Exploring the effect of adding nano-silica and cement on the unconfined compressive strength of soft clay

Clay soils with a water content of more than 35% or close to the liquid limit are known as soft clay. These soils have an unconfined compressive strength (UCS) of less than 25 kilopascals. In order to improve the strength of these soils, additives such as cement and nanoparticles are added to them. These additives are combined with soil, which is called cemented mixed soil. Therefore, this research investigated the effect of the simultaneous addition of Nano-silica with cement on changes in UCS of soft clays with low plasticity (cl). The research considers soil with a constant water content of 40%, exceeding its liquid limit, for all samples. The changes in three factors, the cement and Nano-silica content consumed and the curing time of the specimens, were investigated as effective factors. For cement, 8%, 10%, and 12% relative to the weight of dry soil were considered. Nano-silica at eight levels from zero to 1.4% relative to the weight of dry soil and three curing times 7, 14, and 28 days were considered. A total of 72 series of specimens were made, and the unconfined compressive strength was measured. The results indicate that using nano-silica up to 1.2% in combination with cement increases the UCS by an average of about 170% after seven days, 120% after 14 days, and 48% after 28 days compared to using cement alone. Additionally, adding nano-silica led to a reduction of up to 4% in cement usage. Equations were derived based on the consumption rates of cement and nano-silica, along with the curing period, to estimate the uniaxial strength of the samples. The average difference between the estimated and measured values for all samples ranged from 1% to 3%.