عنوان مقاله [English]
The curve presenting the relationship between water content and the soil matric suction is called the soil water characteristic curve, SWCC. The water retention potential of the soils is dependent on grain size distributions (GSD), soil texture, and soils origins. Calcareous soils are soils with a high carbonate content, unique particle shapes, and high intraparticle porosity; and, are consist of skeletal remains of marine organisms. They are common in the tropics between 30° North and South latitudes. Due to the nature of their origin, one of the most important attributes of the calcareous soils that make their properties different from those of silicate soils is their significant intra-particle void space. The majority of near-surface soils are unsaturated over at least some portion of the year; consequently, the calcareous intra-particle porosity coupled with soil suction as the main characteristic of unsaturated soils, signify the necessity of the studies of calcareous soil behavior under unsaturated conditions. In this study the Scanning Electron Microscopy (SEM) and Mercury Intrusion Prosimetry (MIP) tests were performed to study the especial microstructural characteristic of the calcareous soil particles in compare with those of silicate soils. Besides, series of tests were conducted for determining the Soil Water Characteristic Curve for different gradations of calcareous soil (from Hormoz Island of Iran) and a reference Silicate soils using pressure plate and controlled-suction oedometer apparatuses in Laboratory of Soil Mechanics (LMS) at École Polytechnique Fédérale de Lausanne (EPFL). The studies on the soil textures revealed a further level of porosity in calcareous soil due to its intra-particle pores and the its samples with larger grain sizes showed higher intra-particle porosity. The pressure plate test results showed that for similar gradations of silicate and calcareous soil, in higher suctions, the calcareous soil retains more water than the silicate soil due to of its intra-particle voids. The controlled-suction oedometer showed that owing to their microstructural pores, the hydraulic hysteresis behavior of the calcareous soils is different from that of the silicate soil.