This paper presents shear strength test results and structural changes in clay soils with acetic acid. Two different clay soils were used, kaolinite and another containing montmorillonite with a mixed mineralogy, while pure water and various contents of acetic acid (20%, 40%, 60% and 80%) were used as pore fluids. Clay-pore fluid slurries prepared with a water content of twice the liquid limit of each acetic acid content were consolidated under a 100 kPa pre-consolidation pressure. Direct shear tests were conducted on samples taken from pre-consolidated mixtures in order to determine changes in shear strength. Additionally, optical microscope images and scanning electron photomicrographs were obtained in order to observe structural changes under the influence of acetic acid.
According to the experimental results, significant increases occurred in peak shear strength and shear strength parameter values in both clays in parallel with increasing acetic acid content. These increases were higher in the clay with montmorillonite; in particular, there were substantial changes in the internal friction angle. Increasing liquid limit values with increasing acetic acid contents in kaolinite resulted in a substantial decrease in the other clay. The optical microscope images and scanning electron photomicrographs indicated that lumpy formations occurred in both clays with the addition of acetic acid, and their structures began to resemble that of a silt and fine sand form