Estimation of capacity decrease due to accumulated excess pore pressures around cyclically loaded offshore foundations in sand

Abstract

In particular during storm events, a build-up of excess pore pressures may occur in the soil around cyclically loaded offshore foundations. Such accumulated excess pore pressure reduces the effective stresses in the soil and hence negatively affects the structural integrity. Even though the consideration of this degradation effect on the bearing capacity is commonly demanded by the involved certification or approval bodies, no generally applicable and accepted method for the calculative verification currently exists. The paper presents an approach which allows for the transfer of the soil behaviour observed in cyclic direct simple shear tests to the foundation structure system by means of a three-dimensional numerical model. The method is modular and can easily be assessed with engineering judgment in each substep. The used approach enables the consideration of site-specific cyclic laboratory test results by taking into account the mean stress, the cyclic shear stress amplitude and the number of load cycles at each integration point of the numerical model. Hence, the numerical approach may contribute to the optimisation of common foundation solutions as well as to the verification of innovative foundation structures even in complex soil conditions.