Abstract: Hydrates are often filled in the pores of sediment soil particles or bonded between grain contacts, which have filling or bonding effects on sediments. These formation patterns of hydrate change the original void ratio and density of soil, which significantly affect the physical and mechanical properties of sediments, so it is necessary to consider the effects of hydrate filling and bonding to describe the mechanical properties of hydrate-bearing sediments. In this paper, the equivalent hydrate ratio was proposed to reflect the filling effect of hydrate based on the unified critical state constitutive model for both clay and sand (clay and sand model, referred to as CASM) and combined with the densification characteristics of hydrate intrusion pores. The cohesive strength was introduced to reflect the cementation of hydrates on sediments. Furthermore, an elastoplastic constitutive model for hydrate-bearing sediments was established to describe the hydrate filling and bonding effect by using the state parameters to reflect the stress state and the dilatancy of the soil and adopting the non-associated flow rule. The comparison between laboratory test results and presented constitutive models shows that this model can effectively simulate the stress-strain relationship of hydrate-bearing sediments, and reasonably describe the influence of hydrate content and effective confining pressure on the mechanical properties of sediments, such as strength, stiffness, dilatancy, and so on.

Key words: hydrate-bearing sediments, hydrate content, constitutive model, dilatancy, clay and sand model (CASM)