Experimental Study on Expansive Soil Stabilization Using Biostimulation and Recycled Sanitary Napkin Fiber Reinforcement

Expansive soils undergo significant volumetric changes with moisture fluctuations, posing challenges to infrastructure durability. Sanitary napkin disposal is one of the biggest issues, because it poses soil and water pollution due to its nonbiodegradable nature and air pollution because of disposal via incineration. Moreover, according to the recently developed technology by PadCare Labs, India, sanitary napkins can be converted into colorless, odorless, and sterilized plastic fibers. This study introduces a novel technique that utilizes the biostimulated microbially induced calcite precipitation (MICP) method and incorporates recycled sanitary napkin fibers (SNFs) for the stabilization of expansive soils and reduction of swelling. Integration of SNF into soil offers dual benefits: reinforcement and waste reduction. In the present study, native soil bacteria were stimulated to induce calcite precipitation, enhancing bonding, while SNFs improved crack resistance and tensile strength. Experimental work was conducted on expansive soil treated with varying SNF contents (0.25%–1%) and subjected to MICP after 2- and 4-day mellowing periods, followed by curing for 3, 7, and 14 days. Performance was evaluated through the free swell index (FSI), unconfined compressive strength (UCS), split tensile strength (STS), and a wet–dry cracking analysis, supported by microstructural and mineralogical tests. The results showed that MICP alone improved UCS by up to 156.5% and increased calcite content to 1.25%. SNF addition enhanced UCS by 200% and STS by 100% at 1% content. The combined approach significantly increased UCS up to 809.09% and reduced the FSI by 66.66%. The integration of MICP and SNF effectively improves soil strength, tensile resistance, and durability under cyclic conditions, offering a low-cost, eco-friendly solution. This approach supports Sustainable Development Goals 9, 11, 12, 13, and 15.