An experimental and numerical investigation to evaluate geotechnical properties of fox nutshell ash amended black cotton soil

Expansive soils pose serious challenges in geotechnical engineering due to their high compressibility, swelling potential, and low strength, which adversely affect the stability of structures, particularly foundations. At the same time, the increasing generation of agricultural waste creates environmental concerns and disposal issues. Utilizing agricultural waste materials such as Fox Nutshell Ash (FNA) as stabilizers offers a sustainable solution to both problems. Hence, the present study investigates the geotechnical behaviour BC soil with varying FNA contents of 0%, 5%, 8%, and 10%, and its index properties, compaction characteristics, strength, swelling behavior, consolidation, and compressibility were evaluated using standard laboratory tests. The results indicate that FNA reduces plasticity, swelling potential, free swell index and also enhancing UCS values by 75% at 5% FNA and 73% at 8% FNA after 28 days of curing. Consolidation behavior improved with an increase in C v of up to about 31% and a significant reduction in compressibility parameters, indicating better drainage and reduced volumetric deformation. The shear strength response showed an increase in cohesion at 5% FNA and an improvement in friction angle at 8% FNA, indicating a shift toward friction-governed behavioravior of Black Cotton (BC) soil through laboratory experiments and numerical analysis. The Numerical modelling results also indicated a consistent improvement in ultimate bearing capacity by approximately 15–19% with FNA inclusion, along with a favorable settlement response at higher FNA content. Therefore, the findings suggest that FNA in the range of 5–8% is optimal for enhancing the strength, consolidation, and foundation performance of BC soil, highlighting its potential as a sustainable and cost-effective stabilizing material for geotechnical applications.