Expansive soils have a large variation in volume depending on the quantity of water in them. Expansive soil problems pose structural and geotechnical engineering challenges , the aim of this study that investigate the effect of fly ash powder on the high plasticity clay around the five different locations in Erbil city (L1-Rashkin, L2-Raod of Musol, L3-Italy City, L4-Bahrka, L5-Traffic Station). The Fly ash powder could be use as a stabilizing material for high-plasticity clay that has caused damage to different buildings and roads. Grain size analysis, specific gravity, and Atterberg limit were the main methods of physical testing of soil, direct shear test, compaction and consolidation test were the main methods of the engineering testing. In the first stage were determined the Grain size analysis, Specific gravity, Atterberg Limit, shearing strength, compaction and paprameters of consolidation such as compression index and swelling index, and void ratio. Stabilization of the swelling soil was performed by adding three different percentages of fly ash powder (5%, 10%, and 15%). The results show that liquid limit, plastic limit, plasticity index, void ratio, Compression index, and swelling index were decreased with increasing fly ash to swelling soil. While the cohesion and dry density were increased with increasing fly ash powder percentages because this powder is composed of calcite and Muscovite non-clay minerals depending on XRD analysis.
Further the minerals composition of studied soil samples in the five studied areas (L1, L2, L3, L4, and L5) composed of Palygoreskite, Kaolinite, Chlorite, Illite, Sepiolite, Serprntinite minerals, and Semectite group minerals especially Montmorilonite as the swelling minerals and non-clay minerals of each samples composed of Quartz, Calcite, and Muscovite, While Fly ash powder composed of Muscovite, and Calcite without Quartz.