ABSTRACT

Offshore structures, as for instance offshore wind turbines, are subjected to combined static and cyclic loading from wind, waves and current. To be able to perform an optimised design of the foundation of these structures it is important to account for the characteristic behaviour of the soil under these irregular load conditions. This paper presents detailed interpretation of undrained, partly drained and drained monotonic and cyclic triaxial tests on a typical dense North Sea sand within an elasto-plastic framework. The incremental shear (or deviatoric) strain is given by a plastic hardening modulus and the ratio between the incremental plastic volumetric strain and shear strain by a dilatancy parameter. The plastic strain increments are derived from the total strains by first subtracting the elastic strains from the measured total strains. The variations of the hardening and dilatancy parameters are presented as function of mobilised friction. In addition, the rate of shear strain and pore pressure accumulations are presented. Then, the interpreted results are compared with values obtained from the equations used in the SANISAND model. Based on this, limitations in the existing formulation of the SANISAND model are discussed. The presented results may further be used to improve existing models for cyclic behaviour of water saturated dense sands.