The effect of sand gradation on the hydro-mechanical characteristics of sand-bentonite mixtures as buffer material

ABSTRACT: Municipal solid waste produces gas, heat and leachate in landfill repository systems. In radioactive waste disposals, radionuclide wastes raise the temperature around the containers as well as applying high pressures on waste barriers which create mechanical stresses that have made them subject to research for determination of hydro-mechanical properties, which are as essential as the thermal properties. In this thesis, the findings of a study on hydro-mechanical characteristics of compacted sand-bentonite mixtures are presented, which are among the materials recommended to be used as hazardous waste container and barrier materials for landfills as a liner. Mixtures of bentonite with two different types of sand in two different proportions of bentonite (15%-25%) have been studied. The experimental work achieved to assess the characteristics of these mixtures consists of compaction tests, unconfined compression tests, one-dimensional swell-consolidation tests, shrinkage tests and determination of soil-water characteristic curves by suction measurements. The experimental data obtained in this research study conclude that with increasing bentonite content in mixtures, swelling pressures increased and cracking appeared in samples upon shrinkage, which made the structures unstable. On the other hand saturated hydraulic conductivity and unconfined compressive strength characteristics of mixtures were improved. The changes in hydro-mechanical performance due to various specimen combinations were considered and discussed based on the suction components of soil mixture. At the end, it was concluded that the compacted crushed limestone sand-bentonite mixture with 15% bentonite content could be a feasible mixture in waste containers as a buffer material which can be considered in future. …………………………………………………………………………………………………………………………………………………………………………………………………………