Investigating the synergistic effects in hybrid sustainable soil stabilization using rice husk ash and basalt mesh on compaction and shear strength development

Sustainable ground improvement aims to use industrial and agricultural byproducts. Rice husk ash (RHA), a high-silica agricultural waste, can act as a pozzolanic soil stabiliser, while basalt fibre mesh (a natural, high-strength geotextile) can reinforce soil. This study assesses the combined effect of RHA and basalt mesh on the strength of compacted soil. Laboratory compaction and consolidated-drained triaxial compression tests were performed on silty sand mixed with 0–15% RHA by weight. Basalt fibre meshes of two aperture sizes (5 mm and 10 mm) were embedded at the top, middle, or bottom layers of the specimens. Adding RHA progressively reduced maximum dry density (from 1.79 to 1.09 g/cm³ as RHA increased from 0% to 15%) and increased optimal moisture (from approximately 15.7% to 27.1%). In triaxial shear tests, RHA-modified soils showed increased internal friction angles with variable effects on cohesion depending on dosage compared untreated soil. For example, untreated soil had φ ≈ 11.5° and c ≈ 78 kN/m², whereas a 10% RHA mix without mesh reached φ ≈ 19–20°. Embedding basalt mesh significantly increased cohesion: the soil without RHA but reinforced with mesh had c ≈ 147 kN/m². The combined RHA–mesh systems exhibited response dependent on both material dosage and reinforcement placement. The highest measured friction angle was observed for 10% RHA with the 10 mm basalt mesh placed at mid-depth, achieving φ ≈ 23.7° (almost double the control) though with reduced c ≈ 40 kN/m². These results indicate a trade-off between frictional resistance and apparent cohesion depending on the treatment configuration. Based on the experimental results within the tested range, the combination of approximately 10% RHA with mid-depth basalt mesh provided the most favourable balance of shear strength parameters under the present conditions. This has implications for sustainable infrastructure, demonstrating that recycled agricultural waste and natural fibre geotextiles can jointly improve weak soils without reliance on high cement contents.