Using readily available natural fibers to reinforce the expansive subgrade soil through analytical and experimental studies

Expansive soils cause considerable challenges in road construction due to their volumetric changes, which can lead to pavement deterioration. Although conventional soil stabilizers are effective, they are too expensive and not environmentally friendly. This study examines the use of locally available teff and enset natural fibers, which are derived from the enset and teff plants, as sustainable alternatives for reinforcing expansive soil obtained from Wolaita, Ethiopia. The variations of the teff and enset fibers used in this study are 0.25; 0.5; 0.75 & 1%. The untreated soil displayed a Maximum Dry Density (MDD) of 1.429 gm/cm3, Optimum Moisture Content (OMC) of 25.71%, California Bearing Ratio (CBR) of 2.85%, and an Unconfined Compressive Strength (UCS) of 36.5 kilopascals. The incorporation of these fibers led to significant enhancements in these properties, with an increase of 4.4% in dry density, 163.2% in CBR, and 352% in compressive strength. Moreover, notable reductions in moisture content, plasticity index (PI), free swelling, and linear shrinkage were recorded, resulting in maximum decrease of 22.6%, 8.6%, 78.3%, and 81.2%, respectively. Optimal performance was achieved by adding 0.75% of each fiber type to the soil, cut to a length of 20 mm, which was compacted at its MDD and OMC. These findings suggest that such locally available natural fiber reinforcement can be a cost-effective and environment friendly solution for improving the engineering properties of expansive soils that can be judiciously utilized in road construction. Statistical models were developed to predict the CBR value based on other index properties of the soil showing close agreement with experimental findings.