Bearing capacity of open caissons embedded in sand

Abstract

Open caissons are an increasingly common means of constructing underground storage and attenuation tanks as well as launch and reception shafts for tunnel-boring machines. The caisson walls typically feature a tapered base, referred to as the ‘cutting face’, to aid the sinking process by reducing the vertical soil reaction. The primary aim of this paper is to explore the influence of the caisson cutting face inclination angle on the vertical soil reaction in sand. Both finite-element limit analysis and finite-element analysis are adopted for this purpose. The effects of cutting face roughness, external embedment depth and caisson radius are also investigated. The results show that the influence of the cutting face inclination angle on the bearing capacity is highly dependent on both the soil friction angle and the roughness of the cutting face. A reduction in the caisson radius is also shown to cause a significant increase in the vertical soil reaction. The numerical output is used to inform the development of a new closed-form analytical approach amenable for use in routine design. The design method is shown to provide a high-fidelity representation of the numerical output.