Influence of Matric and Osmotic Suction on the Collapse Potential of Semi-Arid Loess in Western India

Collapsible loess deposits in semi-arid regions present significant geotechnical challenges due to their sensitivity to moisture fluctuations. This study investigates the hydro-mechanical behavior of loess soil from Chandwaji, Rajasthan, by characterizing its suction properties across a range of moisture contents from dry-of-optimum (OMC-4%) to wet-of-optimum (OMC+4%). Using the filter paper method (ASTM D5298-10), both total and matric suction were measured to decouple the contributions of capillary and osmotic forces to the soil’s stability. The results demonstrate a profound reduction in soil energy potential upon wetting: Total suction decreased from 2,287 kPa at OMC-4% to 22.2 kPa at OMC+4%. A critical transition was observed at the OMC-2% state, where matric suction dropped sharply to 116 kPa while total suction remained high at 903 kPa, revealing that osmotic suction (787 kPa) becomes the dominant stabilizing force (87% contribution) in this transition zone. This finding suggests that the collapse mechanism in semi-arid loess is driven not only by the loss of capillary tension but also significantly by the dissolution of soluble salts. The study highlights the necessity of accounting for both suction components in settlement prediction models, as neglecting the osmotic component may underestimate the collapse potential of soils in arid environments.