非飽和土壤邊坡於人工降雨下暫態孔隙水壓力分佈之數值分析

Numerical modeling of transient pore-water pressure distribution of an unsaturated soil slope under rainfall infiltration condition

吳家賢(Chia-Hsien Wu 吳家賢)

指導教授 ： 魏敏樺

國立臺北科技大學/工程學院/土木與防災研究所/碩士(2011年)

https://doi.org/10.6841/NTUT.2011.00252

摘要

台灣屬於四面環海，高山林立之島嶼國家，面臨著土地狹小、蓄水不易與山林地邊坡土石流之困擾，因此邊坡破壞課題非常重要，每當雨季或颱風降雨豐沛時期往往造成地下水位急速升高或濕潤介面(wetting front)達到非飽和土壤區導致邊坡產生滑動面進而發生土石流或邊坡沖刷破壞。
本研究先以FlexPDE數值分析軟體模擬汙染傳播之虛擬案例，進而驗證此數值軟體的可靠性，接著模擬前人提出長2.5 m、寬1 m、高1.44 m之人工降雨模型邊坡實驗，比對實驗數據（含水量與孔隙水壓）與數值分析模擬值，並探討不同土水特性曲線與非飽和滲透係數的異向性對降雨邊坡之影響，最後以擬真邊坡探討設置不同排水孔對邊坡內部孔隙水壓消散與邊坡穩定性。模擬結果顯示濕潤介面首先入滲至不透水層，由於水無法再繼續入滲或排出導致水從不透水層往上累積，造成坡址開始產生掏刷引起後退式的淺層崩壞。初步模擬結果也顯示在邊坡坡面設置多排水孔能有效預防降雨邊坡中之孔隙水壓累積與邊坡水平位移。

關鍵字

非飽和土壤；邊坡 ； 降雨入滲；基質吸力；FlexPDE；孔隙水壓

並列摘要

The abundant rainfalls brought by typhoons and during prolonged rainy season have often resulted in the rapid rising of water table, which was presumably due to the infiltration and propagation of wetting front from the surface of the slope and through the unsaturated soil zone above the water table. As a result, shallow landslides have often been encountered during or after these prolonged rainfall periods. Therefore, to mitigate landslide problems, it is important to understand the mechanism of water infiltration and propagation of wetting front.
In this study, the partial differential equations involved in the transient flow of water in unsaturated soil medium have been solved using a numerical tool. The reliability of the numerical tool had been calibrated against published pollutant problems. The study then modeled a case history where a 2.5 m long by 1 m wide by 1.44 m high model slope was subjected to artificial rainfall. The numerical result was compared to the experimental data in terms of water content and pore-water pressure. The effects of different soil-water characteristic curves and anisotropic hydraulic conductivity on the patterns of wetting front were then examined. The patterns of pore-water pressure distribution in finite and infinite slopes were also compared.

並列關鍵字

unsaturated soil；slope ； rainfall-infiltration；matricsuction；FlexPDE；pore water pressure

參考文獻

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