Investigations of vertical bearing capacity of open-ended piles in cohesive soils with respect to soil-plug formation

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Soil plugging in open-ended piles until now was mainly investigated regarding installation in granular soils. In the present research project, the aim is to investigate the mechanisms of soil plug formation during the installation of open-ended piles in cohesive soils.Thus, it is planned to carry out in-site as well as centrifuge tests regarding the installation of tubular piles into cohesive soils. On the one hand, during the in-site tests a realistic stress state can be considered at the best. On the other hand, centrifuge tests are used for tests under reproducible conditions as well as well defined soil mechanical boundary conditions. Especially, centrifuge tests are well suited for model testing in geotechnical engineering as the applied stress-state realistically reproduces in-site conditions. Furthermore, during centrifuge testing it is possible to investigate a wide range of influencing parameters (e.g. consolidation state, installation method, pile diameter) regarding soil plugging tendency.The tests are evaluated regarding the internal stress development inside the open-ended piles as indicator for arching and following a soil plug formation. Out of these results, general conclusions regarding the mechanisms of soil plugging in cohesive soils with respect to the main influencing parameters are drawn.Accompanying laboratory and element tests lead to better undestanding of the investigated cohesive soils especially in context with pile shaft-soil-interaction.Besides, a feasibility study regarding the possibilities to numerically simulating the soil plugging process during installation of open-ended piles into cohesive soils is carried out. In this framework, the results of centrifuge as well as in-site testing are used to investigate possibilities and limitations of different numerical modelling approaches (CEL, DEM, SPH) regarding soil plugging during pile installation in cohesive soils. Main aim of this work package is to validate the numerical models such that they can be used in future research.Finally, all results are consolidated to develop an analytical approach for prognosis of vertical pile resistance of open-ended piles installed in cohesive soils with respect to sthe oil plugging and its main influencing parameters. Thus, an approach will be developed to predict vertical capacity of a plug in cohesive soils based on an internal effective earth pressure coefficient in the area of a possible soil plug as it was succesfully developed by the applicant during a preceding DFG-research project regarding the installation of open-ended piles in granular material.