液化傾斜地盤中樁基礎受震行為之試驗與分析

Testing and Analysis of Behavior of Single Piles Undergoing Liquefaction-Induced Lateral Spreading

黃梓瑞(Tzu-Jui Huang)

指導教授 ： 邱俊翔

國立臺灣大學/工學院/土木工程學研究所/碩士(2019年)

https://doi.org/10.6342/NTU201900588

摘要

液化土層位於緩坡或靠近水源處而發生大量側向流動之現象，稱為液化側潰。單一液化土層發生液化側潰時，液化土層流動力將對樁基礎造成側向變位及彎矩反應。若樁基礎位於液化土層上覆非液化土層之地盤，非液化土層對樁基礎造成相較於前者更大之流動力，進而對樁基礎造成較單一液化土層情況為嚴重之損害。
本研究利用1-g振動台進行一組液化側潰試驗，試驗使用非液化土層鋪設於液化土層上方之雙層土層，並且擺設兩支不同勁度之鋁樁及聚丙烯樁(Polypropene pile，以下簡稱PP樁)，探討樁基礎位於液化土層上覆非液化土層之地盤情況受側潰之影響。觀察土層位移及水壓記錄，發現土層側潰之發生略早於土壤液化，且依照土層滑移趨勢可將液化側潰分為四個階段，分別為側潰發生之前、主要液化側潰階段、液化側潰後期及側潰結束後。利用移動平均法可將樁身彎矩分離為單向(monotonic)彎矩及反覆振盪(cyclic)彎矩，前者主要是由土層側潰力所影響，後者則由地盤受震反覆運動後所引發之循環應變所控制，觀察兩樁樁身單向彎矩發現側潰力主要是由非液化土層所貢獻，而液化土層之側向力甚小且可忽略。
試驗結束後，利用日本道路橋(JRA)所建議之液化側潰評估方法，對試驗結果進行分析比較，發現JRA之建議公式會高估土層側潰力，其主要差異為JRA建議公式高估了液化及非液化土層所提供之側向力。接著假設非液化土層之側向力為均佈，並忽略液化土層側向力後，建立一簡化擬靜態分析方法，其分析結果驗證液化土層側向力確實可忽略，且樁身彎矩反應主要由非液化土層所控制。

關鍵字

土壤液化 ； 液化側潰 ； 擬靜態分析 ； 雙層土層 ； 振動台試驗

並列摘要

Lateral spreading is a common phenomenon of liquefied ground with a gentle slope or near the waterfront that produces a large amount of lateral soil displacement. For piles subjected to lateral spreading, they may be damaged due to significant bending moments induced by the lateral spreading soil pressure.
In this study, a 1g shaking table test was carried out to investigate the response of piles subjected to lateral spreading. Two single model piles with different stiffnesses (aluminum (AL) and polypropene (PP) piles) embedded in multi-layered sloped ground (2˚) consisting of a liquefiable saturated sand layer overlain by a non-liquefiable dry sand layer were tested. According to soil displacement and water pressure records, the lateral spreading in the test occurred slightly earlier than the soil liquefaction did. The whole development progress of the lateral spreading can be divided into four stages: before lateral spreading, main lateral spreading stage, secondary lateral spreading stage, and after lateral spreading. Using the moving average approach, bending moments in the piles can be divided into monotonic moments (caused by lateral spreading) and cyclic moments (caused by cyclic ground movement). Based on the monotonic moments in AL and PP piles, the lateral soil pressure due to lateral spreading effect were mostly caused by the non-liquefied soil layer, but the influence of the liquefied soil layer can be neglected.
The lateral spreading soil pressure formulas proposed in the specifications of Japan Road Association (JRA method) were further used to predict the lateral spreading soil pressure developed in the test. It was found that the JRA method significantly overestimated the lateral spreading soil pressure induced by the non-liquefied soil layer.

並列關鍵字

soil liquefaction ； lateral spreading ； pseudo-static method ； multi-layered ground ； shaking table test

參考文獻

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