Journal of the Japan Society of Erosion Control Engineering, Vol.58,No.1,2005
Relationship between slope failures and precipitation before and after
the Chi]chi Earthquake investigated using long]term repair records of forestry
roads
in the National Taiwan University Forest
Norifumi HOTTA Yi]huei KAN Yasuhiro SHUIN
Tsong]Huei WEI Zhen]Sheng ZHANG
Hsin]Hsiung CHEN Masakazu SUZUKI
Abstract
This study examined the relationship between slope failure and precipitation using
long]term data for the Chitou tract, which is in the Experimental Forest of National
Taiwan University, located 20 km south of the Chi]chi Earthquake epicenter. The
University Forest maintains a variety of records that are a useful source of long]term
data. Repair records for forestry roads, which assure long]term uniformity of
temporal data owing to the high priority given to repairing forestry roads, were
used to discuss the characteristics of slope failure. The relationship before
and after the earthquake was compared to clarify the indirect influence of the
Chi]chi Earthquake on subsequent slope failures. As a result, we showed that the
earthquake affected subsequent slope failures, although the earthquake itself
caused no slope failures directly when it happened on 21 September 1999. After
the earthquake, the first slope failure was triggered by a precipitation event
involving 91.5 mm of rain over 5 days in February 2000. By contrast, the smallest
precipitation event that triggered slope failure before the earthquake was 210.5
mm over 5 days. In July 2001, the second slope failure event following the earthquake
set a record for the most slope failures in the history of the Chitou tract. By
the time of the slope failure event in May 2002, the earthquake no longer had
any notable influence.
Key words:Chi]Chi Earthquake, slope failure, University Forest, forestry road
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