ABSTRACT
Three issues related to the mechanics of pore water pressure generation and liquefaction of soils is presented. First, drained compression experiments were conducted on sand at very low effective confining stresses in the range of 0.05 – 2.00 kPa both in a microgravity environment and on Earth for densities ranging from 10% to 85%. It was observed that the peak friction angles were as high as 75.0° at 0.05 kPa confining pressure and D r = 65%, and 52.0° at 2.00 kPa confining pressure with D r also equal to 65%, while the dilatancy angles were in the range of 30°. It was observed that even very loose sands tend to dilate rather than contract in volume at these low effective confining stresses. Second, drained Directional Shear Cell experiments involving rotations of principal stress directions with respect to the material axes, and while the magnitude of the stress changed or remained constant, resulted in substantially different volume change patterns, which will results in similar pore water pressure behavior in an undrained situation. Third, theoretical and numerical analysis results show that localization of deformations in undrained soils and soil stability are highly dependent on the compressibility of the pore fluid relative to the soil skeleton, and that critical bifurcation directions in plane strain are always at 45°, while they remain highly variable for other stress states. The difference between the friction and dilatancy angles has substantial influence on behavior.
