Model tests for development process of slope failures due to extremely heavy rain

[[abstract]]本研究以沉泥質砂土在三種不同尺寸的流槽中進行實驗，分別為長1.75 m、寬1.35 m、高0.7 m，土層厚度0.28 m、長1.94 m、寬0.645 m、高0.7 m，土層厚度0.38 m及長2.29 m、寬0.645 m、高0.84 m，土層厚度0.42 m，堆置一坡角為30°的邊坡，並進行模擬降雨試驗，探討邊坡在豪雨中的破壞機制、土砂流出特性及土層厚度改變所造成之影響。於邊坡的坡趾、坡中與坡頂埋設有土壤水份計和孔隙水壓計，用以監測降雨時邊坡內部含水量與孔隙水壓變化，並藉由邊坡模型匯流口所收集邊坡破壞後所排出雨水及土砂之混合物，來觀察其排放率與混合物體積濃度變化情形。 研究結果發現，邊坡中段底部與邊坡坡趾底部的土壤水份計曲線到達峰值時的時間點之差值可參考做為關鍵避難時間，此關鍵避難時間值隨著降雨強度增強而縮短。邊坡中土壤水份計有兩種反應曲線，第一種為直線上升型，第二種為兩階段上升型。第二種反應曲線較容易發生於降雨強度低且土層較厚之中間部位。由砂土排放歷線之發動期觀察得知，降雨強度對於邊坡破壞發動時機的影響為負相關但非線性。[[abstract]]A series of artificial rainfall tests were performed on three sizes were 0.28 m, 0.38 m, 0.42 m thick sandy slopes with a slope angle of 30°. Wooden sand boxes with 1.75 m long, 1.35 m wide and 0.7 m high, 1.94 m long, 0.645 m wide and 0.7 m high, and 2.29 m long, 0.645 m wide and 0.84 m high were used with soil moisture sensors and a data acquisition system to monitor the interior soil moisture response to the rainfall infiltration. The present study features the measurement of solid and water discharge from the slope subjected to rainfall. This substantiates the investigation into the relationship between the soil moisture response and the solid discharge (or waste) process. Experimental evidences revealed that the time difference of slope middle and slope toe moisture response curve’s peak value able to be critical refuge time, that time decrease attach to rainfall intensity increase. There were two kinds response curve of moisture sensor, first is direct rising, second is two steps rising. The second kind response curve usually appear at small rainfall intensity and middle of slope. Observed the starting period of soil discharge curve revealed the negative relationship between rainfall intensity and critical slope failure time but nonlinear.[[note]]碩