震後山崩降雨警戒值變化之研究

A study on change of rainfall triggering slope failure due to earthquake

盧之偉(Chih-Wei Lu)；林子聖(Tzu-Sheng Lin)；李威霖(Wei-Lin Lee)；林郁峰(Yu-Feng Lin)；蔡元融(Yuan-Jung Tsai)

大規模崩塌 ； 地震 ； 邊坡穩定 ； 雨量警戒值 ； Landslide ； Earthquake ； Slope stability ； Rainfall warning thresholds

中華防災學刊

16卷2期（2024 / 09 / 01）

139 - 148

繁體中文;英文

臺灣處於環太平洋地震帶和颱風路徑交會處，地質水文環境獨特，易發生山崩、地滑和土石流等災害。因此臺灣在防災上實施高標準的防治措施，並搭配軟體因應對策，其中又以促崩降雨警戒值扮演關鍵資訊。此外，地震對邊坡穩定性產生影響，使邊坡內部變形及強度降低，故震後促崩降雨警戒值的設定應低於震前。然而，現行調整方式主要基於歷史災害事件和經驗，缺乏以物理模型為基礎的方案，往往會造成進退失據。本研究嘗試運用有效應力數值分析技術，搭配高階的土壤模型，針對不同坡度和土壤性質，分析不同地震規模下邊坡內部強度的變化，用以建立適應不同情境的降雨警戒值調整機制。研究顯示，以中等緊密砂土組成的邊坡受震後強度下降最多，建議調降警戒值20%以上；中等緊密砂土組成的邊坡強度回復時間最長，可能需半年以上。

Taiwan is located in the seismic zone of the Pacific Ring of Fire and typhoon pathways, so that its geological and hydrological environment unique and prone to disasters such as landslides, mudslides, and debris flows are very frequent. Consequently, Taiwan has implemented high-standard disaster prevention and control measures, complemented by software-based strategies. Among these, the rainfall-triggered landslide warning threshold plays a crucial role. Moreover, earthquakes have a significant impact on slope stability, leading to internal deformation and reduced strength. Therefore, the post-earthquake rainfall warning threshold should be set lower than that before the earthquake. The current adjustment method relies mainly on historical disaster events and empirical data, lacking a physically-based model. In this study, the numerical analysis is utilized to analyze variations in internal slope strength under different seismic scales for various slope gradients and soil properties. The aim is to establish an adaptive mechanism for adjusting rainfall warning thresholds under different scenarios. The research indicates that slopes composed of medium dense sandy soil exhibit the most significant strength reduction post-earthquake, suggesting a recommended adjustment of the warning threshold by more than 20% and potentially requiring more than six months to recover the strength.