樁基礎受液化和地盤側向流動之結構行為分析

機構典藏 > College of Engineering > Graduate Institute & Department of Civil Engineering > Thesis > Item 987654321/34520

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Title:	樁基礎受液化和地盤側向流動之結構行為分析
Other Titles:	Structural analysis for pile foundations subjected to soil liquefaction and lateral spreading
Authors:	林伯勳;Lin, Bor-shiun
Contributors:	淡江大學土木工程學系博士班張德文;Chang, Der-wen
Keywords:	樁基;波動方程;液化;流動地盤;pile foundations;wave equation;soil liquefaction;lateral spreading
Date:	2006
Issue Date:	2010-01-11 05:20:45 (UTC+8)
Abstract:	樁基礎結構耐震行為常受工程界所重視，有關研究亦為土壤動力和土壤結構互制學域的重點項目之一。基樁之動力行為常用於有限元素分析法，由於該項方法相對複雜，資料準備和輸入均不易，故亦未能被普及運用；鑑於此，發展一簡易且具效率性動力分析程式遂有其必要性。本研究以樁基波動方程做為分析主軸，結合土壤液化與流動地盤之不同模擬方式，開發一套簡易動力分析程序EQWEAP，以有效地處置液化與流動地盤所衍生之工程問題，並與實際案例比較以了解基樁反應和結構破壞機制，供樁基礎設計分析參考。有關液化分析方面，本研究採用土質參數折減與孔隙水壓模式進行模擬，其優點在於能瞭解樁體與土體之同步性歷時反應，並適用於基礎結構物位於平坦地形之現場，地盤僅有液化而無流動之虞所造成的基礎反應。研究發現兩者所得樁身最大位移發生位置並不一致，前者發生於液化土層，後者則發生於地表，然所預測的位移量均在合理範圍，其中由於土質參數折減分析之土壤參數需進行經驗化評估，且與現場土壤之標準試驗貫入值有關，本研究仍建議以孔隙水壓模式分析進行模擬，以避免前項分析過於簡化和需土壤模數率定所可能產生的困擾。對於流動地盤之分析，本研究採用擬動態土壓力與傳統靜力法進行分析，其優點在於設定參數簡易且分析具有效率，不需進行自由場分析即可直接以波動方程進行求解。該項分析方式適用於鄰近河岸或水際線以及位於緩坡之樁基礎，以模擬遭受地盤流動影響之結構反應與破壞機制。研究發現兩者所得樁身最大位移量發生位置和整體樁身最大變形型式亦非完全一致，前者最大位移發生於樁底，後者最大位移則發生於樁頂，然最大位移亦均在合理範圍。其中擬動態土壓可納入時間和垂直地震影響因素，對於地震歷時中所產生的深層破壞或大範圍流動的影響，應能有效掌握；而靜力分析之土壓力和地盤反力等模式可有效地模擬地震所造成之淺層流動破壞影響。該項觀察與地盤流動之發生機制、地形因素有明顯關聯，分析者必須掌握現地質條件以決定使用方法。 Seismic behaviors of pile structures are vital for geotechnical engineering. With regard to this topic, researches are mainly involved with soil dynamic and soil structure interaction. Finite element method is often implemented to analyze dynamic pile response. Due to the complexity of methodology and data preparation, it would not be employed commonly. In view of the above points, it is necessary to develop a simplified and effective dynamic program. This study suggested a simplified dynamic procedure termed as EQWEAP, based on wave equation and incorporating with different models of soil liquefaction and lateral spreading. Case studies would be conducted to realize responses of piles and structural failure mechanism, and to provide some useful information in practice. In soil liquefaction analysis, this study adopted reduction factors and pore pressure model. Its advantages lie in monitoring the simultaneous responses of piles and soils and it could be applied where foundation structures located in level ground, which only liquefied and not occurred flow failure. It is found that maximum pile displacements of both methods took place unequally, but the predicted displacements consisted in rational ranges. The former occurred in liquefied soil layer, and the latter occurred at the pile head. Because the reduction factors model need the empirical assessment from SPT-N values to get the soil parameters, this study suggested the pore pressure model primarily to conduct soil liquefaction problems for avoiding the possible errors from the prior. In lateral spreading analysis, the study adopted pseudo dynamic earth pressure and traditional static models. Those would not only simply define the parameters of soils and have an explicit numerical procedure to effectively obtain the solutions, but it could analyze the pile deformations directly by wave equation and not proceed the free field analysis. Those applied to simulate the mechanism of offshore pile foundations and pile foundations on the gentle slop subjected to lateral spreading. The positions of maximum pile displacement and the deformed shapes of the whole pile body from the both methods are not similar. The former occurred at the pile head, and the latter occurred at the pile tip. The former could include the time effects and vertical earthquake acceleration and could effectively master the deep failure of soil stratum or large lateral spreading range during earthquake. The latter could effectively simulate the shallow failure induced by lateral spreading after earthquake. These observations are related significantly to the occurrence of mechanism by lateral spreading and landforms in situ. The one should know well soil profiles to determine the proper method to analyze.
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