侷限固定邊界中顆粒振動對水壓造成之影響

Abstract

在土壤液化中上升的孔隙水壓扮演了重要的角色。雖然已有諸多理論推測振動時孔隙水壓上升的原因並以實驗佐證，但因水壓上升為瞬間之行為，難以在實驗時進行觀察或量測。本研究為探討振動發生時孔隙水壓上升之原因而提出一侷限固定邊界之振動模型，以晶格波茲曼法(Lattice Boltzmann Method, LBM)計算不可壓縮黏性流場，以離散元素法(Discrete Element Method, DEM)計算固體顆粒之行為及有效應力，並以體積積分函數(volume fraction function)型式的沉浸邊界法(Immersed Boundary Method, IBM)定義流固耦合之邊界。經由模擬及分析後發現水壓上升的原因主要為流體被顆粒擠壓出顆粒之間的孔隙而造成，且侷限顆粒向上發展會使水壓隨深度的變異被消除。水壓和顆粒之間有明顯的交互作用。

The increase of pore water pressure is the critical condition of liquefaction. Though there are theories and inference for the reason why the pore water pressure increases during vibration with experiment to prove it, it is difficult to observe or measure the immediate increase of pore water pressure. A vibration model with fixed constraining boundaries is proposed in this study to discuss the reason of increasing pressure. The fluid is solved by Lattice Boltzmann Method and the behavior of particles is solved by Discrete Element Method. The two phases coupling boundary is defined by Direct-forcing Immersed Boundary-LBM in Volume Fraction Function. The result shows that the increasing of pressure is caused by the drainage from the gathering particles during vibration. Also, constraining the particles from upward moving will dispel the difference between behavior of particles with depth. The interaction between particles and water pressure can be observed in the model.