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
This article presents the experimental procedures performed in a laboratory to evaluate the measuring capabilities of an innovative monocellular pressuremeter probe. This probe takes advantage of recent technological developments in the domain of inflatable membranes currently applied in the so-called Francis Cour standard tricellular probes, which allow covering an expansion range up to large cavity strains. Those improvements were found to enable increasing the accuracy in the assessment of radial expansion through volume injection in the probe measuring cell at relatively small strain levels without the need of sophisticated punctual measuring arms. Assessing this domain via in situ tests makes up a major contribution to the design of geotechnical structures under cyclic loads, for which the current design practice is mainly developed through laboratory soil tests. To reach this final objective, the probe’s validation program was launched based on pressuremeter tests with unload-reload loops performed in a laboratory calibration chamber and in situ on reference testing sites. This paper focuses on the laboratory testing protocols performed in dry Fontainebleau sand specimens. Shear moduli obtained with the pressuremeter are compared with the expected elementary values for this sand, and it is shown that it was possible to assess sand stiffness at a small strain level using this probe under controlled conditions in a laboratory.
This paper presents an experimental study aimed at evaluating the measuring capabilities of an innovative monocellular pressuremeter probe, the Monocell Francis Cour probe, based on calibration testing in the laboratory. The originality of the tested equipment is to allow evaluation of soil properties in both small- and large-strain domains, without the need of sophisticated point displacement measuring arms. This paper focuses on the evaluation of small-strain shear modulus G of Fontainebleau sand, NE34, based on tests carried out with this specific pressuremeter probe. Shear modulus values obtained with this probe are then compared with values resulting from more classical elementary tests, showing a fairly good consistency. It is shown, with satisfactory agreement, that it is possible to quantify the influence of the density index of the sand as well as the influence of the mean effective stress around the probe on the shear modulus, based on the analysis of specific unload−reload loops performed during the test. The experimental programme carried out under well-controlled laboratory conditions allows a validation to be proposed for a method of derivation of the shear modulus of sand at small strain levels using this prototype pressuremeter.
L’essai au pressiomètre Ménard est l’essai de référence pour la reconnaissance des sols en vue du dimensionnement des ouvrages géotechniques en France. Réalisé selon les normes en vigueur, il fournit un paramètre de déformation et de rupture du sol, respectivement le module pressiométrique Ménard et la pression limite pressiométrique. Ces paramètres peuvent être utilisés pour la conception de fondations superficielles et profondes sous chargements monotones, en s’appuyant sur des méthodes bien établies et comprises dans les normes d’application nationales françaises de l’Eurocode 7. Cependant, pour certaines structures telles que les fondations soumises à des charges cycliques répétées, les paramètres de calcul à prendre en compte correspondent à un niveau de déformation plus faible, qui ne peut être évalué à l’aide des procédures et des équipements pressiométriques usuels. Cet article présente le travail mené dans le cadre de la thèse de doctorat lauréate du Prix Boussinesq 2021 (Lopes A. 2020. Determination of soil shear modulus at low strain level using an innovative pressuremeter probe. Application to cyclic pile design. Thèse de doctorat). Cette thèse avait pour objectif le développement d’une nouvelle méthode de dimensionnement des fondations profondes sous charges axiales cycliques en utilisant l’essai pressiométrique. La recherche était inscrite dans le contexte du Projet National ARSCOP (nouvelles Approches de Reconnaissance des Sols et de la Conception des Ouvrages géotechniques avec le Pressiomètre). La démarche suivie permettant de surmonter les limitations de la pratique pressiométrique actuelle sera présentée, ainsi que la sonde innovante utilisée et les procédures d’essai et d’interprétation proposées. Les résultats obtenus, d’abord en condition d’essai contrôlée en chambre d’étalonnage au laboratoire, et puis en conditions réelles in situ, permettant de valider les procédures, sont présentés et discutés. Les applications à la pratique de l’ingénierie sont ensuite discutées.
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