摘要 地震發生時，基礎鬆散飽和砂土液化會造成路堤結構物的沉陷、側向滑動與堤頂開裂等破壞現象。目前較新的研究已使用動態數值程式來模擬路堤震後之變形破壞行為，所得成果相當豐碩；但是有鑒於動力分析為有效應力分析法，必須建立複雜之土壤動力組成模式，所需分析程序繁複且動態參數不易取得，因此，有必要建立一套工程上較容易應用的液化變形分析方法。本研究使用二維顯性差分程式FLAC，利用擬靜態將土壤強度參數弱化的觀念模擬基礎土壤受震液化過程，以探討路堤受震的變形破壞機制。分析結果顯示，利用擬靜態液化變形分析所得之路堤變形機制與動態離心試驗相似，因此使用此分析法可以大致掌握路堤受震變形行為，且發現路堤震後變形量會受到基礎土壤分佈型式、路堤高度與河岸地形等因素影響。在掌握路堤受震變形行為與沉陷量之後，必須提出有效的抗液化對策以降低基礎土壤液化所造成的沉陷與破壞。本研究針對鋼版樁加繫纜圍束、深層攪拌工法與高壓噴射灌漿工法，利用擬靜態液化變形分析法模擬基礎土壤液化，以檢核不同抗液化對策與配置方式之成效。分析結果發現，在路堤兩側堤趾下針對液化土層進行全深度高壓噴射灌漿改良，可以大幅度降低路堤的沉陷量與抑制路堤結構之變形，抗液化成效顯著；深層攪拌改良之抗液化成效亦十分明顯；而鋼版樁圍束必須加設繫纜才能有效降低震後沉陷量。利用擬靜態液化變形進行分析是將所有液化土層皆弱化至相同抗剪強度，然而砂土之液化程度與初始剪應力比有關，本研究發現初始剪應力比分佈範圍會受到路堤幾何形狀與基礎土壤強度參數的影響。研究結果顯示利用擬靜態液化變形分析法，可以大致掌握路堤因基礎土壤液化所造成的變形破壞行為，並且可以探討不同液化防治對策、配置方式與範圍之抗液化成效，可供工程界作為設計路堤液化對策之參考。 ABSTRACT During earthquake, foundation soils liquefaction will cause settlement, lateral spreading and crest crack of an embankment. Recently, dynamic effective stress methods have been developed to simulate complex -liquefaction deformation behavior of an embankment. However, due to the difficulties in obtaining the relevant soil parameters and computing effort. it was recommended to establish a simplified liquefaction deformation method for use in engineering practice. Based on softening strength parameters of foundation sandy soil to simulate the liquefaction effect, this study uses 2D explicit difference program FLAC to analyze statically the post-liquefaction behavior of an embankment. The numerical results seem to be roughly consistent with the results of the dynamic centrifuge experiments. Moreover, the liquefaction-induced settlement is influenced by foundation soil types, embankment height and river topography. After the investigation of past-liquefaction deformation behavior, the effectiveness of three countermeasures is evaluated for use in preventing liquefaction of the foundation soils. Numerical results show that the use of jet grouted soilcrete at both toes of the embankment is most efficient in confining liquefied foundation soil and in reducing the post-liquefaction deformation of embankment; the effectiveness of deep mixing method is also great; however, the sheet piles can not efficiently confine foundation soil without a high-tension tie rod. In the proposed methodology, the undrained strength of all liquefiable soils was softening to the same degree; however the softening degree due to liquefaction is dependent on initial static shear stress ratio of foundation soil. This study shows that the ratio is influenced by the geometry shape of embankment and strength parameters of foundation soil.
