Development of a simplified method for the estimation of seismic-induced pore water pressures under undrained conditions

The reduction of effective stress caused by the seismic-induced pore water pressure build-up occurring in saturated soils can be a remarkable issue. To avoid catastrophic consequences, the development of a reliable but still simplified method is needed to fairly estimate the liquefaction hazard of the site at hand. This work presents an update of the decoupled approach firstly proposed by Seed et al. (1975), where the term representing the rate of excess pore pressures under fully-undrained conditions is added to the well-known 1D consolidation equation. The assumption of a uniform distribution of the equivalent number of cycles over the earthquake duration has been hereby replaced by a more realistic assumption. This hypothesis has been then tested through a series of fully-coupled, nonlinear dynamic 2D Finite Element analyses.