نوع مقاله : پژوهشی
نویسندگان
دانشکدهی مهندسی عمران، دانشگاه تربیت مدرس
چکیده
کلیدواژهها
عنوان مقاله [English]
نویسندگان [English]
In this paper, the influence of hydraulic parameters of soil-water characteristic curve hysteresis and water flow head and the mechanical parameters of net confining stress and specimen height are evaluated on the
unsaturated water coefficient of permeability of a clayey sand. For this, a series of unsaturated permeability tests are carried out on the understudying soil with a novel flexible wall permeameter for unsaturated soils designed and built in Tarbiat Modares University. The novel permeameter is capable to quantify air and water coefficients of permeability of unsaturated soils in various flow states at different isotropic confining stress. This apparatus is
composed of a flexible wall permeameter cell, pressure panel, and flow and volume change measuring systems. The cell of the apparatus is capable to distinctly control or measure the variation of pore air and pore water
pressures in top and bottom of samples in various consolidation stresses. Positive and negative pressures of the apparatus were set with the precision pressure regulators in pressure panel. The proper de-aired water for
permeability tests was also generated inside the pressure panel. Also, the apparatus enables automatic measurement of the inlet/outlet water volume of the soil sample with the accuracy of 0.01 cubic centimeters. The effect of hydraulic hysteresis and flow head on water coefficient of permeability is assessed through a set of tests on samples with the height of 1 cm for two flow heads of 40 and 80 kPa and in matrix suctions of 40 and 100 kPa on wetting curve and matrix suction of 100 kPa on drying curve. These tests were also repeated on samples with the height of 3 cm just in for the water flow head of 40 kPa to evaluate the effect of soil thickness on the water coefficient of permeability. The effect of net confining stress on permeability of understudying soil is also assessed through a set of tests on soil samples with the height of 1 cm and matrix suction of 100 kPa on wetting curve in flow head of 40 kPa and net confining stress of 100 and 200 kPa. The experimental results
indicate that for constant matrix suction, the water coefficient of permeability attained in drying cycle is more than similar values on wetting cycle. Additionally along each of drying or wetting curves, the water coefficient of permeability increases with reduction of matrix suction. Further, the hydraulic conductivity of understudying soil appeared to be independent of applied heads and Dacry law was valid for the range of water flow heads. The experimental results also corroborated that any change of the soil thickness has only increased the required time to reach a steady state for water flow, and the water permeability of soil samples was independent of the
sample thickness.
کلیدواژهها [English]
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