Abstract
Fine grain soils have a complex engineering behaviour which depends but not limited to moisture content, changes in external pressure and characteristics of the pore medium. Sand often contains a considerable percent of silt which is expected to alter its natural behaviour. This composite matrix is referred to as silty-sand. To understand the behaviour of this matrix under varying moisture conditions, some of the factors influencing the soil-water characteristics of unsaturated silty sands were investigated. Representative samples were collected from a river bank after its index properties were predetermined in the laboratory. The samples were compacted at different moisture conditions and compactive efforts. With the pressure plate extractor device, the Soil-Water Characteristic (SWC) was obtained and SWC Curves plotted. Compaction at greater compactive effort (modified proctor) and optimum moisture content produced the largest air entry value and reduced air voids. The air entry values of the soils obtained ranged from 21 kPa to 57 kPa. Also changes in the shape of the SWCC were consistent with changes in pore size which occur by varying compaction conditions. Result shows that soil structure, compaction water content, compactive effort and percentage of fine particles are factors affecting the Soil-Water Characteristics.
Highlights
Silty sand is considered a delicate composite matrix containing a sand-grain-matrix and a silt-matrix
Changes in the shape of the Soil-Water Characteristics Curve (SWCC) were consistent with changes in pore size which occur by varying compaction conditions
Result shows that soil structure, compaction water content, compactive effort and percentage of fine particles are factors affecting the Soil-Water Characteristics
Summary
Silty sand is considered a delicate composite matrix containing a sand-grain-matrix and a silt-matrix. Tern (1977) are said to consist of a four-phase system: soil particles, pore air, pore water and a contractile skin. These soils are found most especially in the arid and semi arid regions where the ground water table is at a considerably great depth beneath the ground surface, such as the tropical regions. Natural, desiccated and compacted soils are few examples that fall into this category. They are known to possess negative pore water pressures and are susceptible to expansion and shrinkage. Compacted natural soils used as hydraulic barriers in waste containment facilities such as engineered landfills are often unsaturated and modelling of flow and transport through these soils requires the knowledge of their unsaturated hydraulic properties
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