921集集地震曾造成台灣多處地區有土壤液化和基礎破壞現象，土壤液化不但會產生地盤側向滑動與地層下陷，同時亦對地層內之基礎造成嚴重影響。本研究採用員林地區液化鑽探資料與測站之地震紀錄，依規範所建議之土壤液化評估法分析其土質折減係數，並將此折減係數施用於土壤模數值，並配合土壤彈簧模式分析自由場之地盤液化反應，再將地盤反應作用於可模擬樁基礎之波動方程解，以分析液化地盤內樁基行為。研究發現：液化下之土質折減係數分析將不致改變最大地表位移和樁體變形量，但其將使液化區土層的位移和樁體的變形和彎矩放大，衍生破壞。無論土壤液化與否，大型地震均將致使樁基頂部產生過量之彎矩和剪力，造成混凝土開裂進一步產生彎矩破壞並致使樁基被剪斷。 The Chi-Chi Earthquake causes soil liquefactions and foundation damages at many sites in Taiwan. Soil liquefaction not only can yield lateral spreading and ground settlement, but also produce severe impacts onto the foundations. This study presents the analysis for pile foundation subjected to the liquefied soils. Bored hole data from the Yuan-Lin area and the corresponding seismic records are used to obtain first the soil reduction factors as those suggested in code for evaluating liquefaction potential. These reduction factors were applied to the soil modulus and the associated spring model for free-field seismic response of the site under the earthquake. The ground motions were then mounted to the piles for corresponding foundation responses. The results showed that the ground displacements and pile deformations would not be affected much by the reduction factors of the soil parameters in the liquefaction analysis, however it could yield larger soil displacements and pile deformations as well as bigger moments along the piles at the liquefied layers. No matter the soil liquefies or not, large earthquake would result in excessive moments and shears for the pile head in which the concrete pile may fails to moments and shears.