Congratulations to Dr. Haoyuan Liu!
Haoyuan Liu successfully defended his PhD thesis entitled “Constitutive modelling of cyclic sand behaviour for offshore foundations”, on 1 October 2020.
The PhD project has contributed to the constitutive modelling of sandy soils under (high-)cyclic loading conditions, with emphasis on its use in 3D FE OWT foundations oil simulations. The phenomenological modelling of so-called ‘fabric effects’ (i.e., the impact of microstructural properties on soil’s stiffness and strength), and associated load induced anisotropy, has been centre stage of all theoretical developments. Such fabric effects and the stress history do influence severely sand’s (high) cyclic behaviour, for instance, in terms of strain accumulation response (ratcheting) and/or cyclic pore pressure build-up. Their numerical simulation at the level of a soil element has been achieved by implementing a ‘memory surface’ into the bounding surface plasticity model SANISAND2004, giving rise to the new, ‘memory enhanced’ SANISAND-MS model.
The proposed model has been implemented into OpenSEES and validated against a wealth of laboratory test results from the literature, spanning a variety of initial, loading, and drainage conditions. Following thorough validation of the constitutive equations, SANISANDMS has been then applied to the 3D FE analysis of a cyclically loaded monopile in dry sand, to assess the ‘implicit’ performance of the constitutive model in a relevant boundary value problem. Overall, the model appears capable of capturing cyclic soil behaviour and soil structure interaction at the scale of soil element and monopile foundation, respectively.
Haoyuan's PhD thesis can be found here.