Influence of aggregate structure on the compressibility of an unsaturated compacted silty sand

Abstract

It is well recognised that the compressibility of unsaturated soils is affected by soil structure. However, the effects of soil aggregation and pore structure on the compressibility behaviour of unsaturated soil are still not well understood. In this study, the effects of soil aggregation and pore structure on the compressibility of unsaturated silty sand were investigated. Specimens were purposely prepared at two compaction water contents to similar void ratios. They were saturated after compaction and dried to suction values of 0, 50, 150, or 300 kPa following a similar hydraulic loading path, after which they were subjected to isotropic loading and unloading. Mercury intrusion porosimetry (MIP) and micro-X-ray computed tomography (μ-XCT) were used for microstructural studies. At a given suction, specimens compacted on the dry side are less aggregated (smaller aggregate sizes) showing higher compressibility, whiles specimens compacted on the wet side are highly aggregated (larger aggregate sizes) revealing lower compressibility. The low compressibility of the highly aggregated soil is attributed to the additional drying-induced intra-aggregate strength due to the suction stiffening effects from meniscus water within the aggregates.