Constitutive modeling for undrained shear behavior of gassy sand considering energy dissipation at the mesoscopic level

The gas phase in the gassy sand is in the form of occluded bubbles which are surrounded by water within the void space. Due to the high compressibility of the gas bubbles, it has a significant impact on the shear strength, volume change and other engineering properties of gassy sand. Based on the thermodynamic theory of granular matter, combined with the dilatancy equation considering the state parameter and the relationship between pore gas pressure and pore gas volume change, a thermodynamic constitutive model is developed to describe the undrained shear behavior of gassy sand. The model considers the dissipation at the mesoscopic level, and the concept of granular temperature is introduced to describe the irreversible deformation of gassy sand. The relationship between the dissipation mechanism of gassy sand and the macroscopic mechanical behavior is established through the migration coefficients and energy density functions. The ability of the model to describe the undrained shear behavior of gassy sand is verified by the numerical simulation of the undrained triaxial shear tests of the remolded Ottawa sand with different degrees of saturation.