FEM-FDM coupled liquefaction analysis of a porous soil using an elasto-plastic model

150

In this paper, a new constitutive model is proposed to describe the mechanical behaviors of soils under diŠerent loading conditions. New evolution equations for the development of stress-induced anisotropy and the change of overconsolidation of soils are proposed. By combining systematically the above two evolution equations with the evolution equation for the structure of soil proposed by Asaoka et al. (2002), the newly proposed model is able to describe not only the mechanical behavior of soils under monotonic loading, but also the behavior of soils under cyclic loading with diŠerent drained condition. Special attention is paid to the behavior of sand subjected to cyclic loading under undrained condition. That is, for given sand with diŠerent densities, very loose sand may liquefy without cyclic mobility, medium dense sand will liquefy with cyclic mobility while dense sand will not liquefy, which is just controlled by the density, the structure and the anisotropy of the sand. A suitable model should uniquely describe this behavior without changing its parameters. Present research will show the possibility of the proposed model.

Section: Introductionmentioning

confidence: 99%

Explanation of Cyclic Mobility of Soils: Approach by Stress-Induced Anisotropy

Zhang

Yao

Noda

et al. 2007

150

“…The discretization scheme for the water phase is similar to that used in the liquefaction analysis method (e.g. (Oka et al, 1994). It is known that the FVM is applicable to the geometrically complicated region without variable transformation due to the arbitrary use of the grids, e.g., the unstructured grids.…”

Section: Mpm-fdm Coupled Formulation For the Simplified Three-phase Mmentioning

confidence: 99%

A Coupled MPM-FDM Analysis Method for Multi-Phase Elasto-Plastic Soils

Higo

Oka

Kimoto

et al. 2010

Self Cite

The Material Point Method (MPM), as proposed by Sulsky et al. (1994), has been developed to simulate large deformations and failure evolution involving diŠerent material phases in a single computational domain. A continuum body is divided into aˆnite number of subregions represented by Lagrangian material points, while the governing equations are formulated and solved with the Eulerian grid. Since this grid can be chosen arbitrarily, mesh tangling does not appear in the MPM. To design a simple but robust spatial discretization procedure, the MPM is coupled with theˆnite diŠerence method (FDM) in the present study for simulating fully and partially saturated elasto-plastic soil responses based on the simpliˆed three-phase method. Governing equations for the soil skeleton and the pore ‰uid are discretized by the MPM and FDM, respectively. Soil-water coupled analyses for fully saturated soils and seepage-deformation coupled analyses for unsaturated soils are performed, and the potential of the proposed method is demonstrated via numerical examples.

“…A lot of research has been conducted on the liquefaction of soils experimentally and theoretically at an element level toˆnd out a suitable constitutive model based on which numerical simulation usingˆnite element method (FEM) can be applied to a boundary value problem (BVP) of the liquefaction of soils. Some research related to constitutive model for liquefaction of sandy soils and corresponding numerical analysis using FEM can be found in the works by Oka et al (1992Oka et al ( , 1999, in which a constitutive model for sand, using the kinematic hardening rule, was proposed and applied to BVP by a soil-water couplingˆnite diŠerence-nite element (FD-FE) analysis with the code of LIQCA (Yashima et al, 1991;Oka et al, 1994). K. Nakai (2008) reported a very interesting study on the prediction of countermeasures for earthquake-induced consolidation deformation of river dike, where the analysis was carried out using FEM using an elasto-plastic constitutive model proposed by Asaoka et al (2002) employing the collapse of soil skeleton structure (the concept of superloading), the loss in overconsolidation (the concept of subloading), and the development of anisotropy during shearing.…”

Section: Introductionmentioning

confidence: 99%

Numerical Simulation of Sand Subjected to Cyclic Load Under Undrained Conventional Triaxial Test

Jin

Yan

Zhang

2010

In this paper, based on a elastoplastic model that can properly take into consideration the in‰uences of the density, the structure formed in depositary process and the stress-induced anisotropy of soils, 2D and 3Dˆnite diŠerence-ˆnite element analyses considering the soil-water coupling problems are conducted to simulate element test of sand specimen subjected to cyclic load under diŠerent loading conditions in triaxial test using the code named as DBLEAVES. In the element test, through stress-strain relation is regarded as uniform within the specimen of soil, it is usually non-uniform in reality. Due to limitation of element test devices for soils in laboratory test, a perfect element test is impossible in reality due to some factors such as an initial imperfection of test specimen, friction between loading plates and specimen, gravitational force of specimen and etc. It is, therefore, necessary to answer the question whether the results of an element test commonly used in laboratory test are convincing in determining the mechanical behaviours of the soils. If the answer is yes, then how much is the in‰uence of these factors on the tests which is usually regarded as an element behaviour. In the simulation, the element is considered as a boundary value problem. The in‰uence of those factors such as amplitude and frequency of cyclic loading, conˆning stress is also considered in detail. In the simulation, all values of material parameters are kept the same, which makes the numerical simulation being meaningful.