The effect of acidic and basic tuff additives on consolidation of high plasticity clays

Stabilization is the most preferred method for improving basic engineering properties such as compaction, permeability and strength of clayey soils. As a result of the pozzolanic reactions that occur after stabilization in clayey soils by adding different types and ratios of additives, an increase in the strength of the soil and a decrease in the settlement, swelling and permeability occur. Lime, silica fume, fly ash, pumice, marble dust, cement and tuff are called as pozzolans and are the most commonly preferred natural or artificial materials used in stabilization. It is important that the pozzolans to be used should be economical, easily acquirable and environmentally friendly. Therefore, it is necessary to expand the use of natural materials such as pumice and tuff instead of artificial pozzolanic material and to examine the effects of such natural pozzolans on the engineering properties of clayey soils. In this study, acidic characteristic tuffs of Kizilkaya Formation that cropped out in Gumushane region and basic characterized tuffs of Karabakir Formation cropped out in Elazig region were selected as additive material. These tuffs were added to the high plasticity bentonite in different ratios and the effects of these tuffs over the consolidation properties and swelling potential of bentonite were investigated. Consolidation tests were carried out both before and after curing on the pure bentonite and tuff added samples those prepared for this purpose, and the effects of acidic and basic tuff additives on the consolidation coefficient (Cv), which gives information about the consolidation time in clayey soils, were determined. In addition, in order to determine the effects on the swelling potential, swelling pressure and swelling percentage tests were carried out both before and after curing on the additive-free bentonite and tuff added samples. As a result of the experimental studies, if the additive ratio was 5%, it was determined that acidic tuffs increased the Cv values of the samples more and decreased the swelling pressure when compared to basic tuffs. The effect of acidic and alkaline tuffs on the percentage of swelling is similar and the percentage of swelling in the samples decreases depending on the additive ratio. The results showed that both acidic and alkaline tuffs have a significant effect on the consolidation and swelling potential of high plasticity clayey soils.