A bounding surface plasticity model for methane hydrate-bearing sediments in deep seabed

This study proposes a new constitutive model to simulate the mechanical behavior of methane hydrate-bearing sediments, by modifying the SANISAND-C model originally designed for sands with low cement content. To capture the distinctive cementation effect of methane hydrate (MH), modifications are made to the state parameter and bonding degradation law of the SANISAND-C model. In addition, the initial bonding strength of MH is not only determined by MH saturation but also by a condition parameter that depends on temperature, pore pressure, and salinity. The densification effect caused by MH pore-filling and grain-coating is captured by replacing the original void ratio in the elastic and plastic moduli of the SANISAND-C model with a reduced void ratio. The model is verified through a comparison of its predictions not only with experimental data but also through discrete element method simulations that cover a wide range of loading paths including drained and undrained true triaxial tests. The model successfully captures the stiffness, strength and dilatancy enhancements induced by MH, as well as the temperature, pore pressure, and salinity-dependent behavior of sediment. Additionally, the model developed can account for different hydrate occurrence habits by adjusting a single parameter related to bonding strength.