Enhancing the Engineering Properties of Gypseous Soil Utilizing Fly Ash

Abstract

Collapsible soils are robust in their natural, dry state but exposure to water leads to decomposition. They also undergo large volumetric changes often associated with the detachment of the ground surface. The construction on such type of soils is challenging duet to their costly need for treatment. Gypseous soil is considered one of the important collapsible soils and is typically found in desert and semi-arid areas with widespread moisture deficits. This study investigates the effect of fly ash as an amendment on the compressibility and shear strength of gypseous soil. A 51.23% of gypsum content is found in the soil samples collected from the city of Tikrit in the Salah al-Din governorate of Iraq. Fly ash is added at percentages of 4, 8, 12, 16, and 20% of the soil's weight. Direct shear and collapse laboratory tests are executed on both natural and treated soil. The findings demonstrated that the treated soil exhibited a significant increase in both cohesion and the angle of internal friction, and a decreased value of the Collapse Potential (CP). The collapsibility can be limited to 55.29% with a 20% addition of fly ash. The cohesion and internal friction angle are improved by 53.48% and 81.47%, respectively. Finally, the ideal percentage of fly ash ranges between 12% and 16%, as the enhancing ratio for both the collapse and the soil's shear strength significantly decreases beyond this percentage.