Journal of Earth Sciences and Geotechnical Engineering

Determination of the Shear Strength, Permeability and Soil Water Characteristic Curve of Unsaturated Soils from Iraq

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• Abstract

  The soil water characteristic curve (SWCC) defines the relationship between the amount of water in the soil and soil suction. The SWCC has been used as a tool either directly or indirectly in the prediction of the shear strength parameter and coefficient of permeability. In this paper, three undisturbed soil samples were collected from three sites within Baghdad city, Al-Rasafa region. The physical properties of these soils were studied by conducting a series of tests in the laboratory. For each sample, the SWCC is measured by the filter paper method. Fitting methods are applied through the program (Soil Vision), after indentifying the basic properties of the soil such as Attereberg limits, particle size distribution, specific gravity, void ratio, porosity and wet and dry unit weights. Then, the soil water characteristic curve is converted to relation correlating the void ratio and matric suction. The slope of the latter relation can be used to define the H–modulus function which is used for finite element analysis of unsaturated soil. Estimation the coefficient of permeability of unsaturated soil was also made and the undrained shear strength was measured for each value of matric suction. It was concluded that the matric suction value increases with decrease of the degree of saturation, and the undrained shear strength increases with increase of matric suction. Also, the coefficient of permeability decreases with increase of matric suction.