Micromechanical study of clay stabilized with nano-Al2O3 particles and reinforced by polypropylene short micro-fibers

• Nano alumina and polypropylene fibers greatly improved clay strength and stiffness. • A micromechanical model accurately predicted stiffness of treated clay samples. • Combined additives created denser structure and reduced brittleness in clay soils. • Model predictions closely matched results from laboratory compression tests. Understanding the geomechanical behavior of clayey soils is essential in geotechnical engineering. This study investigates the combined effects of nano-Al 2 O 3 particles and polypropylene (PP) short micro-fibers on clay through laboratory testing and micromechanical modeling. A hierarchical micromechanics-based model is proposed to predict the effective stiffness of nano-Al 2 O 3 /PP/clay ternary composites, explicitly incorporating microstructural parameters such as filler content, geometry, and interfacial bonding. The model accounts for the PP–clay interfacial region, nanoparticle dispersion, fiber waviness, and orientation. Clay samples were stabilized with 0–1 % nano-Al 2 O 3 and 0–1.2 % PP fibers by dry weight, and unconfined compression tests were conducted to determine unconfined compressive strength (UCS) and stiffness (E 50 ). At 1.2 % PP fiber content, increasing nano-Al 2 O 3 improved UCS by up to 78 % and E 50 by up to 142 %. Likewise, PP fibers enhanced UCS by 76 % and E 50 by 57.5 %. SEM analysis revealed nanoparticle-induced particle interlocking and fiber-enhanced cohesion, while EDS confirmed the integration of Al and C elements into the soil matrix. Experimental results showed strong agreement with model predictions, validating the proposed approach. This micromechanical framework provides an effective predictive tool for optimizing fiber- and nano-modified clays, contributing to more efficient and sustainable soil stabilization practices.