ADVANCES IN MICROMECHANICAL PROPERTIES OF HYDRATE-BEARING SOILS

As one kind of clean and unconventional energy resources, natural gas hydrates have drew enormous interests worldwide due to their high energy density, large reserves, and wide distribution in nature, and lots of countries have tried their best to develop suitable methods for gas hydrate production with acceptable safety, efficiency, continuity, and controllability. Industrialized production of gas hydrates basically needs to deeply understand mechanical properties of hydrate-bearing soils and fully clarify how these mechanical properties evolve during gas hydrate production. Mechanical properties of hydrate-bearing soils are inherently governed by their micro structures inside, and great efforts have been made to study macro mechanical properties of hydrate-bearing soils from the micro perspective, which is of great significance to deep understandings of how mechanical properties of hydrate-bearing soils evolve during gas hydrate production. In this study, advances in mechanical properties of gas hydrate crystal, interface cementation between gas hydrate and soil particles, and bulk hydrate-bearing soils are summarized. Gas hydrate crystal structures and pore-scale hydrate morphologies in hydrate-bearing soils are briefly introduced. Then, fundamental principles and advantages of microscopic testing techniques such as computed tomography (CT), scanning electron microscopy (SEM), X-ray powder diffraction (XRD), and atomic force microscopy (AFM) applied to mechanical property characterizations are emphasized. Then, up-to-date researches performed by using triaxial shearing tests combined with CT, particle flow code (PFC) and molecular dynamics (MD) numerical simulations are reviewed, and the shearing mechanism as well as constitutive models of hydrate-bearing soils are analyzed. At last, challenges in current studies on micromechanical properties of hydrate-bearing soils are discussed, and corresponding suggestions are subsequently proposed to further studies on mechanical properties of hydrate-bearing sediments.