عنوان مقاله [English]
In most parts of the planet including Iran, soil layers are above the groundwater level and in unsaturated state. Various activities associated with soils, such as subsurface explorations, foundation engineering and building constructions in unsaturated soils, etc., necessitates the study of the properties of unsaturated soils. Historically, the studies and activities associated with saturated soils precedence over the saturated soils owing to the strong theoretical basis and less cost for saturated soils. Consequently, the need for understanding the behavior and properties of the unsaturated soils is a great concern for engineers and professionals when dealing with this type of soils. Important issues for predicting geotechnical behavior of unsaturated soils are determination of the soil water characteristic curves (SWCCs) and unsaturated hydraulic conductivities. The SWCCs has been found to be a conceptual tool by which the behavior of unsaturated soils can be understood. The SWCCs defines the relationship between soil matric suction (the difference between the air and water pressure in the soil) and the water content. In this study, in order to accurately analyze the geotechnical behavior and recognize the effect of soil type on soil-water and hydraulic characteristics of unsaturated soils including sand, silt and clay, three types of soil with different particle sizes was studied from the Nazlo region of Urmia City. To achieve SWCCs, a pressure plate apparatus with pressure control panel was designed and built. Laboratory results were analyzed with Brooks-Corey and Van Genuchten models implemented in RETC computer code. The suction-hydraulic conductivity relationships of the soil samples were analyzed with the Brooks-Corey and Burdine model as well as the Van Genuchten and Mualem model. By analyzing the results of laboratory SWCCs up to 200 kPa matric suction, it was verified that as fine grained particles of the soil samples increased, the water holding capacity of the soils was also increased. Consequently, the air-entry value, residual water content and saturated water content were increased. It was concluded that factors such as soil type, plasticity index and soil texture affect water holding capacity of soils and therefore change the geotechnical and hydraulic behavior of unsaturated soil.