三维离散元法解析砂型泥石流细观运动特征研究

Analysis on Mesoscopic Movement Characteristic of Sandy Debris Flow by 3D Discrete Element

基于散体介质理论的三维离散元数值分析方法,引入粘滞阻尼模型考虑系统耗能效应,求解固体作用力和流体连续性方程,充分考虑流固耦合作用,对中、细标准砂泥石流过程进行仿真分析,得到不同砂型泥石流破坏过程及渗流场、颗粒速度场、孔隙率、颗粒接触数等参数变化规律。分析表明,中砂、细砂分别表现出分层渐进式和流滑型的破坏模式,这与已有物理试验现象吻合,验证该模型的适用性,并从渗流场分布规律深刻解释该现象发生机理。泥石流过程中土颗粒速度矢量变化规律从细观上揭示了隐藏在颗粒内部的相互碰撞、摩擦、滑动等复杂运动特点,从宏观上揭示了中砂土坡脚薄弱位置率先突破,主滑动体形成直至完全失稳的分级渐进式破坏过程。进一步分析了土体孔隙率和平均接触数分布云图变化规律,中砂泥石流过程中随颗粒运动,滑动体孔隙率逐渐增大,颗粒接触数逐渐减小,并且这种发展趋势逐渐往坡后方土体蔓延;进一步揭示了中砂泥石流分级渐进破坏过程与颗粒速度场分析规律一致。分析结果表明了该模型方法在模拟泥石流这种大变形、流固耦合问题上的适用性,这对泥石流复杂机理的更深入探索是有益的。

Based on the theory of three-dimensional discrete element numerical method,by introducing the viscous damping model considering the system energy dissipation effect and solving the solid force and fluid continuity equation with full consideration of fluid-solid coupling,the medium and fine sand debris flow are simulated,different landslide failure process of sand and seepage field,particle velocity,porosity,average contact number of particles are got. Analysis indicates the medium sand,fine sand show layered progressive failure mode and streaming-slip failure mode respectively,which is consistent with the physical tests phenomenon. The applicability of the model was verified,and then the macro phenomenon mechanism of landslides was explained profoundly from the distribution law of seepage field. The particle velocity vector changing law reveals the complex motion characteristics of mutual collision,friction,sliding and etc hidden inside the soil particles during the landslides from the mesoscopic view,reveals the first breakthrough of weak position of slope foot,and then the formation of main sliding body until the complete destabilization,namely hierarchical progressive failure process in macro. Further analysis of changing law of porosity and average contact number distribution cloud was done to reveal the failure process. In the process of medium sand debris flow,with the soil particles movement,the porosity of sliding body increases and the average contact number of particles in sliding body decreases gradually,and the trend gradually spreads toward the rear slope soil. It further reveals the progressive failure process in the medium sand,and is consistent with the analysis of particles velocity. The results demonstrate the applicability of this simulation method in dealing with the topics such as landslides taking account of large deformation and fluid-solid interaction,and it is beneficial to explore the complex mechanism of landslides further.