Stabilization of Expansive Soil by Using Fly Ash and Coir Fiber

Expansive soil presents considerable difficulties in building and geotechnical engineering due to its adverse volume alterations in response to moisture fluctuations. This research examines the application of coir fiber and fly ash as stabilizers for expanding soils. Coir fiber, a natural and biodegradable substance, and fly ash, a byproduct of coal combustion, were evaluated for their capacity to mitigate soil expansion. Comprehensive soil samples obtained from the Korean Export Processing Zone (KEPZ) underwent laboratory analysis. Per USCS classification, the soil is categorized as inorganic highly plastic clay (Liquid Limit= 51.14%, Plastic Limit= 26.07%, Plasticity Index= 25.07%) and as moderate to very expansive soil (Liquid Limit= 51.14%, Plastic Limit= 26.07%, Plasticity Index= 25.07%). The soil was amended with different proportions of coir fiber (0.25%, 0.5%, 0.75%, 1%) and fly ash (3%, 6%, 9%, 12%), followed by a series of standardized tests, including compaction and unconfined compressive strength assessments, to analyze the alterations in soil characteristics. The results indicated that incorporating coir fiber and fly ash substantially enhanced the engineering features of expansive soils. Coir fiber enhanced shear strength, reduced liquid limit, and augmented soil cohesion. Conversely, fly ash functioned as a pozzolanic substance, facilitating cementitious reactions and thereby enhancing soil stability. The combination of coir fiber and fly ash exhibited a synergistic effect on soil workability, plasticity, and strength.