Experimental Investigation of the Behavior of Ring and Circular Footings on Geogrid Reinforced Layered Soil Strata

Extensive research has been conducted on the performance of footings on both uniform and layered soil strata, focusing on conventional footing designs. Ring footings, on the other hand, have not undergone thorough field and laboratory evaluations, particularly for multi layered soil strata. A series of laboratory tests were performed with ring and circular footings resting on different homogeneous and layered soil strata. The study considered multiple unreinforced and reinforced foundation configurations by altering the thicknesses (H) of the top layer, in the range of 0.66–2.66D, overlying the subgrades of varying relative density, ranging from very loose (Dr_B = 30%) to stiff (Dr_B = 50%, 80%). The findings of the study suggest that the performance of foundations is significantly affected by the placement of geogrid at the interface between the layers. A profound improvement in the performance with respect to the load bearing capacity and reduction in footing settlements was observed due to the introduction of geogrid. However, the extent of improvements was influenced by the relative density of the subgrade, the level of settlement experienced by the footing, and the thickness of the top layer. The effectiveness of reinforcement was reduced as the lower layer stiffness and the top layer thickness increased. The study observed the highest improvement of 2.3 in terms of bearing pressure ratio for H = 0.66D and Dr_B = 30%. In both the unreinforced and reinforced cases, it was observed that the ring foundation with the optimal diameter ratio exhibited higher bearing pressures than the circular foundation with the same outer diameter.