Physical modeling and numerical analyses of vibro-driven piles with evaluation of their applicability for offshore wind turbine support structures

Vibro-driven piles can potentially become cost-reducing alternatives to standard impact-driven piles for offshore wind turbine support structures. If these foundations are to be used to support jacket sub-structures, their bearing behaviour in tension has to be explored. In a novel geotechnical testing facility two large-scale vibro-driven piles for jacket sub-structures have been axially tested in tension. In this contribution the experimental tests are thoroughly described and the test results are presented. The applicability of standard CPT methods in predicting the tensile bearing capacity of the piles is evaluated against the experimental results. In addition, a simplified 2D axisymmetric numerical model is adopted to interpret the initial stiffness of the pile-soil interaction. As also pointed out in previous studies the ultimate resistance of the piles turns out to be significantly smaller than the CPT method prediction. Furthermore, as expected, set-up and pre-loading effects are seen to be beneficial to the tensile bearing behaviour of the pile.