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Determination of soil shear modulus at low strain level using an innovative pressuremeter probe : Application to cyclic pile design.

Abstract : Many civil engineering structures are subjected to cyclic loading of environmental types (e.g. waves or earthquakes) or industrial types (e.g. rails or roads). Some of these constructions are supported by deep foundations (piles), which must resist the vertical or lateral components of the cyclical efforts. In general, this results in degradation of the bearing capacity of the piles by modifying the properties of the soil-structure interface, which should be considered for design. In France, current design methods of deep foundations are based primarily on the results of pressuremeter tests and concern only the monotonous loads. On the other hand, the existing methods enabling the design of piles under axial or lateral cyclic loads are based on soil parameters obtained from laboratory tests, and this approach does not fit in the French daily practice. This thesis is inserted in the context of the National Project ARSCOP (“improvement of the ground investigation and the design of geotechnical structures with the use of pressuremeter”). Its main objective is the development of a new methodology for the design of deep foundations under cyclic loads using the pressuremeter test. However, it has been found that it is not possible to obtain significant soil parameters for the design of this type of structure, namely soil shear moduli at small strain levels, using the pressuremeter testing equipment and the procedures currently available. In this work, we propose the use of an innovative pressuremeter probe, developed by a partner, as well as the testing procedures necessary to reach the proposed goal. As a first step, we defined a laboratory testing program for the validation of the measurement capabilities of this new device. Tests were carried out in a calibration chamber, in dry Fontainebleau sand specimens, reconstituted at different density indices. Emphasis was placed on determining the shear modulus in a range of small strains, between 10-4 and 10-2. Tests have also been carried out to assess the behavior of the soil under repeated cyclic loading. The second part consisted in validating the measurement capabilities of this probe from in situ tests. Two reference test sites were chosen, Dunkirk and Merville (dense sands and overconsolidated clays, respectively), on which the soil characteristics, assessed using different ground investigation methods, were previously known. Results of full-scale cyclic axial pile load tests carried out at these sites were also available. The results obtained with the new pressuremeter device according to the methodology developed in this thesis were then used to illustrate possible engineering applications, with emphasis on the design of piles under axial cyclic loading. The validation was made by comparison with the behavior measured in the pile loading tests available on the reference sites
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Alexandre Lopes dos Santos. Determination of soil shear modulus at low strain level using an innovative pressuremeter probe : Application to cyclic pile design.. Géotechnique. Université Paris-Est, 2020. English. ⟨NNT : 2020PESC1015⟩. ⟨tel-03267716⟩

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