降雨誘發松茂地滑區淺層坡地崩塌之研究

Analysis of Rainfall-Triggered Shallow Landslides in Songmao Region

葉信富(Hsin-Fu Yeh) ； 鄭佳元(Chia-Yuen Cheng) ； 李振誥(Cheng-Haw Lee)

《中華水土保持學報》 41卷2期 (2010/06) Pp. 113-142

https://doi.org/10.29417/JCSWC.201006_41(2).0007

摘要

本研究主要利用二維有限元素滲流法模擬未飽和層中之降雨入滲行爲，邊坡穩定分析中結合滲流理論，探討降雨入滲在未飽和淺層邊坡中孔隙水壓之改變對坡地穩定的影響，本研究利用數值分析軟體Geo-Studio模擬雨水入滲至未飽和邊坡之行爲，以SEEP/W進行邊坡滲流分析，將所得之壓力水頭資料輸入邊坡穩定分析軟體SLOPE/W求得各時間段安全係數之變化，進而探求降雨入滲造成淺層邊坡滑動之機制。
本研究主要分爲兩部份，首先進行均質邊坡穩定影響因子敏感度分析，包含邊坡幾何、土壤材料性質及降雨強度。結果顯示隨著坡角、坡高及降雨強度增加易造成邊坡不穩定，而土壤材料性質與降雨強度爲最重要決定因子，其決定坡地因降雨產生的入滲條件，進而造成土壤中孔隙水壓的變化情況。另外，本研究以台中縣松茂地滑區爲研究區域，以現地實際降雨事件進行模擬，結合現場鑽探資料比對驗證松茂地滑區之滑動機制。由降雨事件模擬結果顯示，松茂地滑區遭逢降雨時邊坡淺層土壤孔隙水壓力變化顯著，且當雨水入滲至約2m時，邊坡安全係數有明顯下降至臨界值1.0之趨勢，並由現地傾度管監測資料顯示有明顯位移現象，因此本研究以數值模擬之結果是符合松茂地滑區之滑動機制，可以作爲未來對於松茂地滑區坡地穩定研究之參考。

關鍵字

未飽和層 ； 入滲 ； 孔隙水壓力 ； 邊坡穩定

並列摘要

The purpose of this paper is to use the finite element computer program SEEP/W to simulate the changes of pore water pressure when the slope is subjected to different rainfall event. The pore water pressure distribution computed in the program SEEP/W is imported into SLOPE/W for the slope stability analysis. The time-dependent pore water pressure distribution could therefore be used to compute the factor of safety with time directly.
This study is divided into two parts, the first part is to process sensitivity analysis of controlling parameters, including general geometry, soil property and rainfall intensity. From this result, it indicates soil property and rainfall intensity are the most important factors to influence the slope stability. In the second part, the Songmao region in Taichung which has been examined by modeling local rainfall events and coupled with the monitored data from field to determine the slope stability mechanism. By the rainfall events, the simulation indicated safety factor of slope decreased by less than 1.0 when the rainfall infiltrates at 2.0m depth and the monitored data also revealed displacement in the evidence. In conclusion, the slope failures have been attributed to the increase of pore water pressure and decrease of shear strength when rainfall occurs.

並列關鍵字

unsaturated zone ； infiltration ； pore water pressure ； slope stability