Properties Of Compacted Bentonite Research Articles

Evaluation of direct shear strength of compacted bentonite having pore-water pressure

Safety of great deep repository design has been investigated for high-level radioactive waste disposal system in several countries such as Belgium, Canada, China, France, Germany, Japan, Sweden and Switzerland. The repository of the disposal is in most cases based on the concept of a multi-barrier system using the host rock barrier formation and a man-made barrier formation. The man-made barrier consists of high expansive bentonite. Thermal-hydro-mechanical behaviour simulation models were developed, including some parameters described by experimental works. The complex phenomena due to the transition into saturation and chemical reactions at the bentonite barrier system have been explained. This study focused on direct shear strength for compacted bentonite related to some factors induced by uncertainty problems such as hydration effect and pore-water pressure. Measured shear strength properties of compacted bentonite had been determined at high suction values. Also, it is clear that there is some influence of direct shear speed on direct shear strength both under unsaturated-saturated conditions. A modified direct shear apparatus was used in this study to observe changes in shear strength with increments of pore-water pressures.

Effects of K+ solutions on swelling behavior of compacted GMZ bentonite

During the long-term operation of a deep geological repository, the buffer/backfill properties of compacted bentonite could be affected by the chemistry of the infiltrated porewater. In this study, swelling tests and microstructural analyses were conducted on the compacted GMZ bentonite specimens with an initial dry density of 1.5 or 1.7 Mg/m3 with infiltration of distilled water, as well as, KCl and KOH solutions (0.1 and 1.0 M). Influences of K+ solutions on the swelling behavior of compacted GMZ bentonite were investigated. Results show that swelling properties of compacted GMZ bentonite specimens could be significantly influenced by concentration of K+ solutions and dry density of specimens. Swelling pressure of compacted GMZ bentonite specimens was significantly attenuated by infiltration of K+ salt/alkaline solutions. For swelling strain tests with infiltration of KCl or KOH solutions, instead of a secondary swelling stage, a volumetric collapse stage was observed. Micro-structural test results demonstrate that the attenuation of swelling behavior could be attributed to the K+ exchange or silica dissolution.

Influence of salt solutions on the swelling pressure and hydraulic conductivity of compacted GMZ01 bentonite

During the long-term operation of a deep geological repository, infiltration of groundwater with different chemical compositions can affect the buffer/backfill properties of compacted bentonite. Using a newly developed apparatus, swelling pressure and permeability tests were carried out on densely compacted GMZ01 bentonite samples, which has an initial dry density of 1.70Mg/m3, with de-ionized water as well as NaCl and CaCl2 solutions at different concentrations. Salinity effects of infiltrating solutions on swelling pressure and hydraulic conductivity of tested samples were investigated. Results obtained show that the swelling pressure of GMZ01 bentonite decreases with increasing concentration of infiltrating solutions, while the degree of the impact decreases with the increase of concentrations. Moreover, swelling pressure reaches stability more rapidly in case of high concentrations. The hydraulic conductivity of GMZ01 bentonite increases with the increase of solution concentrations. Comparison shows that the impact of NaCl solutions on the swelling pressure and hydraulic conductivity is higher than that of CaCl2 solutions at same concentrations. This may be explained by the impact of cation types on the microstructure of bentonite.