植生及降雨對邊坡穩定影響之模式分析

Abstract

植生的應用乃為生態工程當中不可或缺的重要元素，然而在邊坡穩定上植生之施工為必然之趨勢，其根系對於邊坡穩定之效益在以往許多學者的研究中可以有相當程度上的了解。但大體來說，植生對於邊坡穩定之影響不完全侷限於根系力學上，尚有許多不同的影響因子，例如：樹重、風載力、降雨截流以及入滲變化等。這些都會影響植生在邊坡穩定上的結果。 本文乃利用模式分析去探討在不同坡度及水文條件下，植生的存在對於邊坡穩定上實際的效果。在根系力學的模式當中，本研究利用吳正雄（1990）'植生根力與坡面穩定關係之研究'中，其對台灣杉及山黃麻的根系力學所做的分析結果作為基礎，再利用Slope/W（Geo-Slope,1991）地層及破壞面上的資料，最後經由8種不同水文條件下的Bishop修正分析法及Janbu簡化分析法去分析破壞面上無植生及不同植生方式下坡面的安全係數值。 分析結果發現，台灣杉及山黃麻於破壞面最深深度1.3ｍ之破壞面分別可提升安全係數0.88至1及0.77至0.93；於破壞面最深深度3.4ｍ之破壞面，台灣杉及山黃麻分別可提升安全係數0.05至0.13及0.04至0.12；於破壞面最深深度4.9ｍ之破壞面，台灣杉與山黃麻之安全係數變化皆於-0.01至0.05之間；然而於更深之破壞面上植生所能增加之安全係數皆於0.03以下，於乾燥狀態下甚至使得安全係數降低0.017，顯示破壞面較深則植生對安全係數之效益將毫無作用，甚至會讓安全係數降低。 最後，植生並非完全適用於每個邊坡的生態工程設計上，必須經由更細密的研究分析，才能夠找出真正適用於特定邊坡上的生態工程。

Planting is an indispensable element of ecological engineering. It is the ultimate option for slope stabilization. Past researches have shed light on the effect of the roots in steadying gradients. This paper employs pattern analysis to explore the impact of planting on slope stabilization under different grades and hydrological conditions. The mechanical model of the root system in this study is based on Mr. Wu Jheng-Syong’s “Relations of Root System Mechanics and Slope Stability” (1990) in which he studies root system mechanics of Taiwania and India-charcoal trema. Geological layer and destruction surface data of Slope/W（Geo-Slope,1991）are then utilized. Finally through Bishop’s adjusted analysis method and Janbu’s simplified analysis method under 8 different hydrological conditions, slope safety coefficients of destruction surface without plant or with plants of different kinds. Analysis outcomes indicate Taiwania and India-charcoal trema are capable of raising safety coefficients of destruction surface at 1.3m under from 0.88 to 1 and from 0.7 to o.93 respectively. At the destruction surface at 3.4m under Taiwania and India-charcoal trema are capable of raising safety coefficients from 0.05 to 0.13 and from 0.04 to 0.12 respectively. At the destruction surface at 4.9m under, changes in safety coefficients caused by Taiwania and India-charcoal trema are both between -0.01 and 0.05. At deeper destruction surface increases in safety coefficient caused by planting are all below 0.03. Under dehydrated conditions, the safety coefficient is lowered by 0.017, indicating the fact that at deeper destruction surface planting does not enhance the safety coefficient and may cause it to decrease. Finally planting may not be appropriate for ecological engineering of every slope. Detailed study and analysis are required for identifying the suitable ecological engineering for a particular slope.