Evolution of the soil water retention curve based on plastic volumetric strain

The water retention behaviour of soil can be defined as the relationship between the degree of saturation (or water content) and suction at a constant temperature, which characterises the hydraulic behaviour of unsaturated soils, normally represented as the soil water retention curve (SWRC). The SWRC is commonly measured at nominal net stress by initially saturating a soil specimen and then subjecting it to drying and wetting paths, resulting in major drying and wetting curves. However, there is evidence that during these major drying and wetting paths and initial saturation, soil can undergo volumetric deformation with changes in void ratio, sometimes plastically. Therefore, for coupling the SWRC with mechanical behaviour, the dependency of SWRC on other state variables such as void ratio has been proposed. In this paper, an approach to defining SWRC for a particular plastic volumetric strain is presented within the generalised MPK model. The SWRC evolves as soil is subjected to wet/dry cycles, eventually approaching drying and wetting curves relevant to an environmentally-stabilised state. The performance of this model is demonstrated by the simulation of the loading/unloading/drying/wetting paths followed in a laboratory experiment. In addition, the evolution of the commonly-considered major drying and wetting curves is simulated, highlighting key features of the environmentally-stabilised line..

The Stress Triaxiality Effect under Large Plastic Deformation of a Polybutylene Terephthalate (PBT)

In this work, we focus on a new generation of polymer named Polybutylene terephthalate (PBT). In order to analyse and determine true behaviour of this polymer, a special experimental method was used. Hence, the true stress/strain responses are investigated under a large plastic deformation in different stress triaxiality frameworks with a particular attention on the volumetric strain evolution, with their decomposition to an elastic volumetric strain, plastic volumetric strain and the pure shear. Moreover, the effect of stress triaxiality on the plastic instability and the fracture strain is also examined. With the plastic instability analysis, it was found that plastic strain hardening increases gradually with the triaxiality. Finally, in order to evaluate the damage of this polymer, a theoretical damage formula is proposed.

THE BEHAVIOR CHARACTERISTICS OF A RESERVOIR LEVEE SUBJECTED TO INCREASING WATER LEVELS

Centrifugal model testing has been widely used to study the stability of levees. However, there have been a limited number of physical studies on levees where the velocity of increasing water levels was considered. To investigate the behavior characteristics of reservoir levees with different velocities of increasing water levels, centrifugal model tests and seepage-deformation coupled analyses were conducted. Through this study, it was confirmed that increasing water levels at higher velocities induces dramatic increases in the displacement, plastic volumetric strain and risk of hydraulic fracturing occurring in the core of the levee. Hence, real-time monitoring of the displacement and the pore water pres­sure of a levee is important to ensure levee stability.

3-D Poro-Elastoplastic Model for Short-Crested Wave-Induced Pore Pressures in a Porous Seabed

In this paper, a three-dimensional poro-elastoplastic model for the short-crested wave-induced pore pressures in a porous seabed is presented. Unlike the previous models, both elasticity and plasticity of seafloor are considered in the present model. This study considers the effects of wave and soil characteristics on the pore pressures and was validated with the previous wave experiment data. As the numerical analysis shows, higher value of plastic parameter leads to a faster residual pore pressure accumulation, which is closely related to the occurrence of seabed liquefaction. In particular, at the dissipation stage, residual pore pressure sharply decreases when enlarging plastic parameter , which dominates the velocity of accumulation of plastic volumetric strain.

Experimental Study on Evolution of Rock Damage Rule in the Condition of Conventional Three Axis Compression

Based on continuum damage mechanics, by defining the initial and critical damage value, because of the plastic volumetric strain of the specimen, we established the calculation methods of the rock specimen’s damage value. Through the conventional triaxial compression test of the shale, we find that damage value D changes as axial strain changes during compression, and summarizes its variation.

Effect of the Triaxiality in Plane Stress Conditions. Triaxiality Effect in a PVC Material

Polymer materials are gaining more and more importance in engineering applications. A new methodology of analysis is required in order to assess the capability of such material in withstanding complex loads. Therefore, the behavior of these materials currently arouses a great research interest. The use of PVC plastic pipes in pressure vessels and pipelines has increased rapidly in the last decade. In order to determine the plastic behavior of PVC, an experimental method is presented. Through the results obtained from experimental tests, in the first part of this paper, we investigate the use of a phenomenological model proposed by G’Sell and Jonas. The true stress-strain response under large plastic deformation was investigated in different stress triaxiality frameworks. Particular attention was given to volumetric strain evolution, separation resulting from elastic volumetric strain, plastic volumetric strain and pure shear. The effect of stress triaxiality on plastic instability and fracture strain was also examined. The deformation process should be considered as explained, and the anisotropic plastic response induced by the deformation could be introduced in constitutive equations of G’Sell.

Generalized Gradient-Dependent Plasticy Theory

Based on the Generalized Plastic Mechanics (GPM) and strain gradient-dependence of yield surfaces, the differential expressions of the volumetric and shear plastic strains are constructed, then the Generalized Gradient-dependent Plastic Mechanics (GGPM) is established to describe the strain localization characteristics and the basic mechanics characteristics of geo-materials. In order to discretize the controlling equations and the boundary conditions of analyses filed, an increment functional in which the displacement and plastic multipliers are independent variables was constructed to build up the variational principle of GGPM. Both the displacement and the plastical factor are discretized in space. A set of non-linear equations taking the displacements and the plastic factors of nodes as the unknown variables are obtained to solve the new proposed mechanic model. The boundary condition and the increment algorithm are also given. The numerical examples indicate that: (1) when strain localization appears,the plastic shear strain and the plastic volumetric strain mainly concentrate in localization band; (2) the mesh- dependency does not appear any more when the size of mesh changes; (3) when the parameters reflecting localization increase,the width of the strain localization band will be wider obviously.