Ultimate Bearing Capacity of a Footing Considering the Interference of an Existing Footing on Sand

The ultimate bearing capacity of a new strip footing placed on a cohesionless soil medium, in the presence of an existing strip footing, the load on which is assumed to be known, has been determined. Both the footings are assumed to be perfectly rigid and rough. The analysis is carried out by using an upper bound finite element limit analysis. For different clear spacing (S) between the footings, the values of the efficiency factor (ξγ) were determined; where ξγ is defined as the ratio of the failure load for an interfering new footing of a given width (B) to that for a single isolated footing having the same width. For ϕ < 30°, it is generally noted that the magnitude of ξγ increases continuously with a decrease in S/B. For ϕ > 30°, on the other hand if the applied load on the existing footing is approximately greater than half the failure load for a single isolated footing having the same width, the peak magnitude of ξγ was found to occur at around S/B ≈ 0.1 rather than at S/B = 0. The increase in ξγ becomes further significant with an increase in the magnitude of the load on the existing footing.