turbostratic;(e) example of a natural clay.
The nature of soils5Figure 1.5 Structure of Errol Clay.Figure 1.6 Particle size ranges.the water filling the void space, of very small size, between particles. This strengthwould be lost if the clay were immersed in a body of water. It should be appreciatedthat all clay-size particles are not necessarily clay mineral particles: the finest rock flourparticles may be of clay size. If clay mineral particles are present they usually exert aconsiderable influence on the properties of a soil, an influence out of all proportion totheir percentage by weight in the soil. Soils whose properties are influenced mainly byclay and silt size particles are referred to as fine soils. Those whose properties areinfluenced mainly by sand and gravel size particles are referred to as coarse soils.
6Basic characteristics of soils1.2PARTICLE SIZE ANALYSISThe particle size analysis of a soil sample involves determining the percentage by massof particles within the different size ranges. The particle size distribution of a coarsesoil can be determined by the method of sieving. The soil sample is passed through aseries of standard test sieves having successively smaller mesh sizes. The mass of soilretained in each sieve is determined and the cumulative percentage by mass passingeach sieve is calculated. If fine particles are present in the soil, the sample should betreated with a deflocculating agent and washed through the sieves.The particle size distribution of a fine soil or the fine fraction of a coarse soil can bedetermined by the method of sedimentation. This method is based on Stokes’ lawwhich governs the velocity at which spherical particles settle in a suspension: the largerthe particles the greater is the settling velocity and vice versa. The law does not applyto particles smaller than 0.0002 mm, the settlement of which is influenced by Brownianmovement. The size of a particle is given as the diameter of a sphere which would settleat the same velocity as the particle. Initially the soil sample is pretreated with hydrogenperoxide to remove any organic material. The sample is then made up as a suspensionin distilled water to which a deflocculating agent has been added to ensure that allparticles settle individually. The suspension is placed in a sedimentation tube. FromStokes’ law it is possible to calculate the time, t, for particles of a certain ‘size’, D (theequivalent settling diameter), to settle to a specified depth in the suspension. If, afterthe calculated time t, a sample of the suspension is drawn off with a pipette at thespecified depth below the surface, the sample will contain only particles smaller thanthe size D at a concentration unchanged from that at the start of sedimentation. Ifpipette samples are taken at the specified depth at times corresponding to other chosenparticle sizes the particle size distribution can be determined from the masses of theresidues. An alternative procedure to pipette sampling is the measurement of thespecific gravity of the su
Title: Soil mechanics. II. Craig, R.F. (Robert F.) Soil mechanics. III. Title. TA710.C685 2004 624.105136—dc22 2003061302 ISBN 0–415–32702–4 (hbk) ISBN 0–415–32703–2 (pbk) This edition published in the Taylor & Francis e-Library, 2005. ISBN 0-203-49410-5 Master e-book ISBN
3 Objectives of Soil Mechanics To perform the Engineering soil surveys. To develop rational soil sampling devices and soil sampling methods. To develop suitable soil testing devices and soil testing methods. To collect and classify soils and their physical properties on the basis of fundamental knowledge of soil mechanics. To investigate the physical properties of soil and
M.E. SOIL MECHANICS AND FOUNDATION ENGINEERING SEMESTER I SL. NO. COURSE CODE COURSE TITLE L T P C THEORY 1 MA9103 Applied Mathematics 3 1 0 4 2 SF9101 Theoretical Soil Mechanics 4 0 0 4 3 SF9102 Strength and Deformation Behaviour of Soils 3 0 0 3 . Graham Barnes, Soil Mechanics Principles and Practices, Macmillan Press
2. Intermediate Mechanics of Materials (2001) J.R BARBER 4(12) 3. Mechanics of Materials (2002) Madhukar Vable 9(11) 4. Mechanics of Materials (Fifth Edition) Ferdinand P. Be er, E. Russell Johnston, Jr. 7(11) 5. Mechanics of Materials (Seventh Edition) R.C.Hibbeler 9(14) 6. Mechanics of Mat
Mechanics and Mechanics of deformable solids. The mechanics of deformable solids which is branch of applied mechanics is known by several names i.e. strength of materials, mechanics of materials etc. Mechanics of rigid bodies: The mechanics of rigid bodies is primarily concerned with the static and dynamic
Soil Map Units A soil map unit is a collection of areas defined and named the same in terms of their soil components (e.g., series) or miscellaneous areas or both –Fallsington sandy loam, 0 to 2% slopes –Marr-Dodon complex, 2 to 5% slopes Soil map units are the basic unit of a soil map Each soil map unit differs in some
hydraulic energy to shear and blend the soil in situ, creat-ing a soil cement mix of the highest quality. Our high en-ergy jet mixing system has allowed us to extend soil mix-ing to stiff, highly plastic clays and weathered rock, soils SOIL MIXING TECHNOLOGY — SINGLE AXIS Benefits of Deep Soil Mixing Efficient and cost effective method
CRAIG SINGS WITH CRAIG CRAIG DOUGLAS is the latest to try the self -duetting trick on records. His latest, I'm So Glad I Found Her, has Craig singing along with himself a third apart. The disc is on Decca Ritz, coupled with Love Her While She's Young-which Craig des-cribes as: "a pretty ba
Organist) and a fine choir, affiliated to the RSCM. Young singers train through the RSCM Voice for Life scheme, at which they have achieved much success in recent years. At present we have 17 trebles (both boys and girls) of school age and 19 adults. Funding is available for organ and choral scholars. The choir sings: at the 9:15 Parish Eucharist every Sunday during term time Choral .
