邊坡破壞機制涉及土壤力學與水文之複雜的交互作用，未飽和邊坡內部水力行為可透過土壤水分特徵曲線描述降雨入滲過程中的暫態水分變化。土壤水分特徵曲線受到孔隙結構影響具有單峰或雙峰特徵。然而，工程實務與運算簡便之考量，既有研究與分析方法多採用單峰模式進行，此類簡化往往忽略了具雙孔隙結構土壤之水文特性及水力遲滯效應，進而導致邊坡穩定性評估之偏差。
本研究整合雙峰土壤水分特徵曲線模式、參數不確定性量化以及水力遲滯效應，探討其對降雨誘發淺層邊坡破壞之綜合影響。研究首先探討單峰與雙峰模型的適用性，並分析於不同降雨條件下滲流與穩定性之差異。進一步採用貝氏更新以及馬可夫鏈蒙地卡羅法，產生隨機樣本並建置參數的不同信賴區間，以量化參數不確定性及其對穩定性之影響。最後，透過試驗數據擬合雙峰遲滯模型，探討不同水力路徑下邊坡內部之水文響應對破壞時間之影響。
研究結果顯示，雙峰模型能更精確地捕捉雙重孔隙土壤的水力特徵，對於邊坡破壞發生時程之預測較單峰模型展現出更高的適用性，且在考量不同降雨條件下得到較保守的安全係數。參數不確定性分析則揭示土壤水分特徵曲線擬合參數不僅影響水力特徵與滲流分析之結果，更是影響滑動面深度與破壞發生時程預測之關鍵。此外，受到水力遲滯效應的影響，顯著改變土壤的水分與應力分布，且不同水力路徑對安全係數的變化時序，取決於土壤材料的顆粒粗細。
綜上所述，忽略雙峰特徵、參數隨機性及遲滯效應均可能導致邊坡穩定評估之顯著誤差。本研究不僅優化了未飽和邊坡之滲流與力學分析框架，亦為工程實務中之坡地災害預警與管理提供了更為嚴謹且具科學基礎的評估依據。

Slope failure mechanisms involve complex interactions between soil mechanics and hydrology. In unsaturated slopes, internal hydraulic behavior during rainfall infiltration is characterized by transient moisture changes described by the soil water characteristic curve (SWCC). Influenced by pore structure, the SWCC can exhibit either unimodal or bimodal characteristics. However, for computational simplicity in engineering practice, existing research predominantly employs unimodal models. Such simplifications often overlook the hydrological properties and hydraulic hysteresis effects inherent in soils with dual-porosity structures, potentially leading to biased slope stability assessments.
This research integrates a bimodal SWCC model, parameter uncertainty, and hydraulic hysteresis to investigate their combined influence on the stability of rainfall-induced unsaturated slopes. First, this study evaluates the applicability of unimodal versus bimodal models, analyzing discrepancies in seepage behavior and safety factors under varying rainfall conditions. Furthermore, Bayesian updating and Markov chain Monte Carlo (MCMC) methods are utilized to generate stochastic samples and establish confidence intervals, thereby quantifying parameter uncertainty and its impact on stability. Finally, a bimodal hysteresis model is calibration using experimental data to explore the effects of hydrological responses under different hydraulic paths on the timing of slope failure.
The results demonstrate that the bimodal model more accurately captures the hydraulic characteristics of dual-porosity soils and provides superior predictive performance regarding the timing of failure compared to unimodal models, particularly showing distinct results across different rainfall scenarios. The uncertainty analysis reveals that parameter variability significantly affects seepage results and is a critical factor in predicting the slip surface depth and time to failure. Moreover, hydraulic hysteresis significantly alters the distribution of soil moisture and matric suction; the degree of conservatism in stability assessments depends heavily on the soil grain size distribution relative to the hydraulic path.
In conclusion, neglecting bimodal characteristics, parameter randomness, and hysteretic effects can lead to substantial errors in slope stability evaluation. This study optimizes the analytical framework for seepage and mechanical behavior in unsaturated slopes, providing a more rigorous and scientifically grounded basis for landslide early warning systems and disaster management in engineering practice.

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