Stiffness of fine-grained soil at very small strains

Abstract

The stiffness of soil at very small strain Go is a useful parameter for characterizing the non-linear stress–strain behaviour of soil for monotonic loading and it is required for analyses of the dynamic and small strain cyclic loading of soils. Tests were carried out on fine-grained soils in a hydraulic triaxial cell fitted with bender elements and with local axial gauges. From the results of these tests simple expressions were obtained which describe the variation of G>o with current state in terms of the current stress and overconsolidation ratio. The parameters in these expressions were found to depend on plasticity index. The simple expressions for Go were found to apply generally at larger strains, with the values for the parameters also depending on the current strain. Values of Go measured in laboratory tests on reconstituted London clay agree well with values measured in tests on undisturbed samples and in field tests which make allowance for the different states in the various tests. La rigidité Go d'un sol, sous très faible déformation, est un paramètre intéressant qui permet de caractériser la non-linéarité du comportement en contrainte-déformation de ce sol lors d'un chargement monotone et d'analyser les cycles de chargement dynamique à faible déformation. Des essais ont été réalisés en cellule triaxiale hydraulique sur des sols finement grenus équipés de capteurs en flexion et de jauges axiales locales. Les résultats obtenus au cours de ces essais ont permis de définir des relations simples donnant la variation de Go en fonction de la contrainte courante et du degré de surconsolidation. Les paramètres dépendent de l'indice de plasticité. Une expression simple de Go est applicable à de plus fortes déformations, les paramètres étant alors en plus fonction de la déformation courante. Les valeurs de Go mesurées en laboratoire sur de l'argile de Londres reconstituée sont en bon accord avec celles obtenues sur des échantillons intacts où lors d'essais in-situ et rendent compte des différents états rencontrés lors des différents essais.

The application of a three-surface kinematic hardening model to repeated loading of thinly surfaced pavements

“…These charts were derived from test data for different soil types with different plasticity indices. The coefficients A, m, and n obtained by Viggiani and Atkinson (1995) for Speswhite kaolin clay were 1964, 0.2, and 0.65.…”

“…the shear modulus at very small strains and κ * is the initial slope of the isotropic swelling line in ln v − ln p' space. The value of G' e can be assumed to vary with p' and overconsolidation ratio, R o according to the relationship proposed by Viggiani and Atkinson (1995) (Stallebrass and Taylor, 1997):…”

“…However, these can be determined approximately if the plasticity index of the soil is known (Viggiani and Atkinson, 1995).…”

“….7. The coefficients A, m, and n can be obtained from Figure 5.10 produced by Viggiani and Atkinson (1995) if the plasticity index is known. These charts were derived from test data for different soil types with different plasticity indices.…”

“…From Figure 5.10, for soil with PI = 32% the coefficients A, m, and n are approximately 1,000, 0.8, and 0.24 respectively. (Viggiani and Atkinson, 1995). (ii) T and S The parameters T and S that determine the size of the history and the yield surfaces were determined by isotropic unloading and reloading as described by Stallebrass (1997), see Section 3.2.3.…”