地震引致之土壤液化現象將導致砂質土層強度與勁度顯著降低，進而影響基礎構造物之耐震性能。雖然我國現行建築物基礎構造設計規範建議了液化地層之土壤參數折減係數，然其僅適用於抗液化安全係數(F_L)小於1之情況，對於F_L大於1但仍有超額孔隙水壓激發之情境則未予以涵蓋。為能合理掌握地震時具液化潛能砂質地盤中基樁之側向承載能力，本研究透過縮尺物理模型試驗，在不同超額孔隙水壓激發程度(以超額孔隙水壓比 r_u 代表之)下對飽和砂土地盤中模型樁之樁頭進行反覆側向加載；其中，為能精準達到目標 r_u 值，係採用向上滲流來引發超額孔隙水壓。試驗中量測樁身撓曲應變，並藉由多項式回歸擬合彎矩函數，進而求取樁身之剪力、土壤反力與側向位移分佈，探討樁周土壤側向阻抗在液化過程中之變化趨勢。結果顯示，當 r_u 接近1時，土壤提供之反力顯著降低，且側向承載能力明顯衰退，展現液化土層對基樁耐震性能之負面影響。進一步建立不同深度下之土壤反力~側向位移關係，即所謂之p-y曲線，觀察其於超額孔隙水壓激發時之弱化情況，並歸納p-y曲線斜率(即水平向地盤反力係數)折減程度與r_u之關係，據以補足現行規範所建議折減係數不足之處。研究成果有助於合理掌握液化地盤中基樁之側向承載能力，可做為基礎耐震設計與耐震能力評估之參考，有助於提升地震災害下基礎系統之安全性。

In this study, scaled physical model tests were conducted to better understand the lateral bearing capacity of piles in liquefiable ground during earthquakes. In these tests, displacement-controlled cyclic lateral loading was applied to the model piles embedded in saturated sand. The sand was subjected to various degrees of excess pore pressure buildup (represented by the excess pore pressure ratio, r_u ) induced by controlled upward seepage. The flexural strain distributions along the model pile were measured, and polynomial regression was used to fit the bending moment profiles. Based on the polynomial moment functions, the distributions of the soil reaction (p) and lateral displacement (y) were further deduced to investigate the degradation of lateral soil resistance during the liquefaction process. The results show that the soil reaction decreases significantly as r_(u )approaches 1, leading to a notable reduction in lateral bearing capacity of the pile. This highlights the detrimental effects of liquefaction on the seismic performance of piles. The relationships between soil reaction and lateral displacement (so-called p–y curves) at different depths were further established. The degradation of p-y curves under different degrees of excess pore pressure was observed. Accordingly the reduction in the coefficients of horizontal subgrade reaction (i.e., the secant stiffness of the p–y curve) was correlated with r_u , which helps to fix the insufficiency of current design code in Taiwan. These findings provide practical insights for the seismic design and performance assessment of foundations.

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