Effect of ionic concentrations and ph on the Atterberg limit of cohesive soil

Abstract

The addition of salt to pore water can affect the behaviour of the soil by influencing the electrochemical forces exist between the solid, liquid and dissolved phases. Changes in geotechnical behaviour of fine grained soils under the influence of ionic concentrations and pH depends on the chemistry of the soil constituents and the pore fluid chemistry. The geotechnical modifications of soil behaviour largely depend on the clay particles and the diversities in the nature of the clay types is due to their specific surface and the net electrical charge on them. Generally, clay particles surface are negatively charged while its edges are positively charged. To preserve electrical neutrality the negative charge of the clay particle is balanced by the attraction of cations which are held between the layers, and on the surface of the particles. The charged clay surface together with the counter–ions in the pore water at the diffuse double layer. The present study focuses on the effect of the ionic concentrations of potassium chloride (KCl) and pH on the liquid limit of fine grained soil. Fall cone test was conducted to measure the liquid limit in different concentrations of the pore fluid, with each of the ionic concentrations prepared in four different pH values (3.5, 5.5, 7.5 and 9.5). From the test results, it was observed that the pH values generally has no significant effect on the liquid limit of the samples; while the liquid limit lightly undulated at lower pH values at ionic concentrations of 0.00001 M, 0.0004 M and 0.003 M, the pH values had least influence at higher ionic concentrations (0.1 M and 1.8 M) of KCL. This behaviour is attributed to the buffering effects of the relatively high solute content at 0.1 M and 1.8 M. On the other hand, the liquid limit decreased with increasing ionic concentrations of KCL. Increasing the ionic concentration reduces the thickness of the diffuse double layer thereby depleting the repulsive forces and hence increases the effective stress leading to flocculation of clay particles that gave rise to the reduction in the liquid limit of the clayey sample

Keywords: Liquid Limit, potassium chloride, pore fluid, ionic concentrations, pH