Evaluation of Dissolved Gas Pressure in Sandy Soils

Abstract

Gassy sandy soils commonly occur in offshore regions, and slope failures during unloading are often inevitable in such soils as gas bubbles affect the compressibility of the pore fluid and integrity of the soil matrix. The ratio of pore water pressure to total dissolved gas pressure (PTDG) controls if and when free gas forms during unloading. PTDG has commonly been assumed equal to the pore water pressure, which may result in incorrect estimates during modeling and prediction of gassy soil induced failures. In this thesis, both total dissolved gas pressure and pore water pressure in gassy sandy soils were measured in a specially designed laboratory program that involved pressure reductions with undrained rebound conditions. It was concluded that PTDG and pore water pressure are not equal for sometime after the pressure reduction takes place. This difference in the two pressures accounts for the capillary pressure or surface tension effects.