The permeability of unsaturated silt-sand soil is important in many geotechnical and geoenvironmental challenges. Therefore, an appropriate method to evaluate silt-sand soil permeability is important, particularly in Iran where it received little consideration. In this in vitro research, different amounts of fine silt were evaluated on behavior of an unsaturated silt-sand soil with different grain size distribution using a new modified triaxial apparatus. Permeability was measured against matric suction and volumetric water content, and the results are compared against experimental models. The results indicated that the behavior of unsaturated sandy soil permeability could be determined as a function of matric suction, soil void size, and percentage of fine aggregate. Furthermore, the results appeared to imply that an increase of fine contents reduced the permeability, specifically at higher values of suction. This trend for the reduction of soil permeability was related to the increase in the amount of fine contents.

This article presents the results of a laboratory test programme on two different soils, conducted to examine the influence of the initial dry density on the soil-water characteristic curve elements along drying and wetting paths. Particular attention was paid to determine the contributions of the initial compaction effort to the rates of saturation and desaturation, size of hydraulic hysteresis, air entry and air expulsion values. Drying and wetting tests were performed on samples compacted to different dry densities with identical water contents. The general patterns observed are discussed and compared in relation to some available data from the literature in order to determine the applicability of the detected trends to other soils. Additionally, it is shown that the horizontal separation of the air entry and air expulsion values could be a suitable method for estimating the size of hydraulic hysteresis.

This article presents the results of a careful laboratory programme aimed to examine the influence of initial dry density, moisture content, degree of saturation, and matrix suction on the California bearing ratio (CBR) of a pavement material along drying and wetting paths. To this end, the CBR value of a sand-kaolin mixture was measured in a range of initial void ratios and initial water contents along drying and wetting portions of the soil-water characteristic curve (SWCC). Wetting CBR tests were performed on the soil samples that were compacted and wetted to different dry densities and water contents. For drying tests, soil samples were prepared identically to the soil samples used in wetting tests, but after the compaction, they were desaturated by using the air-drying technique. The general trends observed are discussed and are compared in relation to some available data in the literature. Additionally, the experimental data appeared to show a distinction in the response of CBR along drying and wetting paths. The hysteretic detected response of CBR was discussed with relation to the hysteretic nature of the SWCC.

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