Assessment of the range of variation of N_γ from 60 estimation methods for footings on sand

The range of variation of the bearing capacity factor, N_γ, was assessed using 60 estimation methods for rough footings on sand subjected to static vertical loading. The influence on the N_γ values of the use of correlations for the estimation of the friction angle, φ, derived from in situ tests was also assessed. The analysis shows a marked dependency on the methods used to determine N_γ, showing differences for the same φ values of up to 267% between estimated values. Uncertainty in the estimation of φ, due to the use of correlations with in situ tests, leads to a range of variation for N_γ higher than that seen using the 60 estimation methods. Finally, given the regular use of the in situ standard penetration test (SPT) on sands, and based on a series of analyses using finite elements, a simplified method in terms of the SPT N-values is proposed for estimation of N_γ in footings on sands.