A computer model for the stress–strain behaviour of London Clay has been developed for use in a nonlinear finite element program. The behaviour of London Clay is divided into three ranges of strain: elastic, intermediate and plastic. In the elastic range strains are very small and the material is very stiff. The intermediate range represents the larger strain behaviour normally observed in laboratory tests; it is not truly elastic, but in many respects exhibits aniso-tropic elastic behaviour. As yield is approached, plastic behaviour can accompany the intermediate phase and is governed by a flow rule and a state boundary curve. In all phases the stiffnesses of the model increase with mean normal effective stress. It is shown that the model can be used to compute the results of both laboratory and in situ tests. The movements around two excavations in London Clay, including the New Palace Yard Underground Car Park, have also been computed retrospectively with considerable success. Un modèle informatique destiné à refléter le comportement contraintes-deformations de l'Argíle de Londres a été mis au point en vue de son emploi dans un programme non linéaire à éléments finis. Le comportement de l'Argile de Londres se divise en trois domaines de déformation: élastique, intermédiaire et plastique. Dans le domaine élastique, les déformations sont très faibles et le matériau est très rigide. Le domaine intermédiaire représente les déformations plus importantes que l'on observe normalement dans les essais en laboratoire; il n'est pas véritablement élastique mais présente à bien des égards un comportement élastique anisotrope. Lorsque l'on approche de la limite d'élasticité, on peut observer un comportement plastique dans la phase intermédaire, et ce comportement est régi par une loi de fluage et une courbe de limite entre états. Dans toutes-les phases, la rigidité du modèle augmente en fonction de la contrainte efficace moyenne normale. L'article montre que le modèle peut servir à déterminer les résultats obtenus aussi bien en laboratoire qu'in situ. Le calcul rétrospectif des mouvements enregistrés autour de deux excavations effectuées dans l'Argile de Londres, dont le Parking Souterrain du New Palace Yard, a également été effectué avec beaucoup de succès.
Using embodied energy as a quantitative measure of environmental impact, this study evaluated the embodied energy of two built sections of the UK Channel Tunnel rail link, now known as High Speed 1, and an alternative design. Results show that contract 220's 7·15 m diameter twin bored tunnel section of 7·5 km has an embodied energy of 949 TJ, whereas 7·3 km of contract 310's, consisting mainly of a pile-slab structure, consumed 678 TJ. The alternative design for contract 310, based on a conventional embankment design, would have consumed 640 TJ. By examining the embodied energy content, these geotechnical structures can be categorised into the following two types: (a) structures of which the materials are totally dominant at 90% of the total energy, such as pile-slab; and (b) more direct energy-intensive constructions, where the transportation and installation can collectively account for as much as 40% of the total, such as the tunnel and the embankment. In both types materials are generally the dominating energy consumer: therefore engineers should optimise designs using fewer embodied energy-intensive materials. When compared with the annual UK household energy consumption, the embodied energy values of these structures are equivalent to over 10 000 annual households' consumption. This comparison reveals the large scale of energy involved in geotechnical infrastructure construction, compared to activities in everyday life. This calls for more attention to evaluate the embodied energy of geotechnical constructions as part of design evaluations.
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