傳統用於預測淺層邊坡破壞的降雨強度–延時（I–D）閾值多為經驗統計方法建立，且缺乏與坡體內部水文過程之明確連結，因此在不同降雨條件下的可靠性仍受到限制。本研究透過整合臨界吸應力–深度剖面與基於極限平衡分析及統一有效應力理論所推導之降雨強度–延時閾值曲線，建立一套具物理基礎的邊坡破壞預警架構。該方法僅需降雨資料作為輸入，不依賴即時地下監測設備，因此在監測資料不足之地區亦具有良好的應用潛力。
為考慮前期降雨對坡體入滲狀態之影響，本研究引入前期降雨延時估算方法，使坡體初始入滲條件能以具物理意義的方式加以描述。透過耦合之暫態入滲–穩定性模擬結果顯示，控制邊坡破壞啟動的主要因素為降雨入滲量，而非總降雨量。不同降雨時間分布會產生顯著不同的入滲反應；當降雨強度集中於事件前期時，入滲效率較高且更易提早誘發坡體失穩；相反地，當降雨強度峰值出現在降雨後期時，坡體表層較易形成飽和區並產生地表逕流，限制雨水入滲並延遲破壞發生時間。基於上述結果，本研究提出在相似條件下，以造成最早破壞時間之降雨分布型態作為預警判定之保守依據。此外，本研究亦分析降雨紀錄不完整情境下之預測表現，結果顯示預測能力與降雨資料更新間隔、歷史資料完整度以及前期降雨條件設定密切相關。即使在部分資料缺失的情況下，系統仍能於破壞發生前提供可靠之預警訊號。最後，本研究將降雨閾值曲線建立方法延伸至多土層邊坡情境，探討土層滲透性配置與層間破壞機制對降雨閾值曲線分布之影響。
整體而言，本研究成果為降雨誘發邊坡破壞預測提供一套具物理意義且具實務操作可行性的預警基礎，並進一步說明土層分布與破壞機制在降雨閾值建立與預警系統應用中的關鍵角色。

Traditional rainfall intensity–duration (I–D) thresholds used to predict shallow slope failures are primarily derived from empirical statistical methods and lack explicit linkage to internal hydrological processes within slopes; therefore, their reliability remains limited under varying rainfall conditions. This study establishes a physically based slope failure early warning framework by integrating the critical suction stress–depth profile with rainfall intensity–duration (I–D) threshold curves derived from limit equilibrium analysis and unified effective stress theory. This method requires only rainfall data as input and does not rely on real-time subsurface monitoring, thereby offering strong applicability in data-scarce regions.

To account for the influence of antecedent rainfall on the infiltration state of the slope, this study introduces an antecedent rainfall duration estimation method, enabling the initial infiltration state of the slope to be characterized in a physically meaningful manner. Coupled transient infiltration–stability simulations indicate that the primary factor controlling the initiation of slope failure is infiltration amount, rather than total rainfall. Different rainfall temporal patterns result in significantly different infiltration responses. When rainfall intensity is concentrated in the early stage of an event, infiltration efficiency is higher, leading to earlier initiation of slope instability. Conversely, when peak rainfall occurs during the later stage, a near-surface saturated zone is more likely to develop, promoting surface runoff, limiting infiltration, and consequently delaying the onset of slope failure. Based on the above findings, this study proposes that, under similar conditions, the rainfall temporal pattern that results in the earliest failure time should be adopted as a conservative criterion for early warning. Furthermore, the predictive performance under incomplete rainfall records is evaluated. The results indicate that prediction capability is closely related to the rainfall data update interval, the completeness of historical records, and the specification of antecedent rainfall conditions. Even in the presence of partial data gaps, the system is still capable of providing reliable warning signals prior to failure. Finally, this study extends the rainfall threshold framework to multilayered slope conditions, investigating the effects of soil permeability configuration and interlayer failure mechanisms on the distribution of rainfall threshold curves.

Overall, the findings provide a physically meaningful and practically applicable basis for predicting rainfall-induced slope failure, and highlight the critical roles of soil stratification and failure mechanisms in the development of rainfall thresholds and early warning applications.

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