چكيده به لاتين
Skeletal calcareous soils refer to soils consisting of skeletal remains of marine organisms. Marine calcareous sediments are quite prevalent in coasts of tropical regions. Significant differences have been observed between marine calcareous and silicate soils in terms of mechanical behaviors, shear strength, liquefaction resistance, etc., mainly due to considerable intra-particle voids in calcareous sediments. Although calcareous deposits are prevalent along coastal plains throughout the world, there is no study investigated their behavior in unsaturated conditions. In these conditions, soil-water retention capacity is a fundamental parameter in relation to many geotechnical, environmental, and agricultural aspects; and this capacity and subsequently unsaturated shear strength of a soil is expected to be influenced by intra-particle pores unique to calcareous soils.
In the present study, porous structure of calcareous soil was studied using Scanning Electron Microscopy (SEM) and Mercury Intrusion Porosimetry (MIP) tests; the results clearly revealed this special microstructural characteristic. To study water retention and hydraulic hysteresis behavior of different gradations of skeletal calcareous soil (obtained from the Hormuz Island of Iran) compared to a reference silicate soil (obtained from the Netherlands), series of tests were conducted using pressure plate and controlled-suction oedometer apparatuses. Besides, to find and/or modify a prediction method for water retention curve of calcareous soil with acceptable accuracy, several existing pedotransfer functions were evaluated. Moreover, constant water content (CW) triaxial tests were performed on two similar grain size distributions of both calcareous and silicate specimens to evaluate unsaturated shear behavior of calcareous soil for the first time, and compare it with a reference silicate soil. Saturated triaxial tests were also conducted to obtain saturated shear strength parameters of both soils.
All the Unsaturated tests (including pressure plate, controlled-suction oedometer, and controlled-suction triaxial apparatuses) were conducted in the Laboratory of Soil Mechanics (LMS) at École Polytechnique Fédéale de Lausanne (EPFL). Saturated triaxial tests were in the Geotechnical Research Center of Iran University of Science and Technology (IUST).
Test results showed that in similar grain size distribution of these soils, Water Retention Curve of calcareous and silica soils are almost the same in low suctions, but calcareous soil retains more water at higher suctions due to its intra-particle voids. In addition, owing to these microstructural pores, ratio of Sr reduction on wetting path of a hysteresis loop was found to be more for calcareous soil than silicate soil. Calcareous soil also experienced higher suction changes during CW tests. Effective stress parameter () and capillary cohesion of calcareous soil were indirectly influenced by its microstructure, and were higher compared to silicate soil. It also was observed that like the silicate soil, for the calcareous soil, critical state line was unique and close to saturated state.
