Controllability criteria for soils saturated by a compressible fluid

The liquefaction of sediments with gas bubbles occluded in the pore fluid can be studied neither through classical methods for saturated soils nor through concepts valid for unsaturated soils with continuous fluid phases. To fill this gap, this paper proposes to adapt to gas-charged soils a set of techniques that until now has been used only for fully saturated soils or unsaturated media with a continuous gas phase. In particular, the pore fluid has been modeled as a homogenized liquid-gas mixture of nonnegligible compressibility, and an expression of second-order work for porous media filled by such a compressible fluid has been derived. The use of incremental constitutive relations for the solid-fluid mixture has thus enabled the definition of controllability criteria specific for quasi-saturated soils subjected to drained and/or undrained loading paths. Such criteria have been computed through an elastoplastic model for loose granular soils and have been used to reinterpret evidence from laboratory experiments on gassy sands. In agreement with the evidence, the analyses indicate that the energy input associated with the compression of the fluid phase plays a crucial role in identifying the onset of flow failure and in predicting the variability of the liquefaction resistance with the degree of gas saturation. These findings demonstrate the applicability of controllability theories to a class of soils that was not encompassed by previous studies based on similar techniques. Therefore, they may find potential application in the risk assessment of mass movements in gas-charged submarine deposits and in the mitigation of near-surface geohazards.