具有空間變異性之不排水長邊坡的簡化風險評估

Simplified Risk Assessment for a Spatially Variable Undrained Long Slope

李思緯(Szu-Wei Lee)

指導教授 ： 卿建業

國立臺灣大學/工學院/土木工程學研究所/博士(2019年)

https://doi.org/10.6342/NTU201903042

摘要

長邊坡的穩定性是大地工程中重要的問題，例如公路堤防、土堤、河堤及海堤等通常都具有均勻的橫切面特性，且在第三個維度中延伸一段很長的距離，而這些長土壤結構物一般都具有隨著空間變化的土壤性質。這些結構物如果產生破壞，將可能帶來重大的經濟損失及付出大量的社會成本。因此，土壤的空間變異性對於這類長『線性』結構物的穩定性問題及破壞機制的影響，是非常值得深入研究及探討的課題。
由於全球性極端氣候的影響，在一些具有特殊地形的國家或地區，堤防工程系統對他們來說是重要的國家建設工程。例如荷蘭，整個國家有四分之一以上的土地低於海平面，是世界上地勢最為低窪的國家之一，在極端氣候的影響之下，當地的國土危機將會是個非常嚴重的問題。因此，土堤的防洪系統為荷蘭的重大建設之一，而此系統被視為一個串聯系統，如破壞發生於任一區域，將可能引發災難性的後果。
為了確保這些長邊坡系統的性能合乎國家標準，使用隨機分析的結果來進行設計是必要的，例如：Vanmarcke的分析方法。然而，這個方法雖然使用上『快速』，卻存在一些確切的簡化假設，例如：有限長度的圓柱形破壞面。而這些確切簡化假設對於破壞機率估算的影響，為本論文的研究重點之一。
本論文發展一個新的簡化方法可以用來預測具有空間變異性之不排水長邊坡的破壞機率，也同時可以預測不排水長邊坡滑動塊體的長度及體積。研究發現，利用Vanmarcke的分析方法估算出來的破壞機率、滑動塊體長度及體積與一個更為嚴謹的分析方法得到的『參考解』有明顯偏差。這個新簡化方法採用一個已被修正的Vanmarcke分析方法來得到『初步解』，再使用回歸方程式校正這些『初步解』的偏差，使得最終的估算結果接近於『參考解』。
最終，本論文提出的分析方法，在不偏離Vanmarcke最初的分析方法太多的情況下，能用簡單的方式將這些估算值校正至相對『準確』的結果，這個分析流程能讓使用者作到『快速』且『準確』的簡化風險評估。

關鍵字

不排水長邊坡 ； 空間變異性 ； 可靠度 ； 風險 ； 土堤

並列摘要

The stability of a long slope is a significant issue in geotechnical engineering. For instance, highway embankments, earth embankments, river dykes and sea dykes usually have a uniform cross-section and extend for a long distance in the third dimension. These long soil structures are generally characterised by spatially varying soil properties. The failures for theses structures may have significant economic and societal consequences. Hence, the influence of soil spatial variability on the stability and failure mechanisms of these ‘linear’ structures is worthy to investigate for engineers.
The dyke engineering system is a considerable national construction project for some countries with unique topography due to the global extreme climate. For instance, more than a quarter of the country’s land is below sea level in the Netherlands. The Netherlands is one of the most low-lying countries in the world. The land crisis for this country will be a very serious problem due to the influence of extreme weather. Therefore, the earthen levee flood protection system is one of the major constructions in the Netherlands, and it can be viewed as series systems, where failure at one location can result catastrophic consequences.
In order to ensure the performance of these long-slope systems, standards explicitly require probabilistic designs. For instance, this may include Vanmarcke’s method. However, although it is ‘fast’ to evaluate, there exists some certain simplifying assumptions, e.g., the cylindrical failure surface with a finite length. The impact of these assumptions is one of the focuses in this thesis.
This thesis develops a novel method for predicting the failure probability (pf) of a spatially variable undrained long slope. The method can also predict the length (bc) and volume (Vc) of the sliding mass of the undrained long slope. It is found that the (pf, bc, Vc) solutions computed by Vanmarcke’s method deviate significantly from the reference solutions computed by a more rigorous method. The proposed novel method adopts a revised Vanmarcke’s method to obtain preliminary solutions, and regression equations are applied to correct the biases of the preliminary solutions such that the corrected solutions are close to the reference solutions. The effectiveness of the proposed novel method is demonstrated through a case study.
Finally, the proposed novel method can adopt a simple way to correct these estimations to the relatively ‘accurate’ solutuons without deviating from the original Vanmarcke’s method. The process can make users obtain ‘fast’ and ‘accurate’ simplified risk assessments.

並列關鍵字

undrained long slope ； spatial variability ； reliability ； risk ； embankment

參考文獻

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