為能在擋土結構性能下降但未達破壞前及時掌握而防範於未然，本研究針對常用之重力式與懸臂式擋土牆，量測其微振反應，透過頻譜分析展現牆─土互制系統之動力特性，藉此反映其擋土性能之變化；並引入基於振動之性能指標，藉此具體量化擋土牆性能變化程度。首先，利用有限元素法分析軟體PLAXIS 2D建立擋土牆數值模型，模擬牆趾土壤開挖、基礎土壤弱化、背填土弱化或主動破壞等情境對於擋土牆振動特性之影響；接著，進行室內縮尺模型試驗，以印證數值分析之結果；進一步針對台南市南化區與龍崎區擋土牆案例進行現地量測，驗證所提出方法應用在實際擋土牆之可行性。在數值分析與縮尺模型中，振動顯著頻率與頻譜尖峰振幅之變化能有效展現擋土牆弱化之情形，且性能指標確實有助於量化擋土之性能弱化程度；其中，又以牆趾土壤開挖與背填土弱化之影響較為明顯；現地試驗中，因條件較為複雜，牆體的自然頻率較難以清楚判別，南化區擋土牆案例中，由嚴重開裂牆體振動轉換函數值較輕微開裂者上升之情況，仍有助於展現擋土牆性能弱化之影響。龍崎區擋土牆案例中，能藉由轉換函數頻譜，發現舊有牆體較新建牆體呈現較明顯之高頻振動反應，可能代表其有局部受損之現象；並驗證H/V與平均頻譜等方法於實際應用之成效，證明基於振動之擋土牆性能評估具有實務應用之潛力。

To detect the degradation of retaining structures before failure is caused so that the follow-up slope disasters can be prevented, this study aimed to assess the stabilization performance of the widely used gravity and cantilever retaining walls based on their vibration response, which can reveal the dynamic characteristics of the wall-soil interaction system. In addition, vibration-based performance indices were introduced to quantify the performance variation of retaining walls. The finite element software PLAXIS 2D was used for the numerical simulation of the influences of the excavation beside the toe of the retaining wall, the weakening of foundation soil and the weakening and active failure of backfill on its vibration characteristics. 1/25 scale model tests were conducted to validate the results of finite element analysis (FEA). The practical feasibility of the proposed idea was further examined by the field vibration measurements of retaining walls at two sites in Tainan. The results of both FEA and scale model tests showed that the change of the predominant frequency and the peak amplitude of the vibration spectrum of the wall-soil system helped to exhibit the performance degradation of the retaining wall, and the degradation can be quantified by the use of vulnerability indices. Concerning the field measurements, the natural frequency of the retaining wall was difficult to be clearly identified, yet the more damaged or aged walls generally had more significant response at higher frequencies; the H/V spectral ratio and time-averaging spectrum was also verified effective in characterizing the vibration of the wall. To sum up, the potential of vibration-based performance assessment of retaining walls for engineering practical application was demonstrated.

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