降雨入滲影響土釘邊坡穩定性之研究

A study on the effect of rainfall infiltration on the stability of soil-nailed slopes

林湧群(Yung-Chun Lin)

指導教授 ： 馮道偉

中原大學/工學院/土木工程研究所/碩士(2004年)

https://doi.org/10.6840/cycu200400055

摘要

台灣地形多山區，人口的增加速度與建築物需求量與日具增，因此往山坡地發展是近年來反應社會經濟成長的指標。相對的，邊坡穩定性對於山坡地發展的計畫扮演了相當重要的環節，以往在分析山坡地的問題時多為採用極限平衡法，但是近三十年來有限元素法發展迅速，使坡地安全分析增加了新的方法。
本研究主要是對於邊坡的穩定性問題進行數值分析，使用的分析程式為「Plaxis」有限元素程式，此程式為多元化之大地工程問題分析程式，能以簡易的CAD方式建立工程案例幾何剖面。主要的研究項目包括：1）浸潤帶的影響；2）土釘長度與地下水位深度的影響；3）單隻土釘於邊坡上不同位置的穩定性比較；4）噴凝土對於土釘邊坡穩定的效用。
研究結果顯示：1）模擬浸潤帶土壤強度折減情況下，當強度折減至原始值的某比例時，安全係數有加速下降的趨勢，並且邊坡的潛在滑動面由深層圓弧面變成淺層破壞面；2）土釘邊坡受到地下水位的影響，在高地下水位時，土壤有效應力下降，抗剪強度相對減少，穩定性不如低地下水位。而土釘的長度在較長時，更能穩定邊坡，但是在超過邊坡穩定所需求的最小長度後，即使增加長度亦無助於安全係數之提升，因此土釘長度的設計宜考慮適合邊坡的情形；3）土釘邊坡於降雨浸潤後，能在一定的強度以上保持邊坡的穩定性，但是低於此強度後，土釘將無法發揮效用而直接在坡頂或坡趾處發生破壞；4）單支土釘於植入邊坡底部時可發揮較有效的穩定貢獻，即使降雨時仍然相同，但是邊坡潛在滑動面的位置卻由原本坡面滑動變成了延伸至坡趾外。此外，剪應變最大值的發生處也由土釘下方變成邊坡底部；5）噴凝土於土釘施工時使用，能穩定開挖的坡面，並有助於將潛在破壞面往邊坡內延伸，並些微提升安全係數。

關鍵字

土釘

並列摘要

In Taiwan, because the increasing of population and the requirement of building are getting more and more, the develop most of slope engineering has responded to the social economic growth in recent time. Therefore, the stability analysis of slopes played an important role in slope engineering, in practice the majority of slope stability analysis are still performed by using limit equilibrium method, but recently, a more powerful method of finite element method provides new way to analysis the stability of slopes.
The objective of this study is to investigate the effects of rainfall infiltration on the stability of soil-nailed slopes. The finite element problem program PLAXIS is used to perform slope stability analysis. The topics under study include : 1) the influence of wetting band; 2) the influence of nailing length and groundwater level; 3) the influence of location of single nailing ; 4) the influence of shotcrete on slope surface.
The results of this study indicate that: 1) when the soil strength in the wetting band is reduced to a certain value, the safety of slope is decreased faster and the potential failure surface changes from deep location to shallow location; 2) in high groundwater level, both the effective stress and the shear strength are decreased. Longer soil nailing can provide higher safety, but the design length should approach a minimum value; 3) with rainfall, the nailing slope is initially stable, but when the strength is reduced to a certain value, the nailing slope will failure on the upper and the toe position in the slope; 4) single nailing at lower elevation can provide higher safety factor than upper and middle elevation for rainfall condition, but the potential failure surface changes from shallow slope face to toe; 5) using shortcrete on slope surface can stabilize excavation and raise safety factor.

並列關鍵字

soil nailing

參考文獻

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