Yasuaki Ichikawa

In situ X-ray diffraction observation of smectite hydration under constant volume

Smectite (especially, montmorillonite) is the major clay mineral constituent of bentonite, which is designed to play a key role as a buffer material in geological repositories for the final disposal of radioactive waste in Japan. It is therefore crucial to understand the hydration behavior of smectite in terms of swelling during hydration and saturation processes. Against such a background, the authors simultaneously observed behaviors of smectite swelling at the micro-level (i.e., both the generation of swelling pressure and the change of hydration state). In the experiments, deionized water was allowed to permeate into a dried specimen of smectite (named Kunipia-F®) with different dry densities (ρd: 0.97, 1.23, 1.43, 1.64 and 1.88 Mg/m3) under conditions of constant temperature and volume. The swelling pressure was measured using an in situ uniaxial consolidation apparatus during the water feeding process. Changes in local hydration states (i.e., one-molecular-layer hydration states to three-molecular-layer hydration states) were also simultaneously observed. Hydration among these different states propagated from the inlet side to the outlet side of the specimen. The authors discussed the relationships governing the hydration state, swelling pressure, the number of hydration moles, dry density, equilibrium final pressure, and then the dynamic mechanism behind pressure propagation.

Homogenization Analysis of Diffusion in Porous Media

We examine the problem of diffusion in a porous medium using a homogenization analysis (HA). Diffusion problems have important applications in environmental geosciences. We clarify the mechanism of diffusion, convective transport and adsorption in porous media at both the microscale and macroscale levels. Attention is particularly focused on diffusion processes in bentonite, which is an engineered geological barrier to be used to buffer the transport of radionuclides from deep geologic repositories.

Classical Theory of Diffusion and Seepage Problems in Porous Media

In this chapter we develop the coupled diffusion and seepage problem using the theory of mixtures. It is clearly understood that the diffusion problem is strongly linked to the seepage problem through the mass conservation law. Adsorption on the solid surface is treated using the concept of an ‘adsorption isotherm’.

Calculation of Permeability of Clay Mineral in Natural Slope by Using Numerical Analysis

A natural landslide is mainly occurred by rainfall, snowmelt, earthquakes and construction works. Especially, the role of rainfall or snowmelt in slope stability is very important because it causes a decrease in shear strength by reducing the soil cohesion. If clay exists in the weathered soil, the physical characteristics such as viscosity and permeability are generally different from the condition without the clay. In this case, changes of permeability or viscosity due to the rainfall or snowmelt are dependent on the content of clay in soil. In order to calculate the variation in permeability according to the content of clay in soil, many researchers have conducted laboratory experiments or in-situ tests in the field. However, it is difficult to determine the property of the clay such as a viscosity because of its poor crystalline property. In order to solve this problem and to calculate permeability of clay under various dry densities, we used molecular dynamic (MD) simulation to examine the viscosity of micro scale and homogenization analysis (HA) method to expand micro material property to macro scale. In this research, we determined the permeability of clay with various dry densities due to the rainfall or snowmelt conditions by using MD/HA method.

Introduction to Homogenization Analysis

We outline the essential features of a multiscale homogenization analysis. A problem of a one-dimensional elastic bar is given as an example.

Non-equilibrium Thermodynamics

We first review the principles of Classical Thermodynamics (see also Appendix D), and proceed to give an alternative formulation of Thermodynamics in the context of a true dynamical process.

Introduction to Continuum Mechanics

The mechanics of a deformable body treated here is based on Newton’s laws of motion and the laws of thermodynamics.

Homogenization Analysis and Permeability of Porous Media

The Navier-Stokes’ (NS) equations can be used to describe problems of fluid flow. Since these equations are scale-independent, flow in the microscale structure of a porous medium can also be described by a NS field. If the velocity on a solid surface is assumed to be null, the velocity field of a porous medium problem with a small pore size rapidly decreases (see Sect.5.3.2). We describe this flow field by omitting the convective term \(\mathbf{v} \cdot \nabla \mathbf{v}\), which gives rise to the classical Stokes’ equation. We recall that Darcy’s theory is usually applied to describe seepage in a porous medium, where the scale of the solid skeleton does not enter the formulation as an explicit parameter. The scale effect of a solid phase is implicitly included in the permeability coefficient, which is specified through experiments. It should be noted that Kozeny-Carman’s formula (5.88) involves a parameter of the solid particle; however, it is not applicable to a geometrical structure at the local pore scale.

Classical Theory of Consolidation for Saturated Porous Media

Soil is a mixture of a solid phase, a liquid phase (i.e., water) and a gaseous phase. Saturated soil is a two-phase material which consists of a solid phase and a liquid phase. The formulation of a theory for a saturated soil commenced with the concept of the effective stress of Terzaghi at the beginning of the twentieth century, and Terzaghi’s concept was extended by Biot to a three dimensional consolidation theory.

Long-Term Consolidation of Bentonite and a Homogenization Analysis of the Flow Field

Proposals for the geological disposal of heat emitting high-level radioactive wastes (HLW) have been put forward by many countries including Japan, Canada, Sweden, Switzerland, USA, Spain and others. The disposal concepts invariably involve underground multi-barrier schemes where bentonite clay is chosen for a number of desirable attributes including its swelling potential and ability to trap the majority of released radionuclides (JNC 1999; Chapman and McCombie 2003).