EVALUATION OF WATER RETENTION PROPERTIES OF HORMUZ ISLAND CALCAREOUS SOIL

The curve presenting the relationship between water content and the soil matric suction is called 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, they consist of skeletal remains of marine organisms. They are common in the tropics between 30circ North and South latitudes. Due to the nature of their origin, one of the most important attributes of the calcareous soils that makes 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 signifies 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 particular microstructural characteristic of the calcareous soil particles compared with those of silicate soils. Besides, a series of tests were conducted for determining the Soil Water Characteristic Curve for different gradations of calcareous soil (from Hormoz Island of Iran) and reference Silicate soils using pressure plate and controlled-suction oedometer apparatuses in Laboratory of Soil Mechanics (LMS) at Ecole Polytechnique Federale de Lausanne (EPFL). Studies on the soil textures have revealed a further level of porosity in calcareous soil due to its intra-particle pores and the 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 retained much more water than the silicate soil due to its intra-particle voids. The controlled-suction oedometer showed that owing to their microstructural pores, the hydraulic hysteresis behavior of the calcareous soils would be different from that of the silicate soil.