Evaluation of the impact of pore fluid chemistry on the hydromechanical behaviour of clay-based sealing materials

Abstract

The results of an experimental program undertaken to evaluate the impact of pore fluid salinity on the hydromechanical performance of light and dense backfill materials are presented. Light and dense backfills are engineered barrier materials that are being examined in the Canadian concept for storage of spent fuel in a deep geological repository. The current research investigates the impact of pore fluid chemistry on the swelling, compressibility, stiffness, and hydraulic conductivity parameters of light and dense backfills that are required as material parameters for analysis and design. In these tests, pore fluid chemistry was selected to represent groundwater within potential host units including granite and limestone rock. Results show that the performance of light backfill is significantly affected by changes in pore fluid chemistry. The swell potential of light backfill decreases with increasing salinity of the solution. The hydraulic conductivity decreases with increasing effective montmorillonite dry density and specimens saturated with saline solution have higher hydraulic conductivity than those saturated with distilled water. Conversely, the behaviour of dense backfill is governed mainly by the crushed granite component and therefore changes to the pore fluid chemistry have relatively little effect. Results of dense backfill tests confirm the material performance as a sealing material.

Experimental study on the swelling behaviour of bentonite/claystone mixture

“…It has been observed that the effect of the chemistry of Bure site water on the swelling pressure is negligible. However, it is generally accepted that the swelling pressure decreases with the increase in salinity of the pore-water, although this decrease becomes less significant in case of high density (Karnland et al, 2005;Castellanos et al, 2008;Siddiqua et al, 2011;Komine et al, 2009). Castellanos et al (2008) reported that the swelling pressure of the FEBEX bentonite compacted to a dry density of 1.65 g/cm 3 decreases to almost half its initial value when 2 mol/L CaCl 2…”

“…The higher the initial dry density, the higher the swelling pressure or the higher the swelling strain; the swelling strain decreases with increasing initial water content, but the swelling pressure seems not to be affected by the initial water content (Komine et al, 1994;Villar et al, 2008). The swelling properties can be also affected by the chemical composition of the saturating fluid: the swelling capacity of the bentonite decreases with the increase in salinity of saturating fluid, although this influence becomes less significant for higher densities (Pusch, 1980;Sugita et al, 2003;Karnland et al, 2005;Castellanos et al, 2008;Siddiqua et al, 2011). Moreover, studies on the aging effects on the swelling behavior show that the swelling potential may decrease with time due to the rearrangement of clay particles with time (Nalzeny et al, 1967;Day et al, 1994;Subba Rao et al, 2003;Delage et al, 2006).…”

Squeezed Interstitial Water and Soil Properties in Pleistocene Blue Clays under Different Natural Environments

“…The alteration of the chemical properties of pore fluids (e.g., the change in the ion concentration or the cation valence, with the variation of dielectric constant by substitution of original pore fluids with other fluids), causes significant changes in the soil void index and, therefore, in the shear strength, compressibility and permeability of clays [4][5][6][7][8][9][10][11][12][13][14][15]. Sridharan and Venkatappa Rao [16] exploring the modified effective stress concept, highlight the two components of the clay volume change: the shearing resistance at inter-particle level controls the volume change in non-expanding lattice type clays like kaolinite, while diffuse double layer repulsive forces operate in the case of expanding lattice-type clays like montmorillonite.…”

Swelling pressure and hydraulic conductivity of compacted GMZ01 bentonite under salinization–desalinization cycle conditions

“…Compacted bentonite has been considered as buffer/backfill material for high-level radioactive waste (HLW) disposal in many countries (Pusch, 1983;Komine and Ogata, 1996;Villar, 2006;Siddiqua et al, 2011). Once it is emplaced, compacted bentonite is progressively hydrated by pore water infiltration from the host rock and can work as an effective barrier.…”