探討降雨強度趨勢與重現週期對未飽和邊坡穩定之影響

Effect of Variations in Rainfall Intensity and Different Return Period Rainfall Events on Unsaturated Slope Stability

蔡易縉(Yi-Jin Tsai) ； 葉信富(Hsin-Fu Yeh)

《農業工程學報》 65卷2期 (2019/06) Pp. 34-50

https://doi.org/10.29974/JTAE.201906_65(2).0004

摘要

降雨型態做為邊坡安全的考量因素受到氣候變遷之影響而發生改變，本研究藉由趨勢分析以及頻率分析等水文統計方法，探討曾文水庫集水區的降雨強度變動以及不同重現週期之降雨量變化，藉此瞭解未來邊坡可能面臨之降雨情境。另外，研究中以水文分析之結果設計降雨案例，並使用水力耦合模式進行邊坡穩定性分析，討論降雨型態變遷對邊坡之影響。趨勢檢定結果顯示，曾文水庫集水區之降雨強度呈現增加之趨勢，且最大一日降雨強度變化最為明顯，每年約增加0.08毫米／小時。邊坡穩定分析結果則顯示，在2016年、2050年及2100年降雨案例中，斜坡深度2.5公尺處土壤安全係數分別下降了4.8%、8.1%及12.2%，代表未來邊坡深處土壤穩定性將各易受降雨影響而降低。透過頻率分析及邊坡穩定性分析，可知重現期越長之降雨，其降雨強度較高，因此降雨入滲行為快速。研究中由斜坡處3.0公尺深之土壤安全係數變動，可見在3日降雨期間，土壤安全係數並未受2年重現期降雨所影響，而10年及100年重現期之降雨則使土壤安全係數分別在48小時與32小時發生明顯下降現象。而根據2016年臺灣氣候變遷推估與資訊平台計畫之調查報告，可知未來發生極端強降雨機率提高，因此未來若能取得邊坡現地資料進行此類降雨情境分析，將能提前預防邊坡災害發生或減小其危害。

關鍵字

降雨型態 ； 趨勢分析 ； 頻率分析 ； 水力耦合模式 ； 邊坡穩定

並列摘要

Rainfall patterns considered a factor in slope stability, are affected by climate change. This study conducts a trend analysis and a rainfall frequency analysis to examine rainfall intensity variations and rainfall amount for various return periods in order to understand the rainfall pattern changes in the Zengwen reservoir catchment area in the future. Then, a coupled hydromechanical framework is used to analyze the effect of rainfall pattern changes on slope stability. The results of the trend analysis reveal an increasing trend from 1990 to 2016. The trend (slope) of the one-day rainfall events is the largest, with an average slope of 0.08 mm/h per year. The slope stability analysis results reveal that if the rainfall intensity continues to rise in the future, precipitation will more easily infiltrate the soil, decreasing stability. For rainfall in 2016, 2050, and 2100, the LFS (Local Factor of Safety) of soil at a slope depth of 2.5 m decreased by 4.8%, 8.1%, and 12.2%, respectively. Moreover, the results of the frequency analysis show that rainfall intensity, and thus the infiltration rate, increased with increasing return period. For rainfall events for a 2-year return period, the LFS of soil at a slope depth of 3.0 m did not show an obvious drop. However, for 10- and 100-year return periods, the stability of soil started to decrease at 48 h and 32 h, respectively. According to a Taiwan Climate Change Projection and Information Platform) report (2016), there is an increase in the probability of extreme rainfall events in the future. The slope data (e.g., slope topography, slope structure, and soil mechanical and hydraulic parameters) obtained from the field in this study can be used to prevent or reduce the hazards of slope disasters.

並列關鍵字

Rainfall pattern ； Trend analysis ； Frequency analysis ； Coupled hydromechanical framework ； Slope stability