柔性边界三轴压缩条件下胶结型水合物沉积物力学特性的离散元模拟

DEM simulation of triaxial test on cementing type gas hydrate-bearing sediments under flexible boundary condition

首先,提出了一种胶结型水合物沉积物离散元试样的生成方法,并采用FLAC3D和PFC3D耦合方法创建了侧面柔性边界条件,生成了不同饱和度的水合物试样;其次,考虑水合物的胶结效应,引入线性平行胶结模型并由室内试验结果标定了接触模型参数;第三,根据数值模拟结果分析了水合物沉积物的强度和变形破坏特性;最后,从力链和能量角度揭示了水合物在应力传递中的微细观力学机制。研究结果表明:建立的离散元模型能准确计算柔性边界条件下的试样体积变化,其模拟结果与室内试验结果吻合较好;水合物沉积物的黏聚力随着水合物饱和度增加而增大,其内摩擦角与水合物饱和度的关系不大;水合物饱和度对水合物沉积物的应变局部化特征影响很大;水合物颗粒参与力链的形成与演化,水合物饱和度越大,高应力水合物颗粒数目越多,水合物颗粒在力链中占比越大;水合物沉积物的弹性应变能、胶结应变能和摩擦耗能的存储和耗散主要通过砂土与水合物间的接触演化作用完成。

Firstly,the discrete element method(DEM)was used to simulate the macroscopic mechanical responses of cementing type gas hydrate-bearing sediments(GHBS),in which the linear parallel bond contact model was adopted considering hydrate cementing effect.Secondly,the linear parallel bond model was introduced considering the cementing effect of hydrate,and then the parameters of the contact models were calibrated based on laboratory test results.Thirdly,the strength and deformation characteristics of GHBS were investigated based on the simulation results.Finally,the role of hydrates played in stress transmission was revealed in terms of force chain and energy.The results show that the developed DEM model can accurately calculate the volume change of a sample under the flexible boundary condition.The simulation results are in good agreement with the laboratory test results.The cohesion of GHBS increases with the increase of hydrate saturation,while its internal friction angle is independent of hydrate saturation.Hydrate saturation has great influence on the strain localization of GHBS.Hydrate particles play an important role in the formation and evolution of force chain.The higher the hydrate saturation,the greater the number of high stress hydrate particles and the larger the proportion of hydrate particles in the force chain.The elastic strain energy,cement strain energy and friction energy in GHBS are stored and dissipated mainly due to the contact between sand and hydrate and its evolution.