عنوان مقاله [English]
Ring foundations can be used for communication towers, water and oil tanks, and generally for most structures with axial ymmetry about the central axis perpendicular to the foundation. Since lower amount of construction material is used to build the ring footings compared to circular footings with the same external diameter, it can be considered a more efficient and economic foundation than circular foundations. The bearing capacity of shallow foundations depends not only on soil properties, but also on the shape of these footings. The classical relations developed for determination of bearing capacities of such footings are different for square, rectangular, circular and strip footings. A widely accepted relation for determining the bearing capacity of ring foundation cannot be found in literature. The bearing capacity of ring foundation has, therefore, been the subject of some studies in recent decades.
In this paper, the results of studies that have been conducted on physical and numerical models of circular and ring foundations are presented. The physical models were made from rigid material with small sizes. All the tests were performed in geosynthetic laboratory of Shiraz University. The computer code PLAXIS 3D foundation, which is finite element software, was used to perform the numerical analysis. Analytical analysis was also performed using classical methods. Finally, numerical, analytical, and laboratory results were compared. The results showed the significant effect of geogrid on the increase of bearing capacity of both types of foundations. In either case, considering circular and ring footings on unreinforced and reinforced sands with a geogrid layer, the results were close to experimental results. The results of numerical analysis of bearing capacity values were, however, lower than those obtained experimentally. The bearing capacities of ring footings were found to be higher than the capacity of counterpart circular footings in all similar conditions. The analytical results showed that lower values of bearing capacities compared to experimental and numerical results due to the scale effect.