SANISAND-CH: A high-pressure bounding surface model for cemented sand, including methane hydrate-bearing sediments

This paper introduces anew constitutive model capable of predicting both the shear and compressive stress response of common cemented sand and methane hydrate-bearing sediments (MHBS) under high pressures. This model extends the SANISAND-H model, which is designed for the high-pressure response of clean sand, and incorporates specific constitutive elements from the SANISAND-C model, tailored for cemented sand under normal stress levels. It refines the narrow, closed conical yield surface of the SANISAND-H model by incorporating a bonding strength variable that diminishes with plastic strains. Furthermore, it modifies the critical state lines, reference compression curve, elastic parameters, state parameter, flow rule, and hardening law of SANISAND-H model to account for the cementing and densifying effects of cementitious materials. To capture the effects of temperature, pore pressure, and salinity on the behavior of MHBS, the model includes a condition parameter, influencing the critical state and bonding strength. Validation through laboratory tests confirms the model's accuracy in simulating the enhanced shear strength, dilatancy, and softening behavior, as well as the reduced compressibility of cemented sand. Moreover, it accurately captures the mechanical responses induced by particle crushing under high pressures.