Soils can rarely be described as ideally elastic or perfectly plastic and yet simple elastic and plastic models form the basis for the most traditional geotechnical engineering calculations. With the advent of cheap powerful computers the possibility of performing analyses based on more realistic models has become widely available. One of the aims of this book is to describe the basic ingredients of a family of simple elastic-plastic models of soil behaviour and to demonstrate how such models can be used in numerical analyses. Such numerical analyses are often regarded as mysterious black boxes but a proper appreciation of their worth requires an understanding of the numerical models on which they are based. Though the models on which this book concentrates are simple, understanding of these will indicate the ways in which more sophisticated models will perform.

Soil Behaviour and Critical State Soil Mechanics

Synopsis Within the framework of limit equilibrium methods of stability analysis, no restriction need be placed at the outset upon the shape of the possible slip surface. In many cases, the critical surface may deviate significantly from a circle or a plane and therefore a method that facilitates the analysis of surfaces of arbitrary shape is of interest. A method for doing this is presented. The assumptions necessary to make the problem statically determinate are discussed. The solution of the governing equations ensures that all equilibrium and boundary conditions are satisfied. The method has been programmed for a digital computer and some examples of its application are given. Comparisons are also made with other methods of analysis. Dans la cadre des methodes d'equilibre limite d'analyse de stabilite, il n'y a pas besoin d'imposer de restrictions au depart sur la forme de la surface de glissement eventuelle. Dans bien des cas, la surface critique peut devier d'une maniere significative d'un cercle ou...

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The analysis of the stability of general slip surfaces

The dilatancy and strength of an assembly of individual particles in contact when subjected to a deviatoric stress system is found to depend on the angle of friction $\phi\_\mu$ between the particle surfaces, on the geometrical angle of packing, $\alpha$, and on the degree of energy loss during remoulding. The Mohr-Coulomb criterion of failure which is strictly applicable to a continuum is shown not to have general application to a discontinuous assembly of particles. A theoretical and experimental study of ideal assemblies of rods and uniform spheres establishes expressions for the relation between the rate of dilatancy and the maximum stress ratio for any ideal packing. The solution is extended to the case of a random assembly of irregular particles by investigating the conditions under which the mass dilates such that the rate of internal work absorbed in frictional heat is a minimum. Experiments on random masses of steel, glass, and quartz in which all the physical properties are measured independently show that the minimum energy criterion is closely obeyed by highly dilatant dense over-consolidated and reloaded assemblies throughout deformation to failure. An additional rate of energy has to be supplied to account for losses due to rearranging of loose packings, when the value of $\phi$ to satisfy the theory increases to $\phi\_f$ by an amount dependent on the degree of remoulding. The external stresses applied to an assembly are to be integrated over the $\alpha$-plane defined with reference to figure 14(a) as a plane of repetition of pattern over which the particles interlock, and the resulting forces are to be in equilibrium for sliding on particle interfaces at (45-$\frac{1}{2}\phi_f$) to the direction of the major principal stress. For the special case of no volume change these two planes are identical and the solution agrees then with that based on the Mohr-Coulomb theory. The well-known slip plane in drained discontinuous assemblies is proved to be the result of failure and nothing whatsoever to do with the peak strength. The findings are discussed in the light of previous contributions to the subject.

The stress-dilatancy relation for static equilibrium of an assembly of particles in contact

In the past 25 years great strides have been made in the area of static stability and deformation analysis. The widespread availability of microcomputers has brought about considerable change in the computational aspects of slope stability analysis. Analyses can be done much more thoroughly, and, from the point of view of mechanics, more accurately than was possible without computers. Still, engineers performing slope stability analyses must have more than a computer program. They must have a thorough mastery of soil mechanics and soil strength, a solid understanding of the computer programs they use, and the ability and patience to test and judge the results of their analyses to avoid mistakes and misuse. Realistic analyses of deformations of slopes and embankments were not possible until about 25 years ago. They are possible now mainly because the finite-element method has been developed and adapted to these applications. The principal requirement for achieving reasonably accurate and useful results fro...

