An Analytical Study of Annular Raft on Granular Piles

Rafts are frequently used to design foundations on soft soils to minimize the overall and differential settlements of structures built on them. In many cases, the raft alone can offer sufficient bearing capacity and all that is needed to restrict foundation settlements to a predetermined level with a few widely spaced piles. Granular piles (GPs) can be used due to their several advantages over steel or concrete piles. An annular raft foundation is generally provided for overhead water tanks, chimneys, etc. The provision of granular piles underneath the annular raft foundation not only increases the capacity of the foundation but also minimizes the settlement to an acceptable level. The present study deals with a rigorous analysis of annular raft foundation supported by GPs based on the continuum approach. A new numerical method is developed with geometric considerations for excluding the loaded pile portion from the region of the raft area by considering two distinct zones. This article introduces a novel approach, the annular raft over granular piles, which represents an innovative solution in geotechnical engineering. This innovation has the potential to improve the efficiency and effectiveness of foundation design in various construction projects. The response of annular raft foundation with GPs is evaluated in terms of settlement influence factor (SIF), load shared by granular piles (in %), and normalized shear stress variation along the GP–soil interface. The present study reveals that the presence of the pile influences the stress distribution locally. The stiffness of GP, relative length of GP, relative size of the raft influence the settlement and load sharing of annular raft with GPs.