Attom, MousaAlmasaeid, Mohammad Suleiman2023-06-122023-06-122022-1135.232-2022.63http://hdl.handle.net/11073/25265A Master of Science thesis in Civil Engineering by Mohammad Suliman Almasaeid entitled, “Stabilization of Sandy Soil Against Internal Erosion Using Fly Ash Mixed with Alkali-Activated Binder”, submitted in November 2022. Thesis advisor is Dr. Mousa Attom. Soft copy is available (Thesis, Completion Certificate, Approval Signatures, and AUS Archives Consent Form).Failure due internal erosion is one of the most common crucial failures in hydraulic structures, especially in embankment dams. It is defined as the movement of soil particles due to seepage force. This movement results in defects and a reduction in soil strength causing failure of hydraulic structures. Stabilization of soil is the best approach to avoid such catastrophic failure and prevent a huge loss of lives and properties. Many materials such as cement, lime, and bitumen have been used to stabilize the soil. These materials help in increasing the cohesion, and angle of internal friction and improve other properties of the soil. The main objective of this research is to stabilize sandy soil against internal erosion using fly ash (FA) alone and fly ash mixed with alkali-activated binder. To achieve the objective of this research, well-graded sandy soil was selected and mixed with fly ash alone and fly ash mixed with sodium hydroxide at different percentages. Compaction curves were determined for each percentage, and then specimens from the mix were remolded at 98% relative compaction and optimum moisture content corresponding to the compaction curve value. Hole Erosion Test (HET) was employed to evaluate the rate of erosion of sandy soil mixed with fly ash and fly ash with sodium hydroxide at different curing times (2 days, 7 days, and 28 days). Parameters such as friction factor, coefficient of soil erosion, and critical shear stress were obtained and used to determine the erosion rate index (IHET). It was found that using FA-NaOH significantly reduced internal erosion and increased the erosion rate index and the critical shear of the soil. The addition of 10% fly ash mixed with activated-alkali binder at 7 days curing time stabilized the soil against erosion. At this percentage, the soil was categorized as: “very slow erosion”. However, mixing the sand with fly ash alone has a small or insignificant effect on the internal erosion of the soil, especially at higher percentages of fly ash. The optimum percentage of fly ash alone was found to be 5% at 28 days of curing time.en-USInternal erosionPipingSoil stabilizingSoil erosionThesis