An updated simplified pore water pressure model for loosely coupled effective stress analyses

The use of nonlinear dynamic analyses in effective stress conditions has been recognized as an essential tool for demonstrating the system response of soil columns, i.e., the interaction among soil layers and the dissipation/redistribution of the seismically induced excess pore water pressure during and after the shaking. These analyses contributed to a better understanding of the mechanisms beyond the occurrence or not of liquefaction manifestations at the surface, by overcoming the limitations of the existing methods based on empirical charts. In the framework of the effective-stress nonlinear dynamic analysis, two distinct approaches can be adopted to predict earthquake-induced pore pressures: a ‘loosely coupled’ approach in which pore water pressure generation is calculated using semi-empirical models and the effects of generation and cyclic degradation are included by degradation of soil strength and stiffness; a ‘fully coupled’ approach in which the formulation of the constitutive law is developed in the effective-stress space. In this paper, a simplified stress-based pore water pressure model, already implemented in a non-linear computer code according to a ‘loosely coupled’ approach, has been updated by improving the pore water pressure generation and considering the dependency from the applied seismic load. Application to two different types of soils as investigated in cyclic laboratory tests are performed with the scope to assess the efficiency of the updated model and also limitations and future perspective discussed under the light of possible applications in loosely coupled effective stress analysis.