Experimental Investigation on Sustainable Soil Stabilization Using Coconut Coir Fibre

As urbanization grows, engineers increasingly turn to fiber-reinforced soil, utilizing natural and synthetic fibers to enhance its strength, stability, and sustainability. However, limited experimental studies have systematically evaluated the influence of coconut coir fibre content on the mechanical behaviour of soils. Therefore, this study investigates the potential of waste coconut coir fibres as a reinforcement material to improve the engineering properties of soil, including shear strength, compressibility, and bearing capacity. The investigation compares the results of Direct Shear Test (DST) and Unconfined Compressive Strength (UCS) tests conducted on two distinct soil samples. For Soil Sample-1, the DST showed a 67.5% increase in cohesion (from 19.6 kPa to 32.8 kPa) and a 70.4% increase in the angle of internal friction (from 19.9° to 33.9°), indicating a significant improvement in shear strength. The UCS test showed an 18.5% increase in peak stress (from 0.054 to 0.064 MPa) at an optimum fibre content of 0.35%. For Soil Sample-2, the DST revealed a 47.5% increase in cohesion (from 28.9 kPa to 42.7 kPa) and a 63.2% increase in the angle of internal friction (from 22.0° to 35.9°), while the UCS results showed a 50% improvement in peak stress (from 0.070 to 0.105 MPa). The findings suggest that coconut coir fibre reinforcement significantly enhances the shear strength and compressive strength of soils, with Soil Sample-2 exhibiting a more pronounced improvement. The results indicate that an optimum fibre content of 0.35% provides the maximum improvement in soil strength characteristics, demonstrating the feasibility of coconut coir fibre as a sustainable soil stabilization material. Overall, the study highlights the potential of waste coconut coir fibre as a technically viable and environmentally sustainable alternative for soil stabilization applications. Future research may focus on optimizing fibre treatments for different soil types and evaluating long-term performance under field conditions.