Volume change behaviour of clays: the influence of mineral composition, pore fluid composition and stress state

High stress consolidation tests (up to 30 MPa) were carried out on slurries made up of three bentonites considered as possible constituents for engineered clay barriers used for nuclear waste disposal at great depth (Na Kunigel, Na-Ca MX80 Wyoming clay, and Ca Fourges clay). Water retention curves (WRCs) were determined for a wide range of suctions (up to 305 MPa). A bilinear shape for the compression curves and the WRCs was observed in the three clays, with significant changes occurring in the 0.41 MPa suctionstress range. The permeability and the coefficient of consolidation were also determined during the compression tests. In the WRCs and compression curves, the two clays containing Na+ exhibited a similar behaviour, which was different from that of the Ca2+ clay. The coefficient of consolidation for the three clays was decreasing in the 0.41 MPa stress range and increasing at higher stresses. Data were interpreted in the light of existing experimental observations on the microstructural changes of...

On the high stress compression of bentonites

Influence of pore water chemistry on the swelling behavior of compacted clays

In this study, the effects of salinity of infiltrating solutions on the swelling strain, compressibility, and hydraulic conductivity of compacted GMZ01 Bentonite were investigated. After swelling under vertical load using either distilled water or NaCl solutions with concentrations of 0.1, 0.5 M, and 1 M, laboratory oedometer tests were conducted on the compacted GMZ01 Bentonite. Based on the oedometer test results, hydraulic conductivity was determined using the Casagrande’s method. Results show that the swelling strain of highly compacted GMZ01 Bentonite decreases as the concentration of NaCl solution increases. The compression index C
 c
 *
 increases and then turns to decrease with an increase in the vertical stress or a decrease in the void ratio for different solutions, and the C
 c
 *
 decreases as the concentration of NaCl solution increases. The secondary consolidation coefficient C
 α increases linearly with the increase of the compression index C
 c
 *
 . Furthermore, a bi-linear relationship between the swelling index C
 s
 *
 and the secondary consolidation coefficient C
 α can be characterized clearly. The hydraulic conductivity increases as the concentration of NaCl solution increases, however, this increase can be prevented if a high confining stress is applied.

Effects of salt solutions on the hydro-mechanical behavior of compacted GMZ01 Bentonite

Compressibility behaviour of lime-treated marine clay

L'on etudie les effets du systeme argile-eau-electrolyte, et de la temperature sur la compressibilite du sol due a la consolidation primaire et la compression secondaire. La methode utilisee pour l'alteration du complexe d'echange a fourni une seule espece de cation (Na + , Ca ++ , ou K + ) pour dominer le complexe d'echange, soit plus de 87% du total des cations echangeables presents dans le complexe d'echange. Le complexe d'echange domine par le potassium (K + ) a produit des changements fondamentaux dans le comportement du sol teste: par rapport au sol non traite, le sol traite au potassium a subi une diminution de 66 a 13% de I p , de 10,5 a 1,7% du gonflement libre, et une augmentation par un facteur 10 du coefficient de permeabilite. L'on trouve que l'indice de compression vierge (C c ) est fortement relie au poids volumique sec du sol et peut etre modelise en consequence avec precision. La temperature affecte de facon significative le comportement du sol non traite; le coefficient de permeabilite mesure a ete augmente d'environ 100% pour un changement de temperature de 26 a 40°C, alors que la temperature n'a quasiment pas d'influence sur le sol traite au potassium.

M S Al-Zou'bi

Papers

On the physicochemical aspects of compacted clay compressibility