Showing papers in "Geotechnique in 1970"

The influence of strains in soil mechanics

Abstract: Synopsis The aims, during the past 20 years, of the Cambridge research programme in soil mechanics are outlined. The principal objective is to develop an understanding of the stress–strain behaviour of soils so that reliable predictions can be made concerning their load-deformation characteristics at all working loads, rather than only loads at failure, in practical problems. A superstructure and its foundation can then be designed as a unit. The pressing need for the study of the load-deformation behaviour of soils in mixed boundary value problems at model scale is emphasized. New versatile shear test equipment which can impose a wide range of stress and/or strain paths, together with non-destructive methods of checking the uniformity of the behaviour of specimens, are briefly described. Typical data are presented for one problem, illustrating the variation of the passive pressure on a retaining wall with the displacement of that wall into sand. A revised statement of the Mohr-Coulomb failure criterion i...

Experimental Determination of the Shape Factors and the Bearing Capacity Factors of Sand

Abstract: Synopsis In order to determine the values of the shape factors to be introduced in the formula of ultimate bearing capacity of shallow foundations, an extensive series of tests on small footings resting on fine sand was performed at Ghent. To obtain a homogeneous and given density the sand was placed in a fully automatic way, under control of the output and the height of fall of the sand. To eliminate the depth effect the overburden pressure was realized by air pressure in inflated rubber bags covering the surface of the sand. From the tests formulae for the shape factors sq, sc and sγ are deduced. It appears that the shape factor sγ in the weight term is independent of the angle of friction, while the shape factors sq and sc are not. In the formulae given for s and sc the influence of the state of strain is implicitly included; however, different formulae are given depending on whether the effect of the curvature of the intrinsic curve on the introduced shear strength parameters has been considered or no...

First-Time Slides in Over-Consolidated Clays

Abstract: (a) After a slide has taken place the strength on the slip surface is equal to the residual value. The residual strength is associated with strong reorientation of the clay particles and is represented by an angle of shearing resistance $= which in most clays is considerably smaller than the value of 4’ at peak strength (Fig. 1). (b) First-time slides in slopes in non-fissured clays correspond to strengths only slightly less than the peak. (c) First-time slides in fissured clays correspond to strengths well below the peak. (d) Some form of progressive failure must be operative to take the clay past the peak. This could be simply the result of a non-uniform ratio of stress to strength along the potential slip surface; but probably the fissures play an important role as stress concentrators and in leading to softening of the clay mass. (e) Granted a progressive failure mechanism the limiting strength would be residual, and it is therefore reasonable to express the actual strength at the time of failure as a function of the upper (peak) and lower (residual) limits, i.e. by the residual factor. (f) In natural slopes of London CIay the strength has fallen approximateIy to the residual value. (g) The residual strength obtains on pre-existing shear surfaces, whether these are the result of tectonic shearing or old landslides.

The Role of Waves in Causing Submarine Landslides

Abstract: Synopsis The effects of ocean waves on the stability of underwater slopes in soft underconsolidated deltaic sediments are examined. The pressure changes on the sea floor, associated with the passage of a wave, are able to cause shear failure in soft sediments in water depths up to about 400 ft. The waves impose an oscillatory motion on the soft sediments which, on sloping ground, leads to a mass transfer of soil down slope. Also the repeated reversals of shear strain in the sediment cause remoulding of the sediment and a reduction in shear strength. Les effets des vagues de I'ocean sur la stabilite des pentes sous-marines dans des sediments deltaiques sous consolides mous sont examines. Les changements de pression sur les fonds des mers, qui s'associent au passage d'une vague, sont capables de provoquer une rupture par cisaillement dans des sediments mous dans des profondeurs d'eau allant jusqu' a 130 m. Les vagues imposent un mouvement oscillatoire aux sediments mous qui, sur un sol en pente, entraine un...

Anisotropic elastic parameters for soil

Abstract: Synopsis The concept of soil as an anisotropic elastic material is considered and the theoretical bounding values of the relevant elastic parameters are described. The bounding values of the parameters are repre-sented in three-dimensional space. Within the space any given material is represented by a point and points in certain regions represent particular types of material. The requirements for infinite bulk modulus, for uncoupled volumetric and distortional phenomena and for dilatant soil are repre-sented within the bounds of possible materials. On considere le concept du sol en tant que materiau eĺastique anisotrope et on decrit les valeurs limites theoriques des parametres d'elasticite s'y rapportant. Les valeurs limites des parametres sont repre-sentEes dans un espace a trois dimensions. A l'interieur de l'espace, tout materiau donne est represente par un point et des points dans certaines zones representent des types particuliers de materiaux. Les conditions requises pour un module de masse infinie...

