Shintaro Ohno

Elasto-Plastic Constitutive Model for Unsaturated Soils with Subloading Surface Concept

An elasto-plastic constitutive model for unsaturated soils is improved to realize numerical stability of computations at the singular point on the yield surface and an accurate prediction of the mechanical behavior of overconsolidated (or elastic state) soils in this chapter. The authors introduce the exponential contractancy model (EC model) by Ohno et al. (J Appl Mech JSCE 9:407–414, 2006) and the subloading surface model by Hashiguchi and Chen (Int J Numer Anal Method Geomech 22:197–227, 1998) to the elasto-plastic constitutive model for unsaturated soils by Ohno et al. (J JSCE 63(4):1132–1141, 2007). The applicability of the constitutive model is verified by simulating triaxial shear tests under constant net stress undrained conditions.

A Numerical Interpretation of Density Homogenization of Bentonite Material in Wetting Process

Due to its low permeability and excellent expansion characteristics, bentonite is an excellent candidate with potential use as a buffer in the disposal of nuclear waste. Its expansion characteristics, activated by wetting, can be interpreted based on the full saturation line, depicted as a unique line on the density and the confining pressure relationship as proposed by Kobayashi et al. (2007). In addition, its elasto-plastic constitutive relation can also be formulated by introducing additional irreversible strain component describing the expansion of the montmorillonite present in the bentonite material. A constitutive model can consistently express the mechanical behavior of the compacted bentonite material from the unsaturated to the fully saturated state. This paper describes the density homogenization process that was conducted through a series of soil-water coupled elasto-plastic finite element simulations. Specifically, bentonite specimens, with different initial densities, were permeated with a constant water head. Stresses and strains developing in bentonite, particularly the density change, were carefully examined. A series of numerical simulations, performed on the two specimens, showed that specimens did not homogenize to a unique value of density upon reaching the fully saturated state. To confirm the simulation results, we carried out a series of experiments. The experimental results also support our simulation results.Copyright