Aquifer protection: a combined study of microstructure and transport properties in clay-sand mixtures

The study focuses on the analysis of the effects of swell-shrinkage potentials on the microstructure of bentonite-sand mixtures, to gain insight into changes with varying hydration states, performed by field emission scanning electron microscopy (FESEM) and Nuclear Magnetic Resonance (NMR). In addition, permeability experiments on similar artificial soils were undertaken in oedometric conditions, by means of a constant head permeameter, to validate the suitability of the soil for the construction of liners in landfills, for the purpose of aquifer protection. FESEM observations indicate microstructural changes with dehydration that involve reorientation of the tactoids and closure of micropores. As to permeability tests on the mixtures, the results showed that the addition of very small percentages of clay induces variations of more than three orders of magnitude. Following the results, a discussion highlights the suitability of the Revil and Cathles (1999) model, using NMR and permeability tests.