DETERMINATION OF ${bf N_gamma}$ BEARING CAPACITY FACTOR FOR RING FOOTINGS OVER GRANULAR SOILS WITH ECCENTRIC LOADS USING THREE-DIMENSIONAL NUMERICAL

Nowadays, ring footings are used widely in the civil engineering projects especially in structures with centric geometry. Among them, Telecommunication towers, water or oil tanks, bridge piers, and on shore structures are some examples. In addition to vertical or gravitational loadings, ring footings are implied by moments imposed by lateral loadings and hence, the ring footings are loaded by eccentric loads. In the literature review of bearing capacity of ring footings, there are many researches in which the vertical bearing capacity of such footings is studied and investigated in numerical, analytical and experimental categories. However, few researches exist for eccentric load of such footings. In the present paper, the Ngamma factor, which is one of the bearing capacity factors is determined by using numerical simulations for the ring footings rested on granular soils. Due to the essence of the problem, threedimensional analysis is applied using nite dierence method. Since a bearing capacity problem was only a function of plastic parameters of the soil including internal soil friction angle and cohesion, the so-called linear elastic- perfectly plastic Mohr-Coulomb model was used in the simulations. Associated ow rule was assumed in the simulations because the variation of soil dilatancy angle was aimed to be ignored and that a rule could be found among the results. These Interface elements were considered in the simulations because the partial uplift of the footing was aimed to be modeled under eccentric loads. At the start of modeling, the numerical modeling was veried by the virtue of numerical simulation of a centrifugal modeling experiment. The comparison of results expresses good agreements between the simulations and experiment. In the following steps, a number of numerical models was analyzed by changing soil friction angle as well as the load eccentricity. Finally, attempts were made to nd a mathematical expression for the determination of Ngamma factor dened as a function of the ratio of load eccentricity to the footing diameter, ring radii ratio and soil friction angle.