| Summary: | 碩士 === 國立中央大學 === 土木工程學系 === 106 === This field study is located at the Houyenshan of San Yi, Miaoli, Taiwan, and the influence of five debris flow events on landforms in 2017 is analyzed. The whole terrain of Houyenshan has been silted up since October 2012, but only the slope of the upper reach increased, and the threshold of rainfall intensity for debris flows in the Houyenshan area declines. The rainfall characteristics of the eight debris-flow events from 2016 to 2017 have been analyzed, and the important factors affecting the moving distance of debris flows are summarized. The deposition angles for debris flows are generally within the range of 10.8 to 11.8 degrees. The ground motion velocities caused by debris flows are measured by two three-dimensional Geophones. The main vibration frequencies of the debris flows are between 15 - 40 Hz. The velocity thresholds of Station Geo1 in Z, Y, X directions are 20, 50, 4000 μm/s, respectively. While the thresholds of all directions of Station Geo2 are 20 μm/s.
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