The Relationship Between the Shear Strength of Sands in Triaxial Compression, Plane Strain and Direct Shear

Abstract: Synopsis A theoretical relation is derived between the peak Coulomb φ values for saturated drained sands measured in the direct shear test and the plane strain compression test using the stress-dilatancy equation and the assumption that the directions of principal strain increment and principal stress coincide. Limiting dilatancy rates in triaxial compression allow an overall comparison of the φ values to be expected in these three types of test. Present available experimental data indicate quite close agreement over the range φu = 17°–39° for cohesion-less soils. On derive une relation theorique entre les valeurs φ de pointe de Coulomb pour des sables draines satures mesurees dans l'essai de cisaillement direct et l'essai de compression a deformation en plan en utilisant 1'equation de contrainte-dilatabilite et la supposition que les directions de l'accroissement de deformation principale et de la contrainte principale coincident. Des taux limites de dilatabilite en compression tr axiale permettent de fa...

Ignition Loss and other Properties of Peats and Clays from Avonmouth, King's Lynn and Cranberry Moss

Abstract: Synopsis Ignition loss, liquid limit and specific gravity have been measured on 28 samples of peats and clays from the coastal flats near Avonmouth, from the Fens near King's Lynn and from Cranberr...

Experimental and theoretical investigations of a passive earth pressure problem

Abstract: Synopsis The Paper presents data from the experimental investigation of the passive failure of an initially vertical, rough, plane wall which is rotated about its toe into a mass of dry sand with an unloaded horizontal surface. The sand is constrained to deform in plane strain. Measurements are made of the distribution of the normal and shear stresses on the wall while strain fields are determined from observations by an X-ray technique of the positions of lead shot buried in the sand mass. The form of the rupture surface mechanism in dense sand is determined. The strain data are used to investigate the φ= constant assumption of the Sokolovski (1965) method and Sokolovski solutions are compared with the experimental data for two cases. There is marked agreement between the predicted principal compressive stress directions and the observed principal compressive strain increment directions. Cet Expose presente des donnees provenant de recherches experimentales portant sur la rupture de butee d'un mur plan, ...

Shear Strength of Montmorillonite

Abstract: Synopsis Artificially sedimented specimens of Wyoming bentonite (Volclay) were used to investigate the effect of physico–chemical variables on the shear strength properties of montmorillonite. Triaxial compression tests were performed on calcium and sodium montmorillonite at various electrolyte concentrations. The influence of the type of adsorbed cation and concentration of electrolyte in the free pore water on the shear strength of montmorillonite was investigated using undrained triaxial compression tests with pore water pressure measurements. The effective-stress failure envelopes of calcium and sodium montmorillonite were curved: in the range of stress studied their slopes decreased from 15° to 10° and 4° to 0°. for calcium and sodium montmorillonite respectively. The decrease in slope of the effective-stress failure envelope could be due to greater parallelism of clay plates at higher consolidation pressures. A series of drained triaxial compression tests using calcium montmorillonite yielded the sa...

A Coastal Mudflow on the London Clay Cliffs at Beltinge, North Kent

Abstract: Synopsis The Paper describes an investigation into the nature and movements of a coastal mudflow on London Clay cliffs at Beltinge, north Kent, which are undergoing moderate marine erosion The mud

Fully Developed Plastic Shear Flow of Granular Materials

Abstract: Synopsis A consistent mechanical basis is presented for the mathematical description of plane, plastic shear deformation of frictional, cohesive or cohesionless granular materials The deformation considered is fully developed flow of particles which override each other over long distances It is an idealization of the cataclastic flow by which all faulting processes in loose or slightly consolidated sediments proceed It is shown that granular material in fully developed shear flow exhibits all the essential properties of a perfectly plastic material In particular, it lacks a one-to-one correspondence between strain rates and stresses, as is explained by a discussion of the energy dissipation involved Instead the relation between stress and strain increments reduces to a relation between corresponding principal directions of the two tensors Despite the plastic character of the flow, the flow rules obtained by employing the rheological concept of perfect plasticity to granular materials (perfect soil p

