Modification of a Constitutive Model for Gassy Clay

Gassy clays containing large, discrete gas bubbles are widely spread in deposits in shallow waters. The existence of gas bubbles may impair the original soil structure, resulting in the instability of offshore foundations and the occurrence of submarine landslides. Although gassy clay was found to exhibit different undrained shear behaviors with variations of the initial pore water pressures and initial gas volume fractions, more experimental studies and theoretical interpretations of the relationship between the effective confining pressure and undrained responses are required. A series of undrained triaxial compression tests is conducted to compare the responses of reconstituted gassy and saturated specimens at an effective confining pressure of 200, 400, or 600 kPa. An existing elastoplastic constitutive model based on the critical state is improved by updating its stress-dilatancy function and yield surface. The dilatancy equation proposed has the potential to quantify the effect of gas bubbles on the dilatancy of the soil matrix. The yield surfaces are reproduced reasonably well by optimizing the expressions of shape parameters under a variety of effective confining pressures. The model developed can describe the stress-dilatancy and stress-strain responses of both the gassy and saturated specimens.