Swelling bentonite barriers

Figure 10 presents simulated and measured evolution of stress normal to the drift wall at two locations (E2G2 and B2G in Figure 9). The simulated stress began to develop as soon as the wetting commenced and increased to about 2 to 2.5 MPa at 1,000 days. The measured stress indicates that the swelling stress might not have begun to develop until several months after heater tum-on. This delay in the development of swelling stress was a common observation at many monitoring points in the bentonite barrier at FEBEX.

The evolution of stress in the bentonite barrier at FEBEX was affected by the existence of gaps between the pre-fabricated bentonite blocks. The swelling pressure did not develop until moisture swelling of the bentoninte blocks had closed the gaps completely. 

Based on the characterization of the rock massif and on the details of the process of test installation and performance, the rock response in the immediate vicinity of the buffer was required. The rock is now subjected to the heat released by heaters and to swelling pressures resulting from bentonite hydration. The initial hydrological regime (Part A) is also modified by the presence of the impervious barrier. Temperature, stresses, water pressures and displacements in selected points of the rock were required. 

This paper will focus on the hydraulic properties of the swelling materials, especially on the bentonite that is used in the Full-scale Engineered Barrieres Experiment in Crystalline Rock (FEBEX). The influence of swelling will be shown in a simulated laboratory experiment and in the application on the FEBEX in situ experiment. 

Bbrgesson, L. 1984. Water flow and swelling pressure in non-saturated bentonite-based clay barriers. In Clay Barriers for Isolation of Toxic Waste Proc. Intern. Symp., Stockholm, Sweden, 28-30 May 1984. 

Buffer material for high-level waste disposal is expected as a barrier with groundwater preventive ability, self-sealing ability, adsorption ability, etc. As a buffer material, bentonite has attracted attention because its swelling characteristics are useful for sealing the initial cracks within the buffer material or the initial gaps between the buffer material and the surrounding rock. 

The group of Gu Z. in the 2009, reported the behavior of styrene butadiene/ rubber/organo-bentonite nanocomposite prepared from latex dispersion, content was lower than 12 mass%. The results showed were that presence of organo-bentonite in the nanocoposite affects direct in the thermo stability, mechanical properties and swelling behavior, which was attribute to the good barrier properties of the dispersed nanoparticles. The dispersion is an important factor that can affect various properties such as thermal stability [81]. 

Proposals for the geological disposal of heat emitting high-level radioactive wastes (HLW) have been put forward by many countries including Japan, Canada, Sweden, Switzeriand, 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). 

Geotextile—bentonite composites are well known as GCLs. They are excellent water-barrier materials. However, a disadvantage of GCLs is that it has an increase in hydraulic conductivity in sea water owing to the swelling mechanism of bentonite. This section introduces how to improve the swelling behavior by modification (Table 18.1). 

Here poly(ethyl aerylate) (PEA)/clay nanocompsite as the first example of rubbery polymer/elay nanocomposite synthesized by in situ emulsion polymerization is reported. The clay used is bentonite having extremely strong swelling characteristies in water. The resulting nanocomposite emulsion is directly cast to form film without coagulation process. This study focuses on microstructure, thermal and meehanical properties, and gas barrier permeability of the final PEA/clay nanoeomposites. 

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