台灣的山坡地面積占全區70%以上，除了地震外再加上颱風、豪雨等侵襲，造成崩塌事件頻繁發生，其中又以大規模崩塌造成更嚴重之災害，民國98年由莫拉克颱風所引發的小林村大規模崩塌，更是引起許多國人的注意。因此對於大規模崩塌之災害潛勢，以及影響範圍的掌握度就成了重要的研究課題。
本研究主要目的為建立大規模崩塌穩定性分析與影響範圍評估的分析流程，並藉由蘭台案例驗證該分析流程計算之影響範圍的合理性。首先透過各時期之航空照片及數值地形推測過去崩塌可能發生的位置，接著由鑽孔取樣成果來研判地層及斷層之相關位置，並進行數值模型的建立，結合前人材料試驗及地下水位監測之成果，模擬崩塌區可能之滑動面，最後選擇符合地表特徵且安全係數最低的滑動面，分析滑動發生時該滑動面之流動長度及面積。
研究方法包含使用地理資訊軟體整理數值地形、三維極限平衡法進行邊坡穩定性分析並決定崩塌範圍、最後用影響範圍分析軟體LS-RAPID分析滑動長度及面積。本研究以宜蘭縣太平山蘭台苗圃地區，宜專一線13.5公里處邊坡進行案例分析。
研究成果發現潛在大規模崩塌之滑動面，在高水位時之安全係數非常接近1。滑動時大部分的量體會停留在滑動面上，只有少部分量體會流入河谷中。
本研究之案例中，地下水位、材料強度異向性、支撐強度、切片大小等參數對滑動面之形狀、最大深度、面積、與體積的影響並無明顯規律；而針對特定滑動面時，地下水位及強度異向性參數對安全係數的變化趨近線性關係，而無效擋土設施及足夠細的切片大小則不影響安全係數。
本研究亦將LS-RAPID求得的滑動長度與水保局定義崩塌類型為重力堆積型的滑動距離進行比較，將Slide計算之崩塌面積用水保局之經驗公式轉換後，得出之公式解與LS-RAPID之計算成果差異不大，因此LS-RAPID可以做為重力堆積型崩塌之影響範圍評估的工具。

Slope land in Taiwan account for more than 70% of the entire region. In addition to earthquakes, typhoons and heavy rains have caused frequent occurrences of landslides. The large-scale landslide of Xiaolin Village during Typhoon Morakot in 2009 caused severe damage and attracted the attention to many people. Therefore, the potential of large-scale landslide and its affected area have become an important research topic.
The main purpose of this research is to establish an analysis process for the stability analysis and the affected area of large-scale landslides. The procedure is then verified by inspecting whether the affected area calculated by this analysis process is reasonable through the Lantai case study. In-situ conditions are gathered through aerial photos, satellite images, and core sampling. They are then used to interpret the possible locations of landslides and the positions and orientations of strata and faults. A numerical model, combined with the results of previous material tests and groundwater monitoring, is then established. The model yields possible sliding surfaces in the landslide area. The sliding surface that meets the characteristics of the observed landslide and has the lowest safety factor is then selected to further analyze its sliding length and affected area.
This research uses QGIS, a geographic information system, to sort out the numerical terrain. Slide3 is then used to analyze the stability of the slope with limit equilibrium concept. LS-RAPID then takes the output from Slide3 with additional inputs to evaluate the sliding length and affected area. This study uses Lantai area a case study.
The results suggested in the studied case the safety factor at high water level is very close to 1 and fails to meet the slope engineering design standards. During sliding, most of the masses will stay on the sliding surface, and only a small part of them will flow into the valley.
In the case studied, groundwater level, material strength anisotropy, support strength, and slice size in Slide3 has negligible influence on the shape, maximum depth, area, and volume of the sliding surface. If one is interested in a specific sliding surface, its safety factor varies linearly with the groundwater level and strength anisotropy parameters. Finally, inner retaining facilities and slice size do not affect the safety factor.
The sliding distance predicted using LS-RAPID is compared with an empirical relationship to verify its performance. First, the landslide area predicted by Slide3 is converted into sliding volume using empirical equation developed by the Soil and Water Conservation Bureau for gravity accumulation type debris flow. The volume is then used in Scheidegger’s empirical equation to obtain the sliding length. This length is very similar to the sliding distance predicted using LS-RAPID. Therefore, LS-RAPID can be used as a tool for evaluating the affected area of gravity accumulation type debris flow.

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