Abstract: The extraction of methane hydrate in the seabed will result in a series of geotechnical engineering problems and disasters. In order to ensure the safety of the related engineering facilities during the extraction, it is necessary to build reasonable constitutive model for methane hydrate bearing sediments. Based on the thorough study of the geomechanical characteristics of hydrate bearing sediments and the contacts between soil grains, the authors suppose that the geomechanical behavior of hydrate bearing sediments resulting from the combination of the friction between soil grains and cementation due to methane hydrate. Considering the different mechanical mechanisms of the friction and cementation, the modified Cam-clay model and elasticity damage model are employed to describe their mechanical responses respectively. By assuming that soil skeleton and cementation have the same strain during the loading, a constitutive model coupling elastoplasticity and damage for methane hydrate bearing sediments is then established based on a simplified damage evolution law. The calculated results are compared with the experimental data of methane hydrate bearing sediments with different hydrate saturations. It is shown that the proposed model can describe the stress-strain behavior of methane hydrate bearing sediments quite well, which demonstrates the validity and reasonability of this model.

Key words: methane hydrate bearing sediments, modified Cam-clay model, damage, constitutive model