Numerical analysis of liquefaction-induced bearing capacity degradation of shallow foundations on a two-layered soil profile

Earthquake-induced excess pore pressure build-up and the associated shear strength degradation of liquefiable soils may result in bearing capacity degradation and seismic settlement accumulation of shallow foundations, two detrimental effects which need to be taken into account in order to ensure a viable performance-based design. This paper focuses on the first effect, in the case of strip and rectangle footings, resting on a deep liquefiable soil layer overlaid by a thinner non-liquefiable clay crust. A simplified analytical methodology is presented, based on the Meyerhof and Hanna [14] composite failure mechanism and the use of a reduced friction angle for the liquefied sand. The methodology is verified and evaluated against parametric numerical analyses with the Finite Difference Method, applying an advanced bounding surface constitutive model to account for the liquefied sand response. In addition, the existence of a critical clay crust thickness is explored, beyond which subsoil liquefaction does not affect the bearing capacity of the foundation. (C) 2012 Elsevier Ltd. All rights reserved.