Research / GeomechanicsPrediction of Instabilities in Porous Media
Compaction bands are narrow, roughly planar zones of localized porosity loss. In the laboratory, the bands form perpendicular to the maximum compressive stress and are inferred to do so in the field. Although this mode of localization has been recognized only recently in porous rocks, it is common in a variety of other porous materials, e.g., cellular solids and metal foams. Both laboratory and field studies of the bands in sandstone have shown that their permeability is reduced by several orders of magnitude and that they form barriers to fluid flow across them. Consequently, their presence in subsurface formations would affect applications involving fluid injection or withdrawal, including sequestration of CO2 to mitigate adverse effects on the climate. Because the zones are narrow, they will be difficult to detect from the surface and, as a result, it is important to understand the conditions for their formation and extension.
The onset of liquefaction instability can be predicted by constitutive modeling via calculation of a critical plastic modulus using bifurcation theory. The method has already been shown to accurately reproduce static liquefaction as observed in triaxial tests on loose sands. This research is currently being expanded to predict potentially unstable regions of slopes using finite element methods. Soon, the constitutive model will be enhanced to allow for the prediction of liquefaction caused by earthquake loading.