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

In heavily over-consolidated clays there is a marked peak in the observed relation between shear stress and shear strain. As the strain increases, the stress falls from a peak to a much smaller residual stress. Slopes made from such a clay often fail progressively many years after construction. Sliding occurs on a concentrated slip surface, and it is found that the mean resolved shear stress on that surface is markedly less than the peak shear strength. Concepts from fracture mechanics, and in particular the J -integral, are used to derive conditions for the propagation of a concentrated shear band of this kind. The results indicate the presence of a strong size effect, which has important implications for the use of models in soil mechanics. An elastic analysis makes it possible to determine the size of the end zone in which the shear stress on the shear band falls to its residual value. An attempt is made to assess the possible sources of the time-dependence governing propagation speed of the shear band. They include pore-water diffusion to the dilating tip of the band (which governs the rate at which local strength reductions can occur), viscoelastic deformation of the clay (which allows a gradual build-up of strain concentration at the tip of the band), and the weathering break-down of diagenetic bonds.

The Growth of Slip Surfaces in the Progressive Failure of Over-Consolidated Clay

Synopsis The Paper gives a review of the various geological processes which can take place with time in the Norwegian normally-consolidated marine clays, and which will lead to changes of the geotechnical properties. Most attention is paid to changes in compressibility and the effects of the various processes discussed are illustrated by a collection of records of settlement of buildings in Drammen, a town located 40 km south-west of Oslo. The processes considered are: leaching, delayed consolidation, exchange of cations on clay minerals, and bonding of the clay structure by precipitation of cementing agents. The process of delayed consolidation is dealt with in detail. It is demonstrated that delayed consolidation leads to the development of a reserve resistance against compression under additional loads. A diagram is presented which permits a qualitative evaluation of the settlements of the buildings founded on clays exhibiting delayed consolidation. The general validity of the concepts presented is dem...

Engineering geology of Norwegian normally consolidated marine clays as related to settlements of buildings

Introduction to Soil Mechanics and Foundations. Physical Characteristics of Soils and Soil Investigations. Stresses, Strains and Elastic Deformations of Soils. One--Dimensional Consolidation Settlement of Fine--Grained Soils. Shear Strength of Soils. A Critical State Model to Interpret Soil Behavior. Bearing of Capacity of Soils and Settlement of Shallow Foundations. Pile Foundations. Two--Dimensional Flow of Water Through Soils. Stability of Earth Retaining Structures. Slope Stability. Appendices. Answers to Selected Problems. References. Index.

Soil Mechanics and Foundations

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 Paper gives a short description of a recently developed direct simple-shear apparatus. The cylindrical sample (diameter 8 cm, height 1 cm) is confined in a reinforced rubber membrane allowing vertical deformations and horizontal displacements with no change in diameter. Consolidated constant-volume shear tests showed shear strengths which were lower than those found in comparable triaxial tests. The ratio of the constant-volume shear strength to vertical consolidation pressure with the new equipment was found to be 0·18 compared with 0·29 measured in the triaxial tests and 0·13 found by vane tests in situ. The drained tests on samples consolidated at a pressure equal to the overburden in the field indicate that the structure of the clay might be stable for small shear stresses but starts to collapse at a certain critical value. This phenomenon might contribute to explain some landslides which have occurred in slopes in quick clay at a shear stress much below the ultimate drained shear strengt...

Direct Simple-Shear Tests on a Norwegian Quick Clay

Synopsis The majority of the late glacial marine clays in Norway have been subjected to a leaching by fresh water due to a land elevation, resulting in a reduced salt concentration in the pore wate...

Geotechnical Properties of Norwegian Marine Clays

Synopsis The settlement of a foundation on a saturated clay is composed chiefly of the “immediate” settlement due to deformations taking place at constant volume, and the “consolidation” settlement due to volume reduction consequent upon the dissipation of pore pressures. This latter component is therefore dependent on the pore pressures set up by the foundation load, and these pore pressures are themselves dependent on the type of clay. An approximate theory is described which takes account of the type of clay; and comparisons with observed settlements in a number of practical cases show the theory to be an improvement on existing methods of calculation. Le tassement d'une fondation sur une argile saturee se compose principalement du tassement “immediat” du aux deformations ayant lieu suivant une ampleur constante, et le tassement “de consolidation” du a la diminution d'ampleur parsuite de la dissipation de la pression interstitielle. Cette derniere composante depend done des pressions interstitielles pr...

A Contribution to the settlement analysis of foundations on clay

Owing to the development of oil and gas fields in the North Sea, the Norwegian Geotechnical Institute has in recent years become involved in extensive investigations of the sea bed. Work has been c...

Laurits Bjerrum

Papers

Engineering geology of Norwegian normally consolidated marine clays as related to settlements of buildings

Direct Simple-Shear Tests on a Norwegian Quick Clay

Geotechnical Properties of Norwegian Marine Clays

A Contribution to the settlement analysis of foundations on clay

Geotechnical problems involved in foundations of structures in the North Sea