The Effect of valency on the compressibility of clays

Many studies have been conducted to investigate the physicochemical behaviour of pure clay minerals and predict their engineering performance in the field. However, there is no clayey soil consisting of only a single clay mineral. In this study, the physicochemical properties of a clayey soil taken from Çanakkale consists of different clay minerals, namely 40-50% montmorillonite, 20-30% illite and 10- 15%) kaolin was investigated. The CEC (Cation Exchange Capacity) of soil was determined 13 meq/ 100 g. The soil was washed with IN ammonium acetate solution to purify the soil from cations presented in the exchangeable cation sites. Then, IN chloride solutions of sodium, Na; calcium, Ca+2; and aluminum, Al+3 were used to make the soils homoionized. The tested engineering properties are Atterberg Limits, hydraulic conductivity, sediment volume and consolidation behaviour. The results reveal that the liquid limit of soil increases with increasing in the cation valence; the plastic limit of the soils is also consistent with the liquid limit. Furthermore, the shrinkage limit of soil supports the general behavior of index properties. The hydraulic conductivity of the soil also increases with an increase in the valence of the cation at any given void ratio. There is no considerable change in the compressibility of the soil when the cation valence increased. However, trivalent clay consolidate six times faster than monovalent and two times faster than divalent clay. These properties of tested soils are similar to those of kaolinite. The index properties of homoionized soil are also tested with different pore fluids such as n-hexane, ethanol and methanol. The volume basis liquid limit results of homoionized samples were compared while treating with different pore fluids. Decrease in the dielectric constant of the pore fluid results decrease in volume basisIV liquid limit of homoionized specimens while treating with methanol. Then, volume basis liquid limit of homoionized specimens tend to increase when they were treated with ethanol. However, the volume basis liquid limit of samples decreased with n- hexane. On account of rapid evaporation of n-hexane, a correction was applied to the volume basis liquid limit values. Sedimentation test results were taken into consideration while applying the correction to the volume basis liquid limit of homoionized samples when treated with n-hexane. The obtained results are compared with the published data in the literature. The comparison revealed that the physicochemical behavior of the tested clay soil is, in general, between those of kaolinite and montmorillonite. However, when the pore fluid is inorganic the tested physicochemical parameters are close to those of kaolinite and when the pore fluid is organic the tested physicochemical parameters are close to those of either montmorillonite or kaolinite.