Impact of hyper-elasticity on cyclic sand modelling: A numerical study based on SANISAND-MS

Accurate simulation of foundation response subjected to repeated loading require reliable sand constitutive models to reproduce realistic sand cyclic behaviour. Many elastoplastic constitutive models adopted the hypoelasticity law, which results in physically inaccurate strain accumulation prediction of soil when subjected to elastic cyclic loading. To address this issue, the existing elastoplastic bounding surface model SANISAND-MS has been upgraded with a hyperelastic formulation that is derived from the Helmholtz free energy function. The complete form of the derived nonlinear elasticity functions enhanced by stress induced anisotropy is presented in this work. The calibration of the upgraded SANISAND-MS is briefly discussed. It is demonstrated that the hyperelastic formulation with volumetric-deviatoric coupling: (1) guarantees no accumulation of elastic strain upon elastic cyclic loading, and (2) captures the stress-induced anisotropy of sand under reverse loading. This upgraded SANISAND-MS model with a physical adaptation and thermodynamically consistent elasticity law can predict strain accumulation accurately and is physically appropriate. Moreover, the upgraded SANISAND-MS is suitable for simulating problems with high-cyclic loads and is able to be used in boundary value problem simulations in areas including offshore engineering and railway engineering.