## 1 Introduction  
The industrial revolution and the significant technological developments of the last century have allowed people to use more energy than previous generations. The electric energy in the United States is generated using a variety of resources. The three most common resources are coal, natural gas, and nuclear power. According to the American Coal Ash Association (ACAA), nearly 38 million tons of fly ash were generated in 2016 and about 22 million tons (57%) were reused in beneficial applications, including concrete production, flowable fill, embankments, agriculture, mining applications, road pavement, soil amendments, material recovery, and waste stabilization, while the rest of the production was sent to disposal basins [1]. Fly ash has a broad range of applications within the construction industry [2]. The application of fly ash as a partial replacement for Portland cement in concrete is widely used, with considerable volumes. Fly ash utilization to stabilize soil or to enhance the engineering properties of soil, which is the primary focus of this study, uses only 0.34% of the total fly ash produced in the USA, and 1% is used for waste stabilization. In road base and sub-base material, the utilization was 1%, with structural fills and embankments using over 5% [2]. Fly ash has been used as a soil stabilizer in the highway and transportation industry in different layers and different methods. Fly ash has also been used to increase the stability of road embarments by strengthening soft subgrade soil. However, utilizing higher percentages of fly ash in silty soil or clayey sand stabilization has not been widely explored and there is a lack of research on this topic. This uncommon issue is probably due to the chemical composition and mechanical properties of fly ash that are generally not the same for the fly ashes that are produced from the same coal source in the same plant in different time periods [3]. As a result, the behavior of a high percentage fly ash-soil mixture has not been fully investigated and understood. [PERSON] et al. [4] studied the stabilization of clayey soil with a several percentages of fly ash, with a maximum of 12.5%. Their study found that a soil mixture with 7.5% fly ash provided the highest California Bearing Ratio (CBR) and unconfined compression strength (UCS). [PERSON] et al. [5] studied the short- and long-term behavior of soil treated with fly ash contents of 5%, 10%, 15%, and 20%. The results of this study showed no significant difference between the Proctor results and a direct correlation of fly ash content and the maximum dry density (MDD). The soil mixture with 20% fly ash showed the highest maximum dry density for 80% of the soil samples tested. [PERSON] and [PERSON] [6] found that the MDD increased and optimum moisture content (OMC) decreased with increasing fly ash content for expansive and non-expansive clays that were treated with Class **F** fly ash content of 5% to 20% based on the dry weight of the soil. The results indicated that the addition of fly ash reduced the compressibility characteristics for both expansive and non-expansive clays and the effect of fly ash was more pronounced in the compressibility behavior of expansive clays. The stabilization of low-plasticity soil (CL according to Unified Soil Classification System (USCS), contains 34.1% sand and 65.9 fine aggregate, passes through sieve no. 200 with LL = 27%, PL = 19%, and PI = 8%) with Class C fly ash was studied by [PERSON] [7]. Different fly ash contents, such as 3%, 5%, 7%, and 10%, were mixed with the soil based on the dry weight of the soil. This study performed compaction tests according to Method A of ASTM D1557 and concluded that as the fly ash content in the mixture increases the MDD decreases, and the theoretical analysis of the decrease in the MDD indicated the fine particles and the light weight of Class **C** fly ash compared to the CL soil that was used in the study. The performance of fine sand treated with Class **F** fly ash was studied by [PERSON] et al. [2].