NUMERICAL ANALYSIS OF RING FOOTINGS RESTING ON SAND BEDS

Nowadays, more and more ring footings are used in practice specially for axi-symmetric structures. In this paper, a numerical analysis was performed using PLAXIS software for calculating bearing capacity factor for rough circular and ring footings on sand. The analysis was carried out using Mohr-Coulomb’s criterion for soil. The bearing capacity was calculated for rough circular and ring footings and then the bearing capacity factor was calculated. The effect of different factors such as angle of internal friction of sand, , radius ratio () and different external diameters of circular and ring footings () were studied. The load settlement curves for circular and ring footings were compared, with emphasis on the ultimate bearing capacity. The analysis indicated that radius ratio has a significant effect on the ultimate bearing capacity of ring footings, were ultimate bearing capacity decreases with increasing radius ratio. However, little or no change in bearing capacity factor was observed. Also, the results indicated that there is no significant effect of footing size () on the bearing capacity factor value. It is found that the space in ring footing () has a significant effect on the change of failure mode of soil from both local and punching shear failure to a general shear failure for loose and medium sand, respectively. Also, the space in ring footing has a significant effect on the length and width of failure zone under ring footings. Nowadays, more and more ring footings are used in practice specially for axi-symmetric structures. In this paper, a numerical analysis was performed using PLAXIS software for calculating bearing capacity factor for rough circular and ring footings on sand. The analysis was carried out using Mohr-Coulomb’s criterion for soil. The bearing capacity was calculated for rough circular and ring footings and then the bearing capacity factor was calculated. The effect of different factors such as angle of internal friction of sand, , radius ratio ( ) and different external diameters of circular and ring footings ( ) were studied. The load settlement curves for circular and ring footings were compared, with emphasis on the ultimate bearing capacity. The analysis indicated that radius ratio has a significant effect on the ultimate bearing capacity of ring footings, were ultimate bearing capacity decreases with increasing radius ratio. However, little or no change in bearing capacity factor was observed. Also, the results indicated that there is no significant effect of footing size ( ) on the bearing capacity factor value. It is found that the space in ring footing ( ) has a significant effect on the change of failure mode of soil from both local and punching shear failure to a general shear failure for loose and medium sand, respectively. Also, the space in ring footing has a significant effect on the length and width of failure zone under ring footings.