Compacted swelling clays

ANALYSIS OF THE THMC BEHAVIOUR OF COMPACTED SWELLING CLAY FOR RADIOACTIVE WASTE ISOLATION... 

Compacted swelling clays are often envisaged as the main component of engineered barriers for radioactive waste disposal. These barriers are subjected to thermal loading due to the heat emitted by the waste and to hydration from water coming from the adjacent rock. As a consequence of these thermo-hydraulic phenomena, mechanical and chemical changes arise that, in turn, may affect all other aspects of behaviour. A correct understanding and prediction of these barriers would require, therefore, the performance of fully coupled thermohydro-mechanical and chemical (THMC) numerical analyses. 

Despite aggregation and compactness of clay lamellae in cyclohexane, the interlamellar space is not completely inaccessible, as styrene, even at small concentrations, may induce swelling. However, the hydrogenation rate may be limited by transport phenomena and diffusion control may develop. It is established that dL > 3 nm represents a sufficiently large distance between the clay lamellae for the reactants to enter the interlayer space and undergo hydrogenation there. 

Many of the lining materials commonly used for liquid storage cannot be used in salt gradient solar ponds. Compacted soils, native clays, soil additives or soil cement, swelling clays such as Bentonite, are not Impermeable to high temperature saturated salt brine solutions. Only the flexible membrane lining materials offer the potential for impermeability (zero leakage)... 

The preparation of buffer clay is made by compaction of dry clay powder to blocks with a high density. The blocks are then placed in the deposition holes to surround the containers. Very dense blocks of highly compacted smectitic clay powder are placed around the containers, embedding them tightly. The required tightness is attained when the clay material swells after taking up water from the surrounding rock. 

The determination of the swelling pressure as a function of temperature in the interval between 25 and 80 °C has been performed in the oedometers shown in Figure 2. The clay has been uniaxially compacted with its hygroscopic water content at initial dry densities of 1.50 and 1.60 g/cm . Vertical stresses of 11 and 16 MPa, respectively, were applied to obtain specimens of 5.0 diameter and 1.2 cm height. 

Nishimura, T. 2001. Swelling pressure of a compacted bentonite subjected to high suction, pages 109-114. Clay Science for Engineering, Proceedings of the international symposium on suction, swelling, permeability and structure of clays - Is-Shizuoka. Balkema, Rotterdam. 

Mixtures of naturally deposited sand, medium plasticity clay, and bentonite with recycled rubber produced composite materials suitable for use in ground improvement (Becker and Vrettos, 2011). Mechanical properties of soils relevant to the application of such composites in geotechnical engineering problems were investigated. The compaction, permeability, compressibility, and flexural and shear strength were determined for typical mixtures along swelling of the bentonite-mbber mixtures. 

Bentonite and the other clay minerals have considerable ion exchange capability, and their physical characteristics change dramatically depending upon the content of the salt solution in their pore space, and whether the clay is in the calcium or sodium form. As examples of publications considering the influence of calcium chloride on clays Sjoblom et al. (1999) noted the slowness of water to penetrate compacted bentonite (Na-montmorillonite is its major constituent), but that a calcium chloride solution could rapidly penetrate the bentonite and allow it to be washed away. Fresh water causes compacted bentonite to swell and to produce free-surface particles by exfoliation. These particles form a gel which further closes the pores to water uptake, while the CaCl2 solution causes the exfoliated material to shrink (or at least swell less). This allows more solution to enter the pores, causing differential expansion and a lower gel strength so that the clay may be more easily washed away. 

Dennis, J. H. (1991). Compaction and Swelling of Ca-Smectite in Water and CaClj Solutions. Clays, Clay Miner. 39(1), 35-42. 

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