傾斜液化地盤中單樁受側向流動力作用下反應之參數研究

Abstract

當地震引發傾斜液化地盤側潰，位於該地盤中的樁基礎容易受側潰力作用而造成損害。本研究利用陳靖霖 (2021) 發展之分析模式以SAP 2000模擬側潰作用下的樁基礎反應，其中有關液化層的側推力，其大小受到液化土壤黏滯係數影響，另根據Chiou et al. (2023) 所提出之修正方法，以正規化後土壤模型尺寸決定黏滯係數。本研究以前人試驗結果驗證此分析模式的適用性。另以日本現行設計規範與其他學者提出之分析方法模擬前人試驗結果，評估其模擬表現。 本研究以此擬靜力分析模式針對液化地盤上附非液化地盤之側潰地盤中的樁基礎進行一系列參數分析，探討參數包含上部非液化層厚度、樁頭束制、樁徑與土壤側潰位移，研究各參數對樁基礎反應之影響。前人多認為上部非液化層的存在會使樁基礎反應增加，並且隨厚度增加，樁位移、彎矩隨之增加。本研究提出臨界液化地盤厚度，薄液化地盤下的樁基礎反應受上部非液化層控制，樁反應隨上部非液化層厚度增加而增加，厚液化地盤下的樁基礎反應受液化層控制，樁反應隨上部非液化層厚度增加而減少，其原因為液化層側推力會影響上部非液化層下坡側土壤反力，進而影響上部非液化層合力大小，樁基礎反應因而改變。臨界液化地盤厚度之決定係根據上部非液化層所受側潰土壤位移。若側潰位移隨液化層厚度增加而增加、樁頭束制或樁徑增加，均會使臨界液化地盤厚度增加，實務上樁基礎受到上部非液化層厚度影響多為薄液化地盤情況下的反應趨勢。

When an earthquake triggers lateral spreading and slope failure in liquefied ground, the pile foundation located within that ground is susceptible to damage from the lateral spreading forces. This study utilizes the analytical model developed by Chen (2021) and simulates the response of pile foundations under lateral spreading using SAP 2000. The lateral spreading force related to the liquefied layer is influenced by the viscous coefficient of the liquefied soil, which is determined based on the normalized soil model dimensions as proposed by Chiou et al. (2023). The applicability of this analytical model is validated using previous experimental results. Additionally, the study employs the current Japanese design codes and other analytical methods proposed by scholars to simulate the results of previous experiments, assessing their simulation performance. A parametric analysis of pile in lateral spreading ground is conducted, investigating the impact of parameters, including the thickness of non-liquefied layer, pile cap restraint, pile diameter, and lateral spreading displacement. Critical thickness of liquefaction layer is determined by the lateral spreading displacement. For thin liquefied ground, the pile response is controlled by the non-liquefied layer, with pile response increasing as the non-liquefied layer thickness increases. In contrast, for thick liquefied ground, the pile response is governed by the liquefied layer, with pile response decreasing as the non-liquefied layer thickness increases. Lateral spreading force from the liquefied layer affects the downslope soil reaction, influencing the overall force equilibrium and altering the pile's response. The influence of the non-liquefied layer thickness is primarily observed in the context of thin liquefied ground in practical scenarios.