The impact of the Chi-Chi Earthquake on Slope Stability --- A Case Study in the Chenyulan Watershed
Date Issued
2007
Date
2007
Author(s)
Wu, Yi-Ding
DOI
zh-TW
Abstract
The Chi-Chi Earthquake which took place on September 21, 1999, not only caused direct destructions from its fault movements, but also induced 26,000 landslides with a total area of 16,000 ha. This study will place emphasis on the residual effects of the seismic waves on slope stability.
The Chenyoulan Watershed where numerous landslides were induced by the Chi-Chi Earthquake was selected as the study site. Four typhoon events which occurred before and after the earthquake were selected as the study cases. The landslides which took place in each of the typhoons were interpreted from aerial photos and satellite images. The number and density of landslides in each geological formation were calculated, and the size, specific catchment area, slope, elevation and the distance to ridge lines of each landslide were analyzed. In addition, pseudo internal frictional angles for each geological formation at the time of each event were back calibrated by applying the infinite slope model and the related landslide information. The evolution of the slope stability after the earthquake was evaluated based on the rainfall and landslide characteristics of each event in addition to the changing behavior of the pseudo internal frictional angles.
The spatial distribution of the landslides was found related to the spatial pattern of rainfall at each typhoon events, i.e. the density of landslides increased with rainfall amount. Comparing the landslides triggered by Typhoon Herb and by the Chi-Chi Earthquake, the later are more susceptible to reoccurrence during Typhoon Toraji. It shows that the Chi-Chi Earthquake has more profound and lasting effect on slope stability in the Chenyoulan Watershed than heavy rains. The pseudo internal frictional angles of the weaker geological formation showed more fluctuation in pseudo internal frictional angles variation, which was postulated to be caused by their sensitivity to the rainfall variation.
Based on the pseudo internal frictional angles, the number and area of the new and reactivated old landslides in each event, it is concluded that the slope stability in the Chenyoulan Watershed was sharply reduced by the Chi-Chi Earthquake, and has not recovered its stability even in 2005. Further study on the residue effects of the earthquake on slope stability is recommended.
Subjects
集集地震
陳有蘭溪
無限邊坡模式
虛擬內摩擦角
the Chi-Chi Earthquake
the Chenyoulan Watershed
the infinite slope model
pseudo internal frictional angle
Type
thesis
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