Dynamic Simulation of the Reinforced Slope Failure at Chi-Nan University During the 1999 Chi-Chi Earthquake - Reinforced Soil Engineering: Advances in Research and Practice - page 466

Major factors, however, playing a role in the failure of the reinforced slope are
summarized as follows:

1. The peak acceleration on the east -west direction is up to 0.58 g, which
is much greater than the local earthquake-resistant design criterion
(a max ¼ 0.23 g).

2. Soil placed on the back of the reinforced slope was recompacted
materials since the slope collapsed in 1995. The strength of backfill on
the back of the reinforced slope is less than that of existing gravel
stratum. Slope instability may occur much easier in the unreinforced
backfill than in the undistributed gravel stratum in the seismic
condition.
3. The geologic weak plane locating on the up slope of the reinforced
slope may have a direct link with the failure of the reinforced slope
during the earthquake. The weak plane is considered as a trigger for the
failure of the reinforced slope. Soil mass above the weak plane moves
along the plane during the Chi-Chi earthquake.
4. The reinforcement length of the reinforced slope is short compared to
the height of the reinforced slope. Reinforcements of the reinforced
slope at each tier are different in length. The reinforcement is 4m long
on the top tier of the reinforced slope and increases gradually to 13 m
long on the bottom tier of the reinforced slope. The reinforced slope,
however, is as high as 40m. The ratio of average reinforcement length
of height of reinforced slope at the failure site is just 0.2, which is much
lower than normally acceptable ratios in practice (i.e., 0.6 to 1.0). Thus,
the stability of the reinforced slope at the failure site may be on the
margin of critical condition in normal condition. The Chi-Chi
earthquake may be just

the trigger blamed for the failure of the

reinforced slope.

7 CONCLUSIONS

The study of a failed reinforced slope, with a height of 60 to 70m, induced by the
Chi-Chi earthquake is conducted in this chapter. The reinforced slope itself is
arranged in four tiers, which is 10 m high for each tier, and is located on the
middle part of a cut slope. The slope angle of the reinforced slope is 60

. Field
investigation, survey, geologic exploration, laboratory tests, and dynamic
simulation of the reinforced slope are carried out. Although the Chi-Chi
earthquake has been the most severe earthquake during the past 100 years in
Taiwan, geologic conditions at the site and some design aspects may also have
played a role in the failure of the reinforced slope. Dynamic simulation of

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