三维离散元单轴试验模拟甲烷水合物宏观三轴强度特性

填充型水合物的砂性能源土试样可视为特殊的散粒体材料,即砂粒和水合物颗粒混合物,具有明显的非连续特征。为研究填充型水合物的能源土力学特性,初步探索了甲烷水合物在不同温度、反压条件下加荷模式的离散元模拟方法。离散元模拟中,将水合物块体视为由大量颗粒通过强胶结作用凝聚而成的整体,室内试验中的内部孔隙水压作用转化为水合物颗粒间的胶结力,故需要合理确定颗粒间胶结模型参数来实现反压的影响作用。通过参数反演建立了宏观强度、刚度参数与平行胶结模型的微观胶结参数间的宏、微观关系,基于已有室内甲烷水合物三轴试验资料,确定了给定温度和反压条件下的微观胶结参数取值,随后进行离散元单轴压缩试验。离散元单轴压缩试验模拟获得的水合物强度特性,与室内三轴试验结果符合较好;通过建立的宏、微观参数间的关系,实现了不同温度、反压下的水合物加荷模式的模拟。为进一步提出深海能源土离散元数值试验成样方法——孔隙填充水合物生成技术,形成含填充型水合物的能源土试样,研究其力学和变形特性奠定基础。

Three-dimensional distinct element simulation of macro triaxial compressional strength characteristics of methane hydrate through uniaxial compressional test

Marine sandy sediments containing pore-filling type methane hydrate particles can be considered as a class of special granular materials which present apparent discontinuity characteristics. In order to investigate the mechanical characteristics of methane hydrate-bearing sediment (MHBS), the paper preliminarily explores the simulation method about the load mode of methane hydrate under the different temperatures and confining pressures. To numerically simulate such materials, the distinct element method (DEM) can be used by modeling methane hydrate particles as groups of spheres cemented together and filled into the pores of soil skeleton. The back pressure is converted into inter-particle cementation, and it is rational to choose appropriate parameters of inter-particle bond model to realize the role of back pressure. The macro-micro parameter relation among macro-strength, macro-stiffness parameters, microscopic cementation strength and stiffness parameters of parallel bond model is established, based on existing indoor triaxial compression test of methane hydrate. The cementation parameters of parallel bond are determined under the condition of a given temperature and pressure state. The deviator stress obtained from the stress-strain behavior of methane hydrate uniaxial tests in DEM simulation is in line with that of the laboratory triaxial compressional tests. The relationship between macro-micro parameters can be used to realize the simulation about the load mode of methane hydrate by DEM. This study lays foundation to further propose a technique for generating pore-filling methane hydrate-bearing sediments and to study the mechanics and deformation characteristics of MHBS.