Lower-Bound Seismic Bearing Capacity of a Strip Footing Adjacent to an Existing Footing on Sand

Abstract

The ideal notion of footings placed in isolation is rarely implemented in practice and footings are often placed adjacent to each other, interfering with one another's performance. In this paper, the lower-bound finite-element limit analysis method is used to investigate the pseudostatic bearing capacity of a strip footing placed in close proximity to an already-existing strip footing, over cohesionless soil. The pseudostatic approach is used to model the seismic loading. Analyses conducted for different accelerations, soil friction angles, and service load magnitudes on the existing footing and spacings showed that while the presence of the existing footing can improve the pseudostatic bearing capacity of the new footing, an amplified rate of reduction with seismicity ultimately causes the new footing to withstand smaller accelerations compared with its isolated case. The increase in spacing generally reduced bearing capacity. An exception was observed for a friction angle of 40° for all service loads and pseudostatic accelerations, where a maximum in both bearing capacity and fluidization acceleration was observed around 0.1 of the footing widths.