Impact of Physical Characteristics and Mineralogy of Clay on Swelling Behavior

Expansive soils, known for their considerable changes in volume resulting from moisture variations, present major challenges to geotechnical engineering, particularly in semi-arid environments. This study presents a detailed investigation into the geotechnical behavior, mineralogical composition, and morphological features of expansive soils sampled from a paddy field. Four subsurface samples (P1–P4) were extracted at a uniform depth of 1.3 meters. Post-collection, the samples were oven-dried and passed through a 0.425 mm sieve to standardize the material for testing. XRD analysis identified kaolinite, illite, quartz, and muscovite as dominant mineral constituents. XRF showed major components were silicon dioxide (51.93%), iron oxide (20.87%) and aluminum oxide (18.03%), indicating clay presence. SEM analysis revealed a porous microstructure with irregular, platy clay particles forming interconnected networks, affecting water absorption. Sample P3 exhibited the highest expansive potential, with a liquid limit of 64.61%, a plasticity index of 33.99%, and a free swell index of 17%. A low maximum dry density (1.175 g/cm³) and specific gravity (2.26) in P3 suggest a fine-grained matrix with a high proportion of clay minerals. P4 had high optimum moisture content (29%) due to silt-clay and coarse particles. Soils shrinkage 10.49-11.42% upon drying. Swelling potential varied from 10% (P2) to 17% (P3), likely due to differences in clay minerals. The findings underscore the role of mineralogy and moisture sensitivity in the swelling behavior of expansive soils and highlight the need for sustainable stabilization strategies employing environmentally benign additives.