GEOLAB-INXEMOS-Effect of installation and exploitation of monopiles in sands

The growing demand for renewable energy solutions result in continuous development of Offshore Wind Turbines (OWTs).  The superstructures of this renewable energy system is mostly supported on monopile foundations due to its simplicity to fabrication and installation in this harsh environment. Up to this day, there is uncertainty in the design of this type of foundation rising from the installation effects on the changes of the properties of the surrounding soil mass. Recent centrifuge and field testing, and numerical analyses show the installation effects in the lateral capacity of piles. Nonetheless, there is still need to understand the installation effect on the cyclic response of pile and the evolved stresses at the shaft of the pile. In view of thoroughly understanding this effect, a series of model pile tests are conducted in the centrifuge facility of TU Delft. The investigation concerns the cyclic and monotonic lateral response of instrumented open-ended piles jacked at different target g-levels in dry silica sand. Specifically, a comparative analysis of the lateral performance of piles installed at 1g and Ng is carried out. After the installation, the piles were laterally loaded at the target g-level. For this analysis, a new advancement in the actuator of TU Delft’s centrifuge lab is developed, which allows to perform tests in-flight without interrupting the centrifuge for adjustments in the actuator. The centrifuge analysis provides significant insights in the lateral capacity of piles, accumulation of lateral displacements under cyclic loading and radial stresses at the pile shaft. As expected, the lateral capacity of piles installed at Ng-level is greater, while the rate of displacement is smaller than piles installed at 1g-level. Remarkably, the former piles experience a rise in the stresses measured after their shaft during the first stages of the applied monotonic or cyclic load.