本研究應用一套以Biot多孔介質變形理論為基礎，非線性行為以帽蓋模式及Pacheco孔隙水壓模式為架構，搭配黏滯邊界元素之三維有限元素分析程式，設計一系列含單一粉土夾層的砂質土層模型進行數值分析，藉以探討不同粉土層位置及其厚度對整體液化行為之影響。 研究結果顯示：(1)若砂土層中含單一粉土夾層時，粉土層之存在可縮小達液化之範圍，並減小沉陷量；(2)若粉土夾層位置接近地表，則粉土層下方之土層，因孔隙水無法傳遞，故粉土層下方易累積過量之超額孔隙水壓，非但容易產生砂湧，更延長了整體土層之水壓消散時間，造成土層於振動後不穩定時間長；(3)若粉土夾層位置於較深層，則上述之狀況可有明顯的改善。 In this study, an effective stress based three dimensional finite element model is adopted to investigate the ground motion of a sandy deposits with a thin silt intra-layer at various depths. The nonlinearity of soil is assumed to follow the Cap model, and the pore pressure model based on Cap model, developed by Pacheco, is adopted to simulate the built-up of the pore pressure. The conclusion drawn from this studies are as follow: (a) the thin silt intra-layer in the sand deposit can reduce the extent of liquefaction and the surface settlement; (b) liquefaction occurs only in the sand beneath the thin silt layers near the surface. The ratio of the excess pore water pressure is larger than one in the sand just beneath the silt layer; (c) for the deeper thin silt intra-layer, liquefaction occurs not only in the sand beneath the thin silt layers but also in the sand near the surface; (d) the sand deposits with shallower thin silt intra-layer is danger.