Electrochemical Hardening of Clay Soils

Abstract: Synopsis Clay soils were strengthened by introducing aluminium into the soil under an electrochemical gradient. Changes in both the composition and physical properties of the treated soils were investigated. The role of pH and pH buffering during treatment was also examined. Strength increases or decreases in the treated samples were separated into three components: those caused by a change in water content, electroosmotic effects; those caused by age hardening, thixotropic effects; and those caused by electrochemical action, ion exchange and mineralization. Nearly all treated samples exhibited some degree of electrochemical hardening. Induration was most pronounced in ahigh water content, high pH, bentonitic soil due largely to hydroxy–aluminium interlayering in the clay. In a low pH. illitic soil interlayering was negligible and hardening appears to have resulted primarily from ion exchange. Both X-ray diffraction and selective extraction methods were used to determinethe distribution and mode of occurr...

Stress-Probe Experiments on Saturated Normally Consolidated Clay

Abstract: Synopsis Rendulic's (1937) investigation of a unique relationship between effective stresses and void ratio for saturated remoulded clays was limited to the case where the loading was being increased. During unloading a different relationship between effective stresses and void ratio operates, and Roscoe and Schofield (1963) have suggested that this could be accounted for in terms of elastic behaviour. The evidence offered in support of these concepts has so far relied mainly on conventional drained and nndrained triaxial tests. The Paper describes stress-controlled triaxial tests on a remoulded, saturated, powdered slate dust. The samples were anisotropically consolidated and then stress-probed in all directions of loading and unloading within the triaxial plane. The results distinguish between the forms of behaviour for loading and unloading, and there is general agreement with the volume changes predicted according to the concepts of Rendulic and of Roscoe and Schofield. It is shown that using the norm...

A Stero-Photogrammetric Method for Measuring Displacement Fields

Abstract: Synopsis A new whole field displacement measuring technique is described which is suitable for measuring planar displacements of any textured plane surface. The method uses ordinary photographs, taken from a fixed camera position, and a development of normal stereo-photogrammetric contouring procedures. Displacement measurements of the order of O·01 mm are possible on the photographic plates used for plotting. The technique is described in detail and illustrated with displacement contours obtained from a sand model deforming in plane strain. Une nouvelle technique de mesure du deplacement d'un champ entier est decrite qui convient a la mesure des deplacements planaires de toute sur-face plane presentant une certaine structure. La methode utilise des photographies ordinaires, prises par un appareil place a une position fixe, et le developpement des procedes normaux des profils stereophotogrammetriques. Des mesures de deplacements de l'ordre de 0,Ol mm sont possibles sur les plaques photographiques utilisee...

The Operational Strength of Fissured Clays

Abstract: Synopsis In clays that are generally, but not necessarily, stiff fissures or joints exist with varying intensity. As the shear strengths along these discontinuities are much less than those of the intact material, they constitute planes of weakness, with the result that the strength measured depends on the size of the sample used. Previous theories on the strength–size relation are reviewed and their limitations discussed. An equation is proposed to describe this behaviour and a method of determining the parameters involved in the equation is developed. The results of field and laboratory tests on block samples of a stiff fissured clay, and data reported in the literature, were analysed. It was shown that the strength–size relation may be represented adequately by the proposed equation and that the strength of the clay mass operative in the field may be predicted. By taking the effect of sample size, anisotropy and time to failure into account, the conventional φ= 0 analysis, hitherto considered unreliabl...

Soil deformation rates and activation energies

Abstract: Synopsis The viscous flow of dilute soil–water mixtures and the steady state creep of consolidated soil samples were studied in the determination of the free energy of activation by application of the absolute reaction rate theory. The Sault St Marie clay used was treated to remove carbonates and then divided into three batches which were saturated with lithium, sodium or potassium ions. Portions of these samples were dehydrated and then saturated with non-polar carbon tetrachloride. The viscosity of the soil–water mixtures was a function of the concentration of solids and the nature of the adsorbed ions. The highly hydrated lithium ion caused the more rapid increase in viscosity because of the larger effective size. The free energy of activation of the dilute soil suspensions was independent of solids' concentration and equal to that of pure water. The flow mechanism was that of free water and the isolated clay particles made no contribution to the free energy. Creep tests on consolidated clay samples co...

