Photos of Yiru Chen visiting in CIMNE
Dr. Alessandro Franci showed us his work in particle finite element method and discrete element method. In addition, Kratos Multiphysics was introduced briefly, with its high performance and great extensibility being demstrated. It can be applied to fluid dynamics, structural mechanics and DEM fields of applications. This framework and software provides a new prespective into the numerical modelling in Multiphysics and multiscale simulations which could be useful in the future work.
With its objectives of advancing multiscale and Multiphysics modelling of localization phenomena in geomaterials, constitutive models play a key role part in the modelling of geomaterials behaviours, providing fundenmentals in understanding the evolution of in the hydraulic and mechanical characteristics.
A mechanical model accounting for the hysteresis behviour under wetting and drying is employed to describe the hydraulic responses under varying hydraulic loading conditions. The model is based on the classical model of soil water characteristic curve (SWCC) proposed by Fredlund and Xing, which defines the relationship between degree of saturation Sr and matric suction s in drying and wetting process as:
where ad, md, nd are the fitting parameters for the main drying branch and aw, mw, nw are for the main wetting branch. With the main branches defined, the shifting of SWCC due to mechanical loading process and wetting-drying path is described in an incremental form:
Typical hydraulic response under drying and loading cycles can be achieved using the above model.
In addition, hypoplastic model proposed by Wu is adopted to account for the mechanical behaviour of soils.
Similarly, the basic parameters can be determined by the compression index, fricition angel, and material constant. The compression index is expressed as the function of Sr according the work of Zhou et al.:
Therefore, the hypoplastic constitutive model can be composed of two parts, accounting for both mechanical and hydraulic loadings effect on the stress rate
Note that when dSr=0, the proposed equation returns to standard hypoplastic equation.
The result of volume and saturation under isotropic condition with the above model are illustrated in the figures below. The experimental and numerical results agree well both on the mechanical and hydraulic responses. The typical coupling effect between hydraulic and mechanical properties are shown with the increase of deformation related to the evolution of saturation during the wetting process.
Figure 1. Results of evolution of specific volume and saturation under wetting test at net stress of 588kPa.
With the proposed model, it includes an additional volumetric effect on stress-strain response. introduces an extra driving force due to changes in suction and saturation which can provide an insight into the information in the multiphysical problem.