降雨引致邊坡地下水位變動及作為邊坡崩壞預警指標之研究

Investigating the Rainfall-Groundwater Relationship as an Early Warning Index of Slope Stability

曾致仁(Zhi-Ren Tseng) ； 李德河(Der-Her Lee) ； 吳建宏(Jian-Hong Wu) ； 林宏明(Hung-Ming Lin)

《中華防災學刊》 10卷1期 (2018/02) Pp. 17-29

摘要

為探討南部山區常見崩積層、砂頁岩互層以及板岩區之邊坡滑動機制與地下水位變動關聯性，本研究於阿里山公路、南橫公路以及藤枝林道選定試驗場址進行鑽探樣本的室內試驗求得邊坡材料之力學強度參數與現地監測取得地層變動資料。利用Tank model探討降雨量與地下水位變動之關係，再以數值軟體Geo-Studio中之seep/w模組以及slope/w模組進行模擬地下水位上升對邊坡安全性的影響。經由筒狀模式計算後，降雨量與地下水位變化量存在關係式為Δh=β×α×(R-R_T)，且根據模擬邊坡滑動臨界值(FS=1)所得之臨界地下水位上升量可逆推出臨界累積降雨量，在台18線試驗邊坡當累積降雨量達1149.73mm時，淺層滑動面達到臨界狀態；累積雨量達到1,352.28mm時深層滑動面則有深層崩壞的可能。在台20線試驗邊坡，當累積降雨量達到1169.15mm時，淺層地表下7m處滑動面有滑動的可能；累積雨量達到1,363.19mm時，地表下20m之滑動面則可能達到臨界狀態。在藤枝林道12k試驗邊坡，當累積降雨量達到3,501.50mm時，淺層滑動面可能產生滑動；當累積降雨量達到3,816.10mm，則有大規模崩壞的可能。本研究成果初步針對三處不同地質之邊坡提出預警警戒值，未來將持續監測以建立更準確之預警指標。

關鍵字

邊坡穩定 ； 筒狀模式 ； 降雨與地下水位變動 ； 邊坡預警

並列摘要

This study investigates three sites at Alishan Highway 86K+950, South Cross-Island Highway 52K+150, Tengchi Forest-road 12K to correlate the sliding mechanism and the groundwater fluctuation at the colluvium, sandstone and shale interlayer, and slate, respectively, in the mountainous areas in south Taiwan. Firstly, literature review, laboratory tests to obtain physical and mechanical properties of the local geological rocks/sands, and in-situ monitoring are conducted. Then, the relationship between rainfall and groundwater fluctuation is discussed using Tank Model. The impact of the groundwater level to the slope stability is simulated by commercial numerical software, Geo-Studio. The computational results of Tank Model show a linear relationship between rainfall and groundwater level as Δh=β×α×(R-R_T). Critical cumulative rainfall can be derived by the critical groundwater level from slope simulation with FS=1. In the Alishan Highway site, a shallow slope failure occurs when the cumulative rainfall reaches 1149.73mm; while the deep sliding surface reaches to the critical state when the cumulative rainfall comes to 1352.28mm. In the South Cross-Island Highway site, the sliding surface at the depth of 7m moves when the cumulative rainfall reaches 1169.15mm. The sliding surface at 20m below the surface reaches the critical state when the cumulative rainfall reaches 1363.19mm. In the Tengzhi Forest-road slope, the shallow sliding surface may move when the cumulative rainfall reaches 3501.50mm. There will be the possibility of large-scale landslide when the cumulative rainfall reaches 3816.10mm. The results of this study are the preliminary early warning index to the slopes with three different geological conditions. The monitoring will continue to increase the accuracy of the warning indicators.

並列關鍵字

Slope stability ； Tank model ； Rainfall and groundwater level fluctuation ； Slope early warning