Enhanced tensile strength of soft clay with coir fiber and rice husk ash waste

Abstract Soft clay possesses high plasticity, low bearing capacity, and considerable compressibility, making it unsuitable for foundation subgrade applications without sufficient stabilization efforts. This study examines the tensile strength of soft clay soil chemically and mechanically stabilized by utilizing rice husk ash (RHA) and coir fiber as sustainable additives. RHA was introduced at varying concentrations of 0%, 2%, 4%, 6%, 8%, and 10%, while coir fibers were used at a fixed concentration of 0.75% with a 50 mm fiber length. Samples were cured for 14 and 28 days. Splitting tensile strength tests were performed according to the ASTM D3967 standard. The findings revealed that the highest tensile strength, reaching 104.03 kPa, was achieved by adding 0.75% coir fibers and 2% RHA after a 28-day curing period. This value represents a 13.57-fold increase compared to the unstabilized sample. Consequently, a 2% RHA content was determined to be the optimum composition, and extended curing durations significantly improved the soil’s tensile strength. The addition of RHA resulted in more symmetrical lateral deformation, indicating a more even load distribution and a more stable mixture. Thus, RHA and coir fibers have demonstrated potential as eco-friendly alternative materials for stabilizing soft clay.