近年來受極端氣候影響，降雨誘發之山區邊坡失穩與滑動災害日趨頻繁，本研究以嘉義縣大埔鄉台3線351K+700處公路邊坡為研究對象，整合現地調查、數值模擬與儀器監測資料，探討降雨入滲對研究區域邊坡穩定性之影響。
本研究蒐集研究區數值地形模型（DEM）、地質鑽探、地下水位、降雨紀錄及傾斜觀測管等資料，利用Groundwater Modeling System（GMS）軟體建立擬真三維地質模型及地下水位面，並匯入Fast Lagrangian Analysis of Continua in Three Dimensions（FLAC3D）數值分析軟體，模擬不同降雨條件下之未飽和土壤入滲行為。透過飽和度、安全係數、最大剪應變增量及位移分布等結果，評估降雨對邊坡穩定性之影響，並配合傾斜觀測管監測成果進行模型驗證。
依據研究區地形特徵及現地調查成果，可判釋出S-1、S-2、N及L四個潛勢塊體。數值模擬結果顯示，隨日累積降雨量逐漸增加，坡體飽和度提高且基質吸力降低，使邊坡安全係數下降。本研究依研究區最低安全係數與降雨量之關係推估，當其降至臨界值1.0時，對應之日累積降雨量約為430 mm。
滑動面分析主要針對監測資料較完整之S-1與S-2潛勢塊體進行探討，前者主要呈現淺層滑動特徵，其潛在滑動面深度約為10–15公尺；後者則具有淺層及較深層滑動型態，其潛在滑動面深度分別約為10–12公尺及20–25公尺。本研究數值模型推估之潛在滑動深度，與傾斜觀測管監測成果大致相符，顯示本研究模型具有一定合理性。
綜合研究成果顯示，降雨入滲會使邊坡穩定性降低並增加潛在滑動風險。本研究透過擬真三維地質模型，可有效瞭解降雨入滲對邊坡穩定性之影響，並將數值模擬成果作為邊坡災害評估與防治規劃之參考。

This investigation evaluates the impact of rainfall infiltration on slope stability along Provincial Highway No. 3 in Chiayi County, Taiwan. A realistic three-dimensional (3D) geological model was constructed from topographic, borehole, groundwater, and inclinometer data and imported into FLAC3D for numerical simulations.
The assessment examines four cumulative rainfall scenarios (80, 200, 350, and 500 mm) under a 24-hour uniform rainfall pattern. The numerical results reveal that higher rainfall infiltration elevates slope saturation, diminishes matric suction, and reduces the factor of safety. Based on topographic characteristics and field investigations, four potential blocks (S-1, S-2, N, and L) were identified. Notably, the factor of safety drops to the critical value (FOS = 1.0) when daily cumulative rainfall reaches approximately 430 mm.
Sliding surface analysis mainly focused on the S-1 and S-2 potential blocks due to more complete monitoring data. The former exhibits a shallow sliding surface at a depth of approximately 10–15 m, whereas the latter contains both shallow and relatively deep-seated sliding surfaces at depths of approximately 10–12 m and 20–25 m, respectively. The simulated sliding locations are consistent with inclinometer observations, demonstrating the reliability of the proposed numerical model.

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