| Summary: | 碩士 === 國立交通大學 === 土木工程系所 === 104 === One observes that many slumps usually happen in the tribal site, Luchang, Miaoli. Based on the results of the field investigation, we find that the top soil is composed of the eroded thick colluvium; the roads are cracked and subsided;the retaining walls are damaged; and the buildings are leaned in this site. In this study, the interpretation of aerial photographs and historical maps are adopted to analyze and show the impact of the geological on slope instability, the geomorphological change, and the rate of river incision of the Luchang River near the east slope of studied site. Also, the effect of this river incision on the slope stability of the study site would be investigated in detail.
From the results of aerial photograph interpretation, we find that there are two major past slope failure events in the area between 1980-2009. Moreover, the events caused the road damages and the slope fractures under Luchang area reveals fractures that result from the effect of suspected tensions. In this situation, rocks under the major ridge would fall and taluses would increase proportional to time. Besides, it is found that, from the 1980’s aerial photographs, many colluviums under the slope of Luchang area have been probably formed in an ancient period (not an age dating of information). It could lead the area into instability. Based on the discussions above, the study site shows its instable status.
Because the top of east slope is composed of thick colluvial deposits and the shear strength decreases due to the infiltration by heavy rain, this leads the cover of thick colluviums to erode away. For the steep cliff under the major ridge, it can make the whole situation instable because the lithology belongs to a kind of layered sedimentary rocks. According to the effect of differential erosion, hard rocks would be overhung and easily fall down when heavy raining.
Keywords: aerial photographs, historical maps, slope instability, geomorphological change, river incision.
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