Overconsolidation in Soft Clay Deposits

Abstract: A METHOD OF SEPARATING THE DEGREE OF OVERCONSOLIDATION OF SOFT CLAY DEPOSITS, WHICH RESULT FROM CHANGES IN GROUND STRESSES AND GROUNDWATER LEVEL AND FROM TOTAL DEGREE OF OVERCONSOLIDATION IN THE GROUND, IS OUTLINED. /RRL/

Some loading tests on long pipe piles

Abstract: Synopsis Two steel pipe piles of 24 in. dia. were driven, one into granular and the other into cohesive soil, and test loaded in such a manner as to measure separately the skin friction and end-bearing components of the pile capacity. The Paper describes the tests and presents the pertinent geotechnical properties of the subsoil at each test pile. The values of skin friction and end-bearing so determined are reported. The pile driven into the cohesive soil was test loaded at various times after driving to determine any change in pile capacity with time. A feature of the site was the presence of artesian water pressures in the soil. The computed and measured values of pile capacity are compared. The skin friction and end-bearing values determined in the tests are used to estimate the bearing capacity of 60 in. dia. steel pipe piles to be driven at the site. Deux pieux en tuyaux d'acier de 609,6 mm de diametre furent enfonces, l'un dans un sol granulaire et l'autre dans un sol coherent, et furent soumis a d...

An extension to the theory of the constant head in situ permeability test

Abstract: Synopsis The theory of the in situ constant head permeability test (Gibson, 1963) is shown to be strictly valid only if the soil behaves as a porous perfectly elastic medium. For this ideal soil th...

A Shallow Slab Slide in the Lias Clay Near Uppingham, Rutland

Abstract: Synopsis The landslide is shown to result from movement on an extensive pre-existing shear surface in a 9° Lias clay slope. The slide is of particular interest since the slope angle was close to the observed angle of ultimate stability against land-sliding for the Lias clay in the East Midlands. It follows that this slide provides a test case to check the supposition that, other factors being equal, the lowest angle of unstable slope occurs when the ground water table coincides with ground level. The slide occurred in about 1962; piezometers installed shortly after a further small movement in the winter of 1968–9 showed the phreatic surface to be virtually at the ground surface. Stability analyses indicate that the movement was highly consistent both with the observed pore water pressures and the shear strength parameters of the slip surface. On fait apparaitre que le glissement de terrain resulte d'un deplacement se produisant sur une surface de cisaillement etendue existant au prealable sur une pente d'...

Incremental Numerical Solution of a Simple Deformation Problem in Soil Mechanics

Abstract: Synopsis During the past decade advances in the techniques of laboratory testing of soil materials have led to the development of constitutive theories which are perhaps lacking in generality and liable to modification as further experimental evidence comes to light. However, in principle they make possible the solution of some boundary value problems for soils throughout the range of deformations up to collapse. Concurrently computer-orientated methods of stress analysis have progressed to the point where the inherently non-linear, state dependent behaviour of soil continua can be treated on a step-by-step basis. This Paper brings together these two advances, in that the displacement finite element computation method is used to solve the boundary value problem of plane strain expansion of thick-walled hollow cylinders of soil. Drained cohesionless materials are assumed to deform consistently with the stress-dilatancy flow concept, and fully drained clays consistently with the Cam clay flow model. The pre...

Stresses and Displacements in an Elastic Layer due to Inclined and Eccentric Load Over a Rigid Strip

Abstract: Synopsis Using the finite element method, a set of influence factors for the stresses in, and the surface displacements of, an elastic layer of finite thickness have been obtained. Stresses and displacements due to inclined and eccentric load over a rigid strip have been calculated for the ratio H/B=1·0, 2·0 and 3·0, where H is the thickness of the compressible layer and B is the width of the rigid strip foundation, and for Poisson's ratio μ=0·005, 0·30 and 0·45. The values of the stress and displacement coefficients are given in tabular form and some of them are also presented graphically En utilisant la methode des elements finis, des facteurs d'influence pour le calcul des contraintes a l'interieur du milieu et des deplacements a la surface sont obtenus dans le cas d'une couche elastique d'epaisseur finie. Les contraintes et les deplacements produits par une force inclinee et excentree a gissant sur une bande rigide ont ete calcules pour le rapport H/B=1·0, 2·0 et 3·0, H etant l'epaisseur de la couche ...

The Dynamic Penetration Test: A Standard that is not Standardized

Abstract: Synopsis The Paper presents a description and a discussion of the technique of making the so-called standard penetration test as used in North and South America. Dynamic penetration tests such as t...