مطالعه‌ي تاثير پارامترهاي هيدروليكي و مكانيكي بر روي ضريب نفوذپذيري آب در يك خاك ماسه‌يي رسدار با استفاده از دستگاه جديد تعيين نفوذپذيري در خاكهاي غيراشباع

EVALUATION OF THE EFFECTS OF HYDRAULIC AND MECHANICAL PARAMETERS ON THE WATER COEFFICIENT OF PERMEABILITY OF CLAYEY SAND WITH A NOVEL PERMEAMETER FOR UNSATURATED SOILS

اين نوشتار تاثير عوامل هيدروليكي رفتار وابسته به تاريخچه‌ي منحني مشخصه, هد جريان, عوامل مكانيكي تنشهاي همه‌جانبه, و ارتفاع نمونه بر روي ضريب نفوذپذيري آب در يك خاك ماسه‌يي رس‌دار بررسي شده است. لذا آزمايش‌هاي مختلف تعيين نفوذپذيري با دستگاهي جديد در مقادير مختلف مكش بافتي بر روي منحني هاي ترشدگي و ‌خشك‌شدگي در تنش هاي تحكيمي مختلف بر روي نمونه هاي خاك مفروض با ارتفاع 1 يا 3 سانتي‌متر انجام شده است. نتايج به‌دست‌آمده حاكي از بيشتربودن ضريب نفوذپذيري آب در مسيرهاي خشك‌شدگي نسبت به مسيرهاي ترشدگي بوده و كاهش مكش بافتي نيز باعث افزايش ضريب نفوذپذيري شده است. همچنين تغييرات هد جريان و ارتفاع نمونه‌ تاثيري بر روي ضريب نفوذپذيري خاك نداشته و افزايش تنش هاي همه‌جانبه در يك مكش بافتي ثابت نيز باعث افزايش درجه‌ي اشباع و ضريب نفوذپذيري شده است.

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 clayey sand. For this, a series of unsaturated permeability tests are carried out on the soil under study with a novel flexible wall permeameter for unsaturated soils, designed and built in Tarbiat Modares University. The novel permeameter is able to quantify air and water coefficients of the permeability of unsaturated soils in various flow states at different isotropic confining stresses. This apparatus is composed of a flexible wall permeameter cell, a pressure panel, and flow and volume change measuring systems. The cell of the apparatus is capable of distinctly controlling or measuring variations in pore air and pore water pressure at the top and bottom of the samples under various consolidation stresses. Positive and negative pressures of the apparatus were set with precision pressure regulators in the 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 an accuracy of 0.01 cubic centimeters. The effect of hydraulic hysteresis and flow head on the water coefficient of permeability is assessed through a set of tests on samples with a height of 1 cm for two flow heads of 40 and 80 kPa, in matrix suctions of 40 and 100 kPa on wetting curves and a matrix suction of 100 kPa on the drying curve. These tests were also repeated on samples with a height of 3 cm for a 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 the permeability of the soil under stud is also assessed through a set of tests on soil samples with a height of 1 cm, and a matrix suction of 100 kPa on the wetting curve in a 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 the drying cycle is more than similar values in the wetting cycle. Additionally, along each of the drying or wetting curves, the water coefficient of permeability increases with a reduction in matrix suction. Further, the hydraulic conductivity of the soil under study appeared to be independent of applied heads, and the Dacry law was valid for the range of water flow heads. The experimental results also corroborated that any change in 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 sample thickness.