Speswhite Kaolin Research Articles

Numerical Analysis of Soils in Simple Shear Devices

ABSTRACT The results of finite element analyses of soils in simple shear devices, assuming that these soils can be modelled either as an elastic or an elastoplastic material, are presented. The results indicate that an elastic analysis produces larger levels of stress concentrations than an analysis using the modified Cam-clay model. The predicted stress-strain behavior of a very loose sand and speswhite kaolin using the modified Cam-clay model agrees very well with simple shear test results deduced from measurements made at the sample core of the top boundary of the samples for constant load tests. A satisfactory match of experimental and modified Cam-clay stress-strain results was not obtained for the constant height test. The simple shear devices (Norwegian Geotechnical Institute and Cambridge types) can be expected to give good quality results for monotonic loading from carefully prepared samples if measurements of stress and pore water pressures are made at the sample core on either the top or bottom or both horizontal boundaries of the sample.

An experimental study of skin friction around piles in clay

Load tests on a model pile installed in Speswhite kaolin are described. The soil surrounding the pile was consolidated under a range of stress ratios K, and the pile was loaded under drained conditions in such a way that only shaft friction was generated. Pile installation techniques minimized soil disturbance so that the failure criterion for pile shaft friction could be investigated. The results, based on tests on nine normally consolidated and one overconsolidated sample, show that the angle of shaft friction is independent of the stress ratio in the soil before loading (0·7 <K <1·5), and is only justless than φ′triaxial for normally and overconsolidated kaolin. When loaded axially the lateral stresses on the pile shaft decrease with increasing shaft load for normally consolidated soil, and increase on loading in overconsolidated soil. Differences between adhesion factors α; back-calculated from the model tests and those normally encountered in practice highlight the effects of disturbance caused by most pile installation techniques. L'article décrit des essais de chargement d'un pieu-modéle mis en place dans le kaolin de Speswhite. Le sol entourant le pieu a été consolidé. successivement à différents rappart des contraintes principles K et le pieu a été chargé dans des conditions drainées de telle fa&cetil;on que seulement du frottement latéral soit mobilisé. La technique d'installation du pieu a minimiser le remaniement du sol de sorte que le critére de rupture par frottement latkral puisse être étudié. Les résultats, basés sur des essais effectés sur onze échantillons normalement consolidés et un échantillon surconsolidé, indiquent que l'angle de frottement sur le pieu est indépendant des rapports de contraintes dans le sol avant chargement (0·7 <K <l·5), et que sa valeur n'est que légérement inférieure à φ′ triaxial dans le cas du kaolin normalement consolidé et surconsolidé. Lors du chargement axial les contraintes latérals sur le fut du pieu décroissent au fur et à mesure que la charge de puits augmente dans du sol normalement consolidé, tandis qu'elles s'accroissent quand ladire charge croît dans du sol surconsolidé. Les différences entre les coefficients de frottement x calcués à parti du modéle et ceux habituellement rencontrts en practique font apparaitre clairement les effets du remaniement causé par laplupart des proédés de mise en oeuvre des pieux.