Abstract: Gas hydrate bearing sediments can be regarded as a composite material composed of matrix phase (soil particles, pore water and gas) and inclusion phase (pure hydrate crystals). In this paper, the multi-scale method that is commonly used in the field of composite materials research was adopted to study the mechanical properties of gas hydrate bearing sediments. The constitutive relationship between the matrix and hydrate phases was characterized by the critical state elastoplastic-constitutive model related to the sand state and the elastic-brittle model, respectively. Meanwhile, the factor of hydrate activity was introduced to represent the slip and fracture of hydrate crystals during the triaxial shearing process the proportion of hydrate crystals which can bear the load effectively in the deformation process. Based on Eshelby’s equivalent inclusion theory and Mori-Tanaka method in the meso-mechanics theory, the equivalent elastoplastic stiffness matrix of gas hydrate bearing sediments was derived. And then, an elastoplastic constitutive model of gas hydrate bearing sediments was established considering the occurrence mode, strength, strain softening and dilatancy of gas hydrate bearing sediments under different confining pressures, different gas hydrate bearing sediments contents and different hydrate occurrence modes. The physical meaning of the proposed model was clear, the form was simple, and all the parameters included in the proposed model were easy to be obtained through simple laboratory tests. Finally, the model was verified by the existing experiments data. The results show that the proposed model can well describe the mechanical properties of gas hydrate bearing sediments under different test conditions.

Key words: gas hydrate bearing sediments, homogenization theory, elastoplasticity, constitutive model