Application and challenges of fibre optic pore pressure sensors in centrifuge testing for monitoring pile jacking in clay

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4. Application and challenges of fibre optic pore pressure sensors in centrifuge testing for monitoring pile jacking in clay

Soil plugging during the installation of open-ended piles has been target of numerous scientific investigations which almost exclusively focused on sandy soils, while the plugging behaviour in cohesive soils to this day is relatively unknown. The development of excess pore pressures and the resulting change in effective stresses inside the pile during its installation is expected to be the main influencing factor on soil plug formation. To receive a better insight into the mechanisms during pile installation, centrifuge tests were performed at TU Delft. Herein, the measurement technique of fibre optics allowing stress determination through Fabry-Pérot pressure sensors was employed and tested in its capabilities. Model piles were instrumented with total stress sensors together with fibre optic sensors measuring pore water pressure development. Two different piles were installed in flight at 50 g into artificial clay samples giving results of three pile jacking processes. The setup allowed for measurement of pore water pressure build-up inside and outside the pile. From this, a back-calculation of the effective stresses and a comparison between inner and outer radial stresses was made. However, the results indicate room for future improvement as a full saturation of the system is required to determine pore pressures accurately. The employment of fibre optic sensors in centrifuge testing for pore pressure determination is believed to be of great potential but requires further validation.

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