Pore structure effects on the water retention behaviour of a compacted silty sand soil subjected to drying-wetting cycles

Abstract

Most of the previous studies on the effects of pore structure on soil water retention behaviour are limited to a single drying and wetting cycle. This study evaluated the effects of pore structure on water retention behaviour for specimens prepared at different pore structures of similar density, subjected to drying-wetting cycles. Specimens were compacted at two density states equivalent to loosely compacted fill slopes (80% relative compaction, e = 0.78), and densely compacted slopes or subgrade compaction specifications (95% relative compaction, e = 0.50) at different water contents on the wet side (20%) and dry side (10%) of the optimum water content. The results show that loosely compacted specimens prepared on the wet side have a lower water retention ability due to the larger formed macropores. They also show a significantly higher degree of hysteresis which decreases with drying and wetting cycles. For loosely compacted specimens, there is a higher increase in water retention ability with cycles for specimens prepared on the dry side, due to more drying and wetting-induced pore evolution and volumetric changes. Increasing compaction density results in a higher water retention ability but reduces the number of cycles needed to achieve water retention equilibrium with drying-wetting cycles, subsequently behaving as scanning curves. This is attributed to the less pore evolution and smaller volumetric strain at lower void ratios. Pore structure effects on water retention behaviour subjected to drying-wetting cycles should be considered in civil engineering designs for earth structures, such as loosely compacted fill materials.