降雨誘發水庫集水區邊坡崩塌模式與整治策略之研發---總計畫暨子計畫：水庫集水區邊坡非飽和表層土壤之現場試驗與監測(I)

Abstract

水庫集水區邊坡崩塌、沖蝕與土砂之運移，在水庫內淤積，已嚴重威脅國內水庫蓄 水功能以及使用之壽命。國內水庫集水區發生崩塌之邊坡大多被崩積土壤所覆蓋，由於 在地下水位以上，處於非飽和狀態，受負孔戲水壓的影響，維持邊坡的穩定。許多崩塌 乃是受長期或暴雨影響使得土壤因飽和而失去負孔戲水壓，進而產生崩塌。本研究將專 注於集水區邊坡受降雨而引發崩塌之機制與其整治為主，進行研究。本計畫之總體目標 是藉由現場觀察/試驗與室內之試驗與分析，從地質與非飽和土壤力學的觀點來確立台灣 典型水庫集水區邊坡崩塌之機制、降雨事件對水庫輸砂量產生的衝擊與建立邊坡崩塌整 治策略。本計畫之分析架構根據，Iverson 模式考慮非飽和土壤之滲流，其強度隨基質吸 力之變化，以及發展使用非擾動試體以及現地試驗的方法來決定這些參數的方法。使 用此一分析架構配合降雨模式，估算集水區受降雨影響而產生之土砂量。研究中將選擇 兩處試驗基地，進行非飽和土壤取樣，現地試驗以及邊坡穩定監測研究。結合降雨型態 之分析，本整合型計畫期望就降雨、土壤特性與水庫集水區崩塌地穩定間關係與整治方 法提出建議。

The collapse and erosion of earth slopes in reservoir watersheds result in transport of silt and eventual sedimentation in the reservoir. The accumulation of sediment has seriously threatened the functionality and longevity of our reservoirs. The potentially unstable slopes in the reservoir watersheds are often covered by colluvial soils and above the water table. The colluvial soils are usually in an unsaturated state. The unsaturated soil slope maintained its stability as a result of negative pore pressure existed in the ground. The collapse of earth slope occurs often due to infiltration and saturation of the surficial soils after heavy rainfall. This research project concentrates on the mechanisms of the earth slope failures and their mitigation. Two research sites will be selected where a series of field observation/experiment, sampling and laboratory tests will be conducted to accomplish the goals of the research. Analysis will be performed from unsaturated soil mechanics point of view. Correlations among geology, infiltration, and loss of strength will be established for typical reservoir watershed in Taiwan. A framework under the Iverson model will be created where the loss of unsaturated soil strength through infiltration as a result of rainfall can be readily computed. With this framework and a rainfall model, the quantity of sedimentation load can be estimated and policies regarding the mitigation of earth slopes in reservoir watersheds will be suggested.