Effect of Unit Weight on Porosity and Consolidation Characteristics of Expansive Clays

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This study investigated the relationship between pore characteristics and unit weight of clayey soils. This relationship was particularly important in case of expansive soils, as the pore characteristics determine moisture flux boundaries, which in turn represent volume change behavior. Current research tried to evaluate the effect of compaction unit weight on the pore size and pore volume along with consolidation and swell characteristics on two expansive clays from semi-arid environment. The two selected clays represent soils with different degrees of expansion, particle size and mineralogy. Pore size characterization for these two soils was performed using Mercury Intrusion Porosimetry, while swell and consolidation characteristics were determined using a conventional oedometer test. Samples for both tests were compacted at different unit weights including, 100, 95, 90, 80, 75, and 70 % of maximum dry unit weight (MDUW) obtained from standard proctor. The compaction water content was kept constant for all unit weight levels. Both pore volume and pore size distribution was analyzed with varying unit weight characteristics and particle sizes. In addition, swell strains and compression indices were studied with varying unit weight of compacted specimens. It was observed that, in the case of samples compacted at 100 % MDUW, about 50 % of the pores were larger than 0.1 µm, and this value increased with reduction in unit weight. Current research is of practical importance, especially in the wake of microbial treatments for clayey soils where the passage of microbes depends on the pore size and more specifically pore throat size.