台2線 68K 八斗子滾石災害致災成因初探

基隆市北寧路於2013 年8 月31 日下午發生高強度降雨事件 (最高達94.5 mm/hr)，並導致台2 線68K+000 處於當日16 時19 分左右發生落石擊毀小客車之意外。本次落石災害之發生區屬於大寮層中段塊狀砂岩，且為逆向坡之型態，現地調查結果顯示本區域具有兩組傾角近乎垂直之節理面，一組走向約略平行於海岸線，另一組走向則約略垂直於海岸線。致災成因可能與長期雨水入滲及風化作用有關，節理裂隙除因風化作用逐漸加大外，節理面上之含鐵質結核亦可能於風化後體積增加，進而加速節理開裂速度。本次落石災害之運動歷程大致可分為傾倒、滾動、墜落、彈跳、滾動等數段歷程，落石運動過程耗時約23 秒，移動路徑上之植被與風化土壤層可能為遲滯落石運動之主因。本文將說明此次災害之地質調查成果，並探討可能之破壞機制，以供未來類似災害之防治對策參考。Several rockfalls caused damages on Highway No.2 during an intensive rainfall on August 31, 2013, in Keelung. One of the rockfalls hit a car and the event was captured by a camera. This study analyzes the mechanism of the rockfall based on the video and field investigation. Two major joints which led to the hazard, one was parallel to the coast and the other was perpendicular to the coast. Both of them were almost vertical and cut the rock into several blocks. Weathering processes may have lead to the extension of joints during the heavy rainfall; the infiltration and the surface runoff took the weathered material away, making the rock unable and ultimately leading to the rockfall. The process of this hazard can be divided into topple, roll, fall, bounce and roll. The rockfall took about 23 seconds in total. This paper focuses on the results of field investigation and the mechanism of the rockfall is also discussed

The characteristics of geological environment along the New East-West cross highway (III)

By an onsite investigation, the largest debris flow in Taiwan’s history is analyzed in this paper. A heavy rainfall of 1748 mm/day occurred during typhoon Herb in the Hoser area at the end of July 1996. Aerial photo assessment and observations of geological and geomorphological features have contributed to our understanding of this massive destruction. Mechanisms of the hazardous debris flow are explored and discussed. Data revealed that the rock discontinuities were a major factor in the voluminous loose materials in the debris flows. The heavy and rapid rainfall instantly transported massive amounts of debris flow materials into the center and then quickly funneled them to the lower parts of gullies. The heavy slurry became an effective cutting device to erode the sidewalls and move large quantities of the debris materials to the end of the gullies.本文以現場調查之觀點來分析台灣 史上最大的土石流災害。1996 年7 月底， 賀伯颱風給和社地區帶來了1748mm 的日 降雨量。從航照圖的分析以及其他地質、 地貌表徵的調查工作有助於我們收集大量 的資料對於破壞現象的了解，而土石流災 害的機制也一併在現地調查工作中討論。 從現地調查的資料中顯示，岩石不 連續面的崩解，突然使得溝谷兩旁之地質 材料堆積於溝谷中，是造成本次災害的主 因。而大量及迅速的降雨，將這些堆積於 溝谷中的地質材料不停的運往下游。這些 瞬間形成的土石流不僅往下流動，也一面 對溝谷兩側的谷壁產生淘挖、沖蝕的現 象，並同時將兩側崩坍之土石匯聚於溝谷 中，一併往下面流動至溝谷底部