The Effect of Saline Water on the Physical and Mechanical Properties of Cohesive Fine-grained Soils (Case Study, Madani and Malekian Dams in East Azarbaijan Province)

Fine-grained soils with a high percentage of clay minerals are used for covering sanitary landfill and for earth dams' cores because of their low permeability. One of the key factors affecting the behavior of these soils is pore fluid chemistry, so that changes in fluid viscosity and type of cations change the engineering properties of these soils. In this study, the effect of water salinity has been investigated on Atterberg and compaction characteristics, shear strength, pore water pressure of fine-grained soils. For this purpose, Atterberg limits, compaction and undrained triaxial tests were conducted on the fine-grained soils, used in the cores of Shahid Madani and Malekian dams, with different pore fluids. Distilled water, project salty water, NaCl solutions with 0.2, 0.4, and 0.8 molar are used as a pore fluid. The results showed by increasing the salinity of water, the liquid limit, plastic limit and plasticity index decrease in both soils, but these changes are not considerable. The results of the triaxial tests showed increasing NaCl salt concentration does not always increase the shear strength of the soils. The maximum increase in the soil shear strength values in both Malekian and Madani soils was obtained with 0.2 molar which is mentioned as an optimal point. In both soils, by increasing the salinity of water, the excess pore water pressure decreases and there is not any meaningful effect on the deformation modulus secant of soils. The cohesion parameter in both soils are reduced up to 0.4 molar and after that increased by increasing salinity. The saline water with concentration between 0.2 and 0.4 molarraised the internal friction angle of soil and beyond these concentration did not have a positive effect on the friction angle.