State of the Art: Limit Equilibrium and Finite-Element Analysis of Slopes

Soil structure is defined as “the spatial heterogeneity of the different components or properties of soil” Aspects of soil structure which are important for plant development, soil water balance and soil workability are reviewed briefly The different types of soil structure which occur on different size scales are placed in a hierarchical order Different mechanisms give rise to the different hierarchical orders Similarly, different physical/chemical/biological processes are involved in the stabilization of the different hierarchical orders

A number of methods for measuring soil structure are described Preference is given to methods involving direct observation of structural features by scanning electron microscopy and by optical scanning of impregnated sections and fracture surfaces These need to be supported by assessments of the stabilities of compound particles in water and of the mechanical strengths of compound particles as a function of water content

“Good” soil structure is described as one where all the hierarchical orders are well-developed and stable The greatest lack of knowledge appears to be in the 2–100 μm size range which is too large to have been studied by colloid chemists and too small to be visible to the naked eye It is suggested that more observations of soil structure should be made in this size range, as it may hold many important clues on how to manage soil structure in the field

Advances in characterization of soil structure

The use of the Slip Circle in the Stability Analysis of Slopes

Measurement of Soil Properties in the Triaxial Test

THE STRENGTH OF SOILS IS STUDIED IN RELATION TO ' /1/ THE FAILURE CRITERIA WHICH ARE USED TO EXPRESS THE RESULTS OF STRENGTH TESTS AND WHICH REFLECT THE INFLUENCE, IF ANY, OF THE INTERMEDIATE PRINCIPAL STRESS, /2/ THE BEHAVIOR OF SOILS UNDER THE HIGH STRESSES IMPLIED BY THE GREATLY INCREASED HEIGHT OF EARTH AND ROCKFILL DAMS UNDER CONSTRUCTION, /3/ THE DIFFICULTY OF DETERMINING WHAT IS THE IN-SITU UNDRAINED STRENGTH OF A SOIL, DUE TO THE INFLUENCE BOTH OF ANISTROPY AND OF UNREPRESENTATIVE SAMPLING, AND /4/ THE INFLUENCE OF TIME ON THE DRAINED STRENGTH OF SOILS.

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The Strength of Soils as Engineering Materials

Synopsis The application of the effective stress analysis to earth slopes has suffered through lack of a general solution such as that presented by Taylor (1937) for the total stress analysis. Recent developments in computing technique have been applied to the slip circle method and have made it possible to present the results of the effective stress analysis in terms of stability coeffcients from which the factor of safety can be rapidly obtained. Illustrations are given of the use of these coefficients with the distributions of pore pressure encountered in typical earth dams and cuts. L'application de principe des tensions efficace sur l'analyse des pentes de terre c'est empecher de l'absence d'une solution generale, telle que celle du Taylor (1937) pour l'analyse des pentes en termes des tensions totales. L'application des progres recents dans la technique de computation, a la methode du cercle de glissement, a rendu possible la presentation des resultats en termes de coef-ficients de stabilitte, baser...

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Stability Coefficients for Earth Slopes

Synopsis Tests have been carried out on a cohesionless soil to examine the influence of boundary restraint on the observed strength and on the relationships between stress, strain and volume change. To eliminate extraneous errors the axial load in the triaxial compression test has been measured by means of a sensitive proving ring situated within the cell. The proving ring has been calibrated from time to time during the series of tests by a hydraulic system operated by the same dead-weight pressure gauge tester as was used to calibrate the gauge measuring the fluid pressure in the cell. Cylindrical compression tests have been carried out with unlubricated plattens and with one or more layers of rubber membrane lubricated with silicone grease interposed between the ends of the sample and the loading plattens. Samples with three different ratios of height to diameter have been tested. The results indicate that, for the material tested, the effect of end restraint is to increase the apparent strength of the...

Alan W. Bishop

Papers

The use of the Slip Circle in the Stability Analysis of Slopes

Measurement of Soil Properties in the Triaxial Test

The Strength of Soils as Engineering Materials

Stability Coefficients for Earth Slopes

The Influence of End Restraint on the Compression Strength of a Cohesionless Soil