In particular during storm events, an accumulation of excess pore pressures may occur even in sandy soil around cyclically loaded offshore foundations. The excess pore pressure build-up reduces the effective stresses in the soil and may affect the structural integrity negatively. Even though the consideration is commonly demanded by the involved certification or approval bodies, no general applicable and accepted method for the calculative verification currently exists. The paper presents a concept of a numerical method which allows the transfer of the soil behaviour observed in cyclic tests to the bearing behaviour of the entire foundation. Herein, the numerical model accounts for the cyclic excess pore pressure accumulation by considering the element-based vertical stress, the cyclic shear strain amplitude and the number of load cycles. The overall procedure is a simple tool for estimating the influence of storm loading on the post-cyclic capacity. For a typical monopile foundation in sand, results based on cyclic simple shear tests, which are primarily used in the current stage, are presented and discussed. The numerical approach may contribute to the optimization of common foundation solutions as well as to the verification of innovative foundation structures even in complex soil conditions.
Jann-Eike Saathoff and Martin Achmus
Keywords: cyclic direct simple shear, cyclic loading, excess pore pressure, post-cyclic capacity
Publisher: DFI