Effect of Coir Fiber (As Natural Fibers and as Geotextile Sheets ) on Engineering Properties of Subgrade Soil (Clayey Soil )

Subgrade soil plays an important role in the performance of pavement structures. Clayey soils generally possess low bearing capacity, high compressibility, and poor drainage characteristics, which can lead to pavement failure. Soil stabilization techniques are therefore required to enhance the engineering properties of such soils. In recent years, natural fibers have been widely used as sustainable reinforcement materials in geotechnical engineering. Among these fibers, coir fiber derived from coconut husk is considered a promisingmaterial due to its high tensile strength, biodegradability, and availability.The present study investigates the effect of coir fiber used in two forms: randomly distributed natural fibers and coir geotextile sheets, on the engineering properties of clayey subgrade soil. Laboratory tests such as Standard ProctorCompaction Test, Unconfined Compressive Strength (UCS) Test, and California Bearing Ratio (CBR) Test were conducted on untreated soil as well as reinforced soil samples. Different percentages of coir fiber were mixed with soil, and coir geotextile sheets were placed at different depths within the soil specimens. The experimental results show that the inclusion of coir fibers significantly improves the strength characteristics of clayey soil. The use of coir geotextile sheets further enhances the load bearing capacity of soil. The study demonstrates that coir fiber reinforcement can be an economical and environmentally friendly method for improving weak subgrade soils used in pavement construction Keywords—Clayey soil, coir fiber, soil stabilization, CBR, UCS,pavement subgrade.