The development and evaluation of a constitutive model for the prediction of ground movements in overconsolidated clay

Abstract

The stress—strain response of overconsolidated clay depends both on its current state and on the loading history followed to reach that state, in particular the relative directions of the current and previous loading paths. A constitu-tive soil model is developed which predicts this behaviour by allowing elasto-plastic deformations controlled by two nested kinematic hardening surfaces inside a conventional Modified Cam-clay state boundary surface. This relatively straightforward model requires only eight para-meters, each with a rational basis, and which can be determined from a small number of well-controlled stress path tests. Predictions of soil behaviour using this model are compared with data from triaxial stress path tests. The close agreement confirms that the essential features of soil behaviour are predicted by the model. The wider implications of the use of the model in geotechnical analysis are illustrated by compar-ing predictions made using the model (in conjunction with finite element analysis) with data from a specially commissioned series of centrifuge tests of a circular foundation loaded on overconsolidated clay. The stress history of the soil was carefully controlled in the experiments and was replicated in the course of the analyses. The computations reproduced the main characteristics of the observed ground movement, in particular the surface profile. In contrast, conventional constitutive models of soil behaviour show very poor predictions. This demonstrates the importance of using a model that simulates the behaviour of soil over a wide range of strain increments and with changes in load path direction. La réaction tension/déformation de ĺargile préconsolidée dépend à la fois de ĺétat de ĺargile et des charges antérieures, notamment des directions relatives de la charge présente et des charges précédentes. ĺexposé décrit un mod&gave;le de sol constitutif qui prédit ce compor-tement en permettant des déformations élastoplastiques engendrées par deux surfaces ciné matiques de durcissement emboîtées dans une surface limite classique ´argile du Cambrien modifiée. Ce modèle relativement simple ńexige que huit paramètres, chacun avec une base rationnelle, et pouvant être déterminés à pardr ´un petit nombre ´essais bien contrôlés des parcours de tension. Les prédictions du comportement du sol faites à ĺaide de ce modèle sont comparées aux données fournies par des essais triaxiaux des parcours de tension. La bonne corrélation entre les deux ensembles de valeurs confirme que le modèle pent prédire les caractéristiques essentielles du comportement du sol. ĺexposé illustre les autres applications possibles de ce modèle à ĺanalyse géotechnique en comparant les prédictions faites à ĺaide du modèle (en conjunction avec une analyse des é1éments finis) aux données fournies par une série spéciale ´essais centrifuges ´une fonda-tion circulaire chargée sur de ĺargile prĺcon-solidée. On a soigneusement documenté les tensions successives dans les essais pour pouvoir les reproduire dans les analyses. Les calculs ont reproduit les principales caractéristiques du mouvement de sol observé, notamment le profil de surface. Par contraste, les modéles constitu-tifs classiques du comportement du sol donnent de très mauvaises prédictions. Cela montre qúil est important ´utiliser un modèle qui simule le comportement du sol sur une vaste gamme de tensions et avec des changements de direction des charges.

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

“…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):…”

“…A -Current stress state B and C -conjugate points with the same outward normal as A γ -vector of movement of yield surface parallel to AB and of magnitude AB β -vector of movement of yield surface parallel to BC and of magnitude BC (Stallebrass and Taylor, 1997).…”

“…In this section the ability of the 3-SKH model to predict the earth pressure coefficient was investigated. The results were obtained using the CRISP finite element program with four cubic strain triangular elements and the parameters used in the simulation are those for kaolin from Stallebrass (1997) given in (Stallebrass and Taylor, 1997). Schmidt (1966).…”

“…The 3-SKH model has been shown to be able to predict the essential features of soil behaviour under monotonic loading (Stallebrass and Taylor, 1997). A preliminary evaluation of the model's ability to predict soil behaviour under cyclic loading was performed using the finite element program CRISP (Britto and Gunn, 1987).…”

“…In this chapter, the model parameters for kaolin clay are determined by triaxial testing using the methods proposed by Stallebrass (1997 …”