Effect of Soluble Salts on Mechanical Properties of Granular Subgrade for Road Pavements

The existence of soluble salts in granular materials of highway pavements has become a widely spread problem in Iraq. This research is performed to evaluate the influence of soluble salts on the engineering properties of a soil-aggregate material brought out from a road fill of a newly constructed rural road in Samawah city, south of Iraq. Soluble salts, represented by sodium chloride (NaCl), sodium sulphate (Na2SO4) and gypsum (CaSO4 center dot 2H(2)O), were added to the granular material by different percentages ranging from zero to 15% by weight of the dry soil. The influence of soluble salts on the maximum dry density, performed using the modified proctor compaction test, was obtained and plotted. The effect of soluble salts on the resilient modulus was investigated. Consolidated undrained triaxial results indicate that soluble salts may not adversely affect the main component of shear strength of the granular material. However, findings obtained using California Bearing Ratio (CBR) test show that the existence of soluble salts in the granular material can significantly reduce the CBR value, especially when the soaking period exceeds 15 days. The physical effect of soluble salts depends mainly on their solubility and rate of dissolution in addition to the amount of water that exists.