Abstract
Fine grained sediments with undissolved gas bubbles are widely distributed in the seabed around the world. The gas bubbles are much larger than the clay particles and fit in the saturated clay matrix rather than the pore water. Generally, these bubbles tend to degrade the soil stiffness and strength. But when the difference between the gas and pore water pressure is sufficiently small, pore water in the saturated clay matrix can drain into the cavities, making the void ratio of the saturated matrix smaller, which makes the undrained shear strength of the gassy clay sample higher than that of a saturated one. Such soil response cannot be described based on the assumption that gassy clay is a soil with compressible pore fluid. A new constitutive model for describing the stress-strain relation for gassy clay is proposed. An important feature of the model is that the gassy clay is considered as a composite material with compressible cavities which could be flooded by pore water. Effect of gas cavities on plastic hardening on the saturated matrix is accounted for. The model has been used to predict the response of three gassy clays and good agreement between the test data and model simulations is observed. Potential improvement of the model is discussed.
Highlights
Gas-charged marine sediments are widely distributed in the seabed throughout the world
A new approach for modelling the mechanical response of gassy clay will be presented in this paper, in which gassy clay is considered as a composite material with compressible cavities which can be flooded by pore water
Gassy clay must be considered as a composite material with compressible cavities, which could be flooded by pore water
Summary
Gas-charged marine sediments are widely distributed in the seabed throughout the world. The model proposed by Grozic et al is based on the assumption that gassy clay is a soil with compressible fluid, which is not physically reasonable [6] It can only capture the beneficial effect of gas bubbles on the undrained shear strength of gassy clay, because compressible fluid makes the positive excess pore pressure smaller in an undrained test. Thomas has proposed a technique for modelling consolidation of gassy clay, in which gas bubbles are considered as compressible solids [8] This method gives good prediction for consolidation of gassy clay in oedometer tests but cannot describe the response of gassy clay in shear (like triaxial compression), in which the gas cavities can be flooded. A new approach for modelling the mechanical response of gassy clay will be presented in this paper, in which gassy clay is considered as a composite material with compressible cavities which can be flooded by pore water.
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