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 454

1 INTRODUCTION

The Chi-Chi (also known as Ji-Ji in English) earthquake, with a Richter scale
of 7.3, hit the central part of Taiwan at 1:47 a.m. on September 21, 1999. The
earthquake caused devastating damage to campus buildings and reinforced
slope failure at the National Chi-Nan University in Pu-Li, which is
approximately 20 km northeast from the epicenter of Chi-Chi. This chapter
analyzes the mechanism of the failure in terms of design aspects, seismic
intensity, geological condition, and so forth. In addition, dynamic simulation
of failure during the earthquake was performed using the finite-element
software PLAXIS.

2 DESCRIPTION OF THE COLLAPSED REINFORCED
SLOPE

The collapsed reinforced slope is on the middle part of a cut slope, which is
60 to 80m high. The collapsed area covers an alignment 180m long. Pictures
of the collapsed reinforced slope induced by the earthquake and topographic
condition are shown in Figs. 1 and 2 , respectively. The failed area is also
shown in Fig. 2. The reinforced slope itself is arranged in four tiers, 10 m
high for each tier. The profile of the reinforced slope prior to and after the
Chi-Chi earthquake is shown in Fig. 3 . According to the field investigation,
tension cracks were identified at the overlap portion of the reinforcement, and
backfill overflowed between overlaps.
Reinforcements of the reinforced slope at each tier are different in length.
The reinforcement is 4m long on the top level of the reinforced slope and
increases gradually to 13 m long on the bottom level of the reinforced slope, as
shown in Fig. 3. Vertical spacing of the reinforcement 1 m, and the overlapping
length of reinforcement for wraparound is 1.7m. Some of the reinforcements for
wraparound were pulled out at the site.

2.1 Previous Slope Failure at the Site

Previous slope failure at the site took place during construction of the
reinforced slope in 1995. Shown in Fig. 4 is the collapsed slope in 1995. A
failure plane with hard yellowish clayey material on the back of the
reinforced slope can be clearly identified at the site. The clayey material has a
thickness of 2 to 3m according to the field investigation of the failed slope
and is considered as a weak plane for the slope. The weak plane has a slope
angle of 30 E in strike. In other words, the

failed slope is considered a dip slope. The slope failure, in 1995 was induced

8 to 35 8 toward east and is N30 8