Strength and Consolidation Characteristics of Expansive Clay Improved with Lime–Nano-Metakaolin and Sisal Fibre Reinforcement

Expansive clay soils are known for their low strength and high compressibility, which often lead to severe geotechnical challenges in construction. This study evaluates the combined effects of lime, nano-metakaolin (NMK), and sisal fibre on the strength and consolidation behavior of expansive clay. Lime content was maintained at 4%, while NMK was varied at 4, 8, and 12%, and sisal fibre was incorporated at 2, 3, 4, and 5% by dry weight of soil. A series of laboratory tests, including unconfined compressive strength (UCS) and one-dimensional consolidation tests, were conducted to determine the mechanical and compressibility characteristics of the treated soils. The results indicate that the inclusion of NMK significantly enhanced pozzolanic reactivity with lime, leading to improved soil bonding and higher UCS values. The addition of sisal fibre provided tensile bridging within the soil matrix, which increased ductility and contributed to sustained strength at higher fibre dosages. In terms of consolidation, the treated specimens showed reduced compressibility and lower coefficient of consolidation compared with untreated expansive clay, reflecting the densification and pore-filling effects of lime–NMK reactions and fibre interlocking. The optimum performance was observed at intermediate NMK contents (8%) and fibre reinforcement of 3–4%, where a balance between strength gain and reduced compressibility was achieved. Overall, the study demonstrates that a combination of lime, NMK, and sisal fibre provides a sustainable and effective technique for improving the strength and consolidation properties of expansive soils, with promising applications in geotechnical engineering practice