The mechanism of the lateral reaction of piles in an elastic-plastic medium is examined. Plane strain is first assumed. The analytical solution for a circular section in an elastic medium is given. The influence of pile section (square pile), disturbance of a soil ring around the pile, plastic yield of soil in undrained behaviour (Tresca's criterion) are studied by means of the finite element method. All these factors affect strains and stresses only in the vicinity of the pile. Graphs are given making it possible to calculate the corresponding corrective terms to be applied to the analytical solution. In a second step, which defines the value of the outside radius of this two-dimensional model, the simplified three-dimensional problem of a horizontally-loaded vertical axis in a semi-infinite elastic solid is studied using Mindlin's solution for a point force. The influence of the relative soil-pile rigidity, head loading and fixing conditions, which have an effect especially on distant fields, are taken into account and quantified by simple rules for determining this outside radius. Finally, a specific numerical application of the results is made and the solution is very satisfactory compared with experimental measurements. On étudie le mécanisme de réaction latérale des pieux en milieu élasto-plastique. On suppose tout d'abord que la déformation est plane. La solution analytique pour une section circulaire dans un milieu élastique est donnée. Les influences de la forme de la section du pieu (pieu carré), du remaniement d'un anneau de sol autour du pieu, de la plastification du sol en comportement non drainé (critère de Tresca) sont étudiées à l'aide de la méthode des éléments finis. Tous ces facteurs ne jouent sur le champ des déformations et des contraintes que dans le voisinage du pieu. Des abaques sont donnés, permettant de calculer les termes correctifs correspondants, à appliquer à la solution analytique. Dans un deuxième temps, pour préciser la valeur à prendre en compte du rayon extérieur de ce modèle bidimensionnel, on étudie le problème tridimensionnel simplifié d'un axe vertical chargé horizontalement dans un massif élastique semi-infini, en sommant la solution de Mindlin pour une force ponctuelle. Les influences de la rigidité relative sol-pieu, des conditions de chargement et d'encastrement en tête, qui affectent surtout les champs au loin, sont ainsi prises en compte et quantifiées par des règles simples de détermination de ce rayon extérieur. Enfin une application numérique concrète des résultats est faite et la solution est très satisfaisante, comparée aux mesures expérimentales.
An instrumented pipe pile has been installed in an unstable slope to measure long-duration P–Δy lateral reaction curves. After outlining the main features of the experiment, results are given over a period of 16 years. These comprise the soil movements, the pile displacements, the bending moments and the reaction pressures. A Ménard pressuremeter method and a self-boring pressuremeter method are used to predict the P–Δy reaction curves, which are then used in a numerical model to derive the overall pile behaviour. The results are compared with measured pile displacements and bending moments and show that the pile displacements and bending moments calculated by the numerical model are markedly overestimated.
RESUME: Afin d'étudier l'effet de groupe sur des pieux chargés latéralement, des essais sur modèles réduits de couples de pieux ont été réalisés avec la centrifugeuse du Laboratoire Central des Ponts et Chaussées. Une méthode a été établie pour obtenir les courbes de réaction P-y à partir des résultats expérimentaux. On compare ensuite ces courbes à des codes de calcul reconnus : Fascicule 62 (France), Port and Harbour Research Institute (Japon) et l'American Petroleum Institute (D.S.A). Les déplacements en tête et les profils de moments fléchissants obtenus permettent de déterminer l'effet de groupe. On établit finalement des coefficients de réduction sur la réaction latérale du sol.
International audienceThe load transfer method is an efficient and practical tool for the analysis of single piles and combined systems such as pile-raft foundations and rigid inclusions. The existing transfer curves rely either on the measurement of the pressuremeter modulus, which is not widespread at the international level, or they have been developed only for specific pile and ground types. In order to develop new transfer curves valid for all pile and ground types without the need of pressuremeter tests, a database of 50 instrumented pile load tests was examined. The existing curves were first compared to the measurements at the pile shaft and at the tip. Then the parameters of the most appropriate curve types, the cubic root and the hyperbolic curve, were calibrated in order to best match the measurements. A single set of parameters for each proposed curve type is suitable enough for most pile and ground types. The good agreement of the proposed curves was confirmed by applying them to assess the overall load-settlement curve of 72 other pile load tests
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