عنوان مقاله [English]
The use of stone columns is one of the effective ways to increase the bearing capacity of soils. An alternative system that can provide sufficient lateral confinement to support stone columns and increase bearing capacity is geosynthetic encased stone columns. The purpose of this study is to compare the behavior of geotextile and geogrid layers in reinforcing stone columns in standard Ottawa sand. In this study, a series of triaxial experiments in the undrained state was used. In the case of the lowest confining pressure, the load bearing capacity for the geotextile reinforced column will be 1.18 times higher. Whereas for the geogrid-reinforced stone column, the load bearing capacity is 1.31 times higher. In this study, standard Ottawa sand, gravel with a unit weight of 17 kN/m3 and a friction angle of 47.8°, geotextile and geogrid layers, and triaxial test apparatus are used. Triaxial specimens were 10 cm in diameter and 20 cm in height. Stone column dimensions of 2 cm in diameter and 20 cm in height are selected, respectively. Due to the limitations in the laboratory and the simulation of natural conditions, the unit weight of sand samples and stone columns made in triaxial test molds were selected as 15 and 17 kN/m3, respectively. Precipitation is used to fabricate sand cylindrical samples for triaxial testing. In this method, firstly attach the membrane to the underside of the triaxial apparatus and fasten the detachable bifurcation mold to the membrane and attach the membrane to the detachable mold walls by suction pumping about 2 bars. The important point is that, to achieve the same porosity, this distance must be kept constant throughout the precipitation process. Triaxial CU experiments on sand soil (SW) carried out in three cases: unreinforced, reinforced using geotextile encased stone column, and reinforced using geogrid encased stone column. In triaxial experiments, three confining pressures of 200, 300 and 400 kPa were used. The results indicate that the presence of geosynthetic encasements are very effective factor in increasing the bearing capacity. However, the main point of this study is that in conditions where the confining pressure is lower, these layers will have a better performance in comparison with the unreinforced conditions, in increasing the bearing capacity of sandy soils. This means that in the case of low confinement stress, the role of the encasement is more significant than in the case of high confinement stress.