Experimental and numerical investigation of the influence of relative density on the behavior of ring footings on an inclined surface

Ring footings are a crucial foundation type for supporting large and tall structures, as they enhance structural stability, mitigate the risk of overturning, and resist lateral forces. Compared with conventional circular foundations, ring footings also provide savings in construction materials and overall cost. This study examines the behavior of ring footings with radius ratios of n = 0.25, 0.5, and 0.75. The models consist of steel footings with a thickness of 50 mm and an area of 2200 mm², placed on granular sandy soil with a dried unit weight of 16 kN/m³ and a relative density of 50%. The footings were positioned at a distance of b/Do​=1 from the slope crest to assess the influence of inclined surfaces. Centrifuge modeling was employed to simulate realistic field stresses, while numerical analyses were performed using PLAXIS 3D to verify and supplement the experimental data. The results show that the bearing capacity of ring foundations decreases as the surface inclination increases from 10° to 20°. On average, this reduction is about 10–15%, indicating the significant effect of slope angle on foundation performance. Furthermore, increasing the radius ratio of the footing leads to an additional decrease in bearing capacity, which aligns with previous studies. The combined experimental and numerical approach highlights the importance of considering slope inclination and geometry in the design of ring footings. These findings offer practical guidance for enhancing foundation stability and cost efficiency in geotechnical engineering applications involving sloping sandy soils.