A model to predict the undrained response of loose gassy sand

Submarine slopes in deltaic environments often consist of loose sand containing gas bubbles within voids. It has been speculated that the presence of gas bubbles is one of the causes of submarine slope instability problems. This thesis studies the effect of presence of gas bubbles on undrained behaviour of loose sand.; The presence of gas bubbles increases the compressibility of the pore fluid. Accordingly, gassy soil can be considered as saturated soil with compressible pore fluid. Gassy soils exhibit both volumetric strain and pore pressure changes during undrained shearing. This response has been found to be due to the partial (internal) drainage, a phenomenon that occurs due to the increased compressibility of the gas-water mixture.; An elasto-plastic stress-strain model for sand has been modified to account for the effect of increased compressibility that results in volumetric strain and pore pressure change during an undrained shearing of loose gassy sand. This has been achieved by coupling volumetric strain due to gas compression/expansion and dissolution/ex-solution with volumetric strain during the yielding of sand. The model simulation shows that presence of gas bubbles increases the undrained shear strength of soil, and this increase is retarded by excess pore pressure that is associated with gassy soil.