921集集大地震之芮式規模高達7.3,不僅對橋樑和建築結構等造成重創外,地震當時,台灣中部更有許多地方產生土壤液化現象,其中又以員林地區之大區域土壤液化最為嚴重且最廣為人知,而現場之液化現象包括有地表噴砂、地層下陷、建築物沉陷、建築物傾斜和溝渠等構造物水平側移等。本文將以員林地區集集大地震之液化評估為例,介紹土壤液化之評估流程與方法,包括現場之地質調查結果以及液化潛能之回饋分析,經比較SPT-N法和CPT法所計算出之液化潛能指數,其變化趨勢雖然類似,但數值差異卻很大,整體而言,以Seed方法配合液化潛能指數(P(subscript L))的評估結果與現地液化表徵的分布最為一致,即在本次員林地區集集大地震案例回饋分析中的表現最佳。
Chi-chi earthquake, with a magnitude of 7.3 (Ritcher scale), not only caused severe damages to bridges and buildings, but also resulted in soil liquefaction in many areas in central Taiwan. The Yuan-Lin in Chang-Hua County suffered extensive damages, including soil liquefaction, subsidence, settlement and tilt of buildings, lateral movement of ditches, etc.This article presents the process and analysis methods for liquefaction during Chi-Chi earthquake in Yuan-Lin, including site investigation and back analysis result. The liquefaction potential using SPT method and CPT method varies a lot, but the tendency is quite similar. Generally speaking, the results calculated by Seed's method incorporated with liquefaction potential index well match the field evidence caused by liquefaction. It is considered that Seed's method is the most suitable one in this study of liquefaction in Yuan-Lin in Chi-Chi earthquake.