Role of Physico chemical Processes And Micro structural Features in Influencing Moisture Loss and Engineering Properties Of Compacted Residual Soils Exposed To Environmental Relative Humidity

Abstract

The moisture content of residual soils above the water table, and near ground surface (and#8804; 6 m) is influenced by the environmental relative humidity (RH). The focus of this thesis is to examine the physico-chemical and physical mechanisms of moisture retention and moisture loss in unsaturated residual soils in response to environmental RH and the implications of such changes on the engineering behavior of soils. The physicochemical drivers of moisture retention include forces and energy responsible for adsorption and desorption of water molecules on soil particle surfaces and capillaries, while the micro-structural features include, tortuosity and pore structure in influencing moisture retention and transport in unsaturated soils. In this study, laboratory experiments were performed with representative fraction of residual soil collected from Indian Institute of Science Campus, Bengaluru and five different saturated salt solutions were used to maintain environmental RH of 97%, 76%, 64.4%, 33% and 7% in the desiccators. The thermodynamics of moisture loss from the residual soil specimens were explored by performing experiments with moist powder soil specimens that were exposed to environmental RH of 33 to 97% at various constant temperatures (16 to 35°C). Distribution constant (Kc) is employed to account for the affinity of desorption of water molecules from soil particles. Analysis of laboratory results revealed that moisture desorption is an endothermic process associated with positive entropy changes and the trend of and#916;Go (free energy change) variations indicated that moisture desorption is most favored at low environmental RH. Similar to SWRC (soil water retention curves), the ability of GAB (Guggenheim- Anderson-de Boer) isotherm to characterize the equilibrium soil moisture content - RH relations of compacted residual soil specimens along the drying path were explored and was successful in predicting the equilibrium water contents inspite of the variations in initial compaction conditions...