MSDM-MHBS: A novel multi-scale damage constitutive model for methane hydrate-bearing sediments considering the influence of fine content and hydrate saturation

The presence of methane hydrates (MH) and fine-grained materials introduces complex mechanical behaviors in methane hydrate-bearing sediments (MHBS), such as pronounced non-linearity and significant strain-softening characteristics. This study proposes a three-step homogenization procedure for the elastic parameters of bonded elements in MHBS, accounting for the effects of microscopic composition with varying mechanical properties and porosity. Moving from the mesoscopic to the macroscopic scale, and following the binary medium concept (BMC), external loading is jointly borne by mesoscopic bonded elements and frictional elements. The mechanical behavior of bonded elements is modelled using an elastic-brittleness framework, while frictional elements are described by the hyperbolic Duncan-Chang model. This approach enables a detailed analysis of the mesoscale deformation mechanisms in MHBS. A multi-scale damage model for MHBS (MSDM-MHBS) is then proposed, integrating the effects of micro-components and mesoscopic deformation mechanisms. The physical significance of the model parameters is explored by comparing the stress partitioning and damage evolution within MHBS. The validity and practicality of the proposed multi-scale damage constitutive model are confirmed through comparison with triaxial compression test results on MHBS with varying fine content and MH saturation. The MSDM-MHBS effectively models the nonlinearity, strain-hardening, and strain-softening characteristics influenced by the presence of methane hydrate and fine-grained particles. Moreover, it establishes a cross-scale relationship without introducing additional model parameters, offering valuable insights into the deformation mechanisms of MHBS and providing a theoretical foundation for the safe exploitation of methane hydrate in future research.