雙楔形滑動塊體法應用於土釘邊坡之受震分析

本文以雙楔型模式搭配Newmark滑動塊體法，分析土釘加勁邊坡受震滑移的行為。模式中考慮土壤摩擦角隨剪位移增加而衰減，分析的結果與陳建仁(2002)之振動台試驗比較，以佐證理論模式的正確性。另外，亦提出上部塊體變形行為的初步探討，由前幾階段振動之塊體變形分析與試驗結果比對，反推塊體變形分析中適當的彈簧折減勁度，以及預測震後坡面變形的決定方式。研究結果顯示，利用雙楔型滑動塊體法分析土釘邊坡受震產生的滑移量，於最接近平移式破壞之邊坡(模型1)，分析結果最為良好；其餘較為接近傾覆式破壞之模型，分析結果除模型3外，皆較試驗值低。但可發現考量土壤摩擦角衰減於分析模式中，有助於改善瀕臨破壞階段的分析結果。整體而言，滑移量分析與試驗結果有相同的趨勢。於坡面變形方面，基於結構互制原理建立塊體變形模式，於瀕臨破壞階段前亦有不錯的模擬結果，當邊坡受震進入瀕臨破壞階段，由於邊坡已產生較大的變形量，強度大不如前且不易掌握，此時分析結果較為低估。參數研究中，依據Hong等人(2005)所提出模型邊坡與原型間的系統相似律關係，配合前人建議的臨界滑移量觀念，求得60°~90°陡坡於不同地震力作用下所需的最小釘長。此外，基於最小滑移量的原則選擇邊坡的最佳土釘傾角，經分析邊坡坡度為60°、70 °、80°及90°之最佳土釘傾角分別為48°、43°、37°及25°，亦即，邊坡坡度越陡最佳土釘傾角越緩。最後，觀察土壤阻尼比與彈性模數於塊體動態行為分析中，對上塊體相對變形量與延遲現象的影響。

關鍵字

土釘陡坡；地震；雙楔形破壞模式； Newmark法；最佳傾角

並列摘要

This study applies Newmark method with two wedge failure mode to analyze the sliding behavior of steep nailed-slops under seismic excitation. The analytic model has considering decay of the soil internal frictional angle when occur lager shear displacement. In order to confirm the validity of the mode, results of the present study are compared with those obtained from shaking table tests (Chen, 2002). A preliminary discussion regarding the deformation of upper block is also proposed. By comparing preceding steps of analytic block deformation with experimental observations, proper stiffness attenuation in the analysis can be obtained. Analytic results showed that prediction of two wedge sliding block method from the present study and those of shaking table test have good agreement when the nailed slopes belong to translation failure mode (model 1). The results underestimate displacement of sliding block when the nailed slopes tend to rocking failure mode except model 3. Due to incremental sliding shear displacement considering the decay of internal frictional angle of the soil to be contributive to improve the results in incipient collapse phase. In the results of slope deformation analysis are close to the observation from shaking table tests before the incipient collapse. However, the soil strength discrepancy between the original and the incipient collapse phase, the results from this study are lower than shaking table tests when nailed-slopes are into the incipient collapse phase. In accordance with the critical sliding displacement concept, the shortest nails lengths for steep slopes are obtained based on the similar relationship between the reduced scale model and the prototype-scale structure (Hong et al., 2005). The optimum nail inclinations are respectively 48°, 43°, 37° and 25° for slope angle 60°, 70°, 80° and 90°. The effects of damping ratio and elastic modulus of soil mass are also considered in the study.

並列關鍵字

steep nailed slope ； earthquake ； two wedge failure mode ； Newmark method ； optimum nail inclination

參考文獻

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雙楔形滑動塊體法應用於土釘邊坡之受震分析

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