Three-dimensional elasto-plastic analysis for the undrained capacity of ring and circular footings embedded in heterogeneous clay

This paper addresses the evaluation of the bearing capacity of ring and circular footings that are embedded in non-homogeneous soils. A three-dimensional finite-difference analysis is employed using FLAC(3D) with soil modeled as a linear elastic-perfectly plastic material following Tresca criterion. The base of the footing is attached to the soil through rough interface elements, while smooth and rough interfaces were considered along the soil-footing sides. The numerical results are validated with those available in the literature. The analyses indicated that the undrained bearing capacity factors N-c depend on the ratio of inner to outer radius (R-i/R-0), as well as the roughness of the vertical sides. In addition, the swipe loading technique is employed in order to investigate the effect of inclined and eccentric loading on the failure envelope approach. From the analyses, the failure envelopes were observed to be influenced by R-i/R-0 ratio under vertical and horizontal loading. The non-dimensioned failure load in the vertical-moment V-M plane indicated that the geometry of the ring footing (R-i/R-0 ratio) reduces the ultimate vertical load capacity and increases the maximum moment capacity, compared to circular footings. Hence, a negligible effect was observed for different R-i/R-0 ratios in terms of normalized loads.