坡面錨定系統應用於陡坡災害防治之模型試驗與分析

Model test and analysis of anchored slope-facing systems for mitigation of disasters induced by high steep slope instability

紀柏全(Po-Chuan Chi)

指導教授 ： 陳榮河

國立臺灣大學/工學院/土木工程學研究所/博士(2013年)

https://doi.org/10.6342/NTU.2013.02309

摘要

本研究探討的邊坡保護工法包括「錨定織網系統」(anchored geosynthetics/nets system)，以及「纖維加勁面層」(fiber-reinforced facing)，兩者之優點在於可同時提高邊坡淺層及深層之穩定性。其中錨定織網系統係以錨釘配合地工織物，將錨釘穿過織物並貫入坡體內，使織物產生張力，此張力可對表面土壤產生圍束力；同時，地工織物可抵抗雨水或地表水沖蝕。此外，纖維加勁面層係將連續纖維(continuous filaments) 與砂土同時噴射於裸露坡面，此加勁面層除可抵抗表面沖蝕，並可作為植生基材，同時形成一柔性擋土結構，亦可依現地條件配合錨釘提高邊坡穩定。本研究以砂箱模型試驗，配合邊坡極限平衡分析以及數值分析，獲知錨定坡面系統之加勁力學機制與破壞模式，並透過影響因子之探討，提供應用之參考。
針對錨定織網系統，首先透過縮小1/10尺寸之模型邊坡試驗，觀察錨定織網加勁系統應用於陡坡之行為；試驗過程藉由質點影像測速儀 (Particle Image Velocimetry, PIV) 分析顆粒的運動。結果顯示，以鋼線施加錨定力於坡面之邊坡中，乾坡之破壞類似楔型塊體破壞；受滲流作用時，則呈現弧形滑動。以土釘錨定坡面，滑動區域亦似弧形塊體移動。另外，坡面加勁材發揮良好阻留 (retention) 以及排水功效，在破壞發生前後皆能防止土壤流失，並可快速將水排出，而避免更大規模破壞。
極限平衡分析獲得之滑動面位置與安全係數與模型試驗結果相當吻合，證明極限平衡分析可作為錨定織網系統穩定分析之用。另由數值分析結果顯示，因所需錨定力較低，緩坡產生位移時，織物須發揮較大張力，方能穩定淺層土壤。而以土釘錨定之邊坡，因土釘承受大部分土壓力，因此織物之張力發揮較小。此外，若滲流方向與土釘打設方向垂直，則加勁功效較佳；另外，增加土釘長度亦可減少塑性區之發展。
纖維加勁面層之砂箱模型試驗，發現面層加入纖維可有效降低牆面變形及坡頂沉陷量。在相同荷重作用下，面層水平位移量及沉陷量隨著坡面變陡而增加。此外，重力式擋土牆型式在高荷重下可發揮較佳之保護功效。極限平衡分析顯示，安全係數隨面層厚度增加而提高，但具有一最佳值，且陡坡之最佳值低於緩坡。數值分析結果發現，不含纖維面層之強度及勁度皆較小，無法如纖維加勁面層可承受額外作用力，加載之應力大部分由土釘承受。此外，施工時應先施作面層後打設土釘可有效降低坡面位移。

關鍵字

陡坡 ； 錨定 ； 地工織物 ； 模型試驗 ； 穩定分析 ； 數值分析

並列摘要

Two reinforced systems were researched and discussed in this study: the anchored geosynthetics/nets system and the fiber-reinforced facing. Both of the systems may combine anchor pins, nails, natural or synthetic geotextiles, thereby effectively increasing the stability of the slope face and preventing deep slides from occuring.
For anchored geosynthetics/nets system, a series of model tests on steep slopes formed by sandy soil were conducted to investigate the mechanism and failure behavior of the reinforced slopes with anchored facing system. The particle image velocimetry (PIV) technique was used to measure the displacement of soil particles during the moving process. The test results showed that application of a geotextile contributed to effectively retain soil particles, prevent accumulation of water pressure in the slope, and restrain the run-out distance when the slope failed. With regard to the failure mode, dry slopes anchored with stainless wires behaved as a wedge sliding, while a circular failure mode was observed in slopes subjected to seepage. On the other hand, the failure of the slope reinforced with nails was similar to a coherent block sliding.
The limit equilibrium analysis indicates that the analysis can be applied to analyze the stability of the AGS system. Moreover, the result of numerical analysis shows that higher tensile force is developed in the geosynthetic facing on gentler slope.
For the fiber-reinforced facing system, a number of model slopes of two types of structure, gravity and facing types, with various facing angles were performed. The test results verified the effectiveness of the reinforcement in restraining the deformation of the slope. Moreover, the gravity-type displayed significant effectiveness to decrease the lateral deformation of the facing even under high surcharges.
The result of limit equilibrium analysis shows that the fiber-reinoforced facing is capable to resist high overburden pressure. From numerical analysis, it is found that the nails in the steeper slope tended to be pullout due to the tendency of overturning of the slope. The the fiber-reinoforced facing system was analyzed through parametric study of a full-scale slope, and it was confirmed to act as an effecive protection method to the slope.

並列關鍵字

steep slope ； anchoring ； geotextiles ； model test ； limit equilibrium analysis ； numerical analysis

參考文獻

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