MODELLING PORE PRESSURE BUILD-UP IN GASSY SOILS USING FLAC3D

The presence of a small gas phase in seemingly saturated soils has been regularly attested near the water table or in sediments containing organic matter. Meanwhile, research on the relationship between the degree of soil saturation and liquefaction resistance has shown that even a small quantity of gas can significantly reduce pore pressure buildup. For this reason, accounting for the presence of this gas phase could help optimise the seismic design of geotechnical structures. The aim of this paper is to propose a methodology for modelling seismic loading of gassy soils using the commercial software FLAC3D. To achieve this, we propose a fluid compressibility model allowing us to homogenise water and gas phases into a single equivalent pore fluid. Using an in-built functionality of FLAC3D, this model is inserted into the software, allowing it to continuously update both saturation ratio and fluid bulk modulus during loading. Coupled with the P2PSAND constitutive model, this approach is tested on a series of cyclic triaxial tests performed on Hostun sand.