Post-Earthquake Investigation of Several Geosynthetic Reinforced Soil Retaining Walls and Slopes During Ji-Ji Earthquake of Taiwan - Reinforced Soil Engineering: Advances in Research and Practice - page 291

the design of modular block walls for the National Concrete Masonry Association
(NCMA, Collin, 1997).
The design manual issued by the Federal Highway Administration
(FHWA) has also included seismic design procedure (Christopher et al., 1990;
Elias and Christopher, 1996) and has been made available for computerized
design (Leshchinsky, 1999). FHWA procedure was centered for the reinforced
soil structures with metallic reinforcements.
The previous earthquakes that occurred in the United States and Japan had
proved that geosynthetic reinforced soil structures are durable to minor and major
shakings (Elihau and Watt, 1991; Collin et al., 1992; Sandri, 1997; White and
Holtz, 1997; Tatsuoka et al., 1995, 1997). However, most reinforced soil
structures were subject to minor shaking except for the 1995 Kobe earthquake.
The reinforced soil structures found around the Kobe area had a rigid facing,
which is different from most geosynthetic reinforced soil retaining walls
available in other parts of the world. Moreoever, the modular block reinforced
soil retaining walls, an increasingly popular structure in North America, were not
constructed in Japan. Thus, the 1999 Ji-Ji earthquake in Taiwan provided an
opportunity to evaluate the seismic performance of geosynthetic reinforced soil
structures, particularly the modular block walls.

3 JI-JI (CHI-CHI) EARTHQUAKE AND PERFORMANCE OF
REINFORCED SOIL STRUCTURES

The Chi-Chi earthquake occurred on September 21, 1999, at 1:47 a.m., with a
magnitude of 7.3. More than 2200 people were killed, and devastating damage
was recorded. The main shock was recorded at 23.87 8 N, 120.75 8 E in central
Taiwan, at a depth of 7 km (Lee, 1999). The rupture surface observed at the
Chelungpu fault extended for more than 85 km, with a vertical displacement of
1 to 6 m (Fig. 1) . The maximum horizontal peak ground acceleration was
recorded for over 1 g. The ratio of vertical to horizontal acceleration was large.
For example, at station TCU129, 13.5 km from the epicenter, the E-W, N-S,
and vertical (U-D) accelerations were 983 gal, 611 gal, and 335 gal,

respectively.
Seismic design is conducted for the buildings and highway structures in
Taiwan. The main island is divided into 4 main seismic zones: I-A, I-B, II, and III
(Fig. 2) . The respective accelerations used for design are 0.33 g, 0.28 g, 0.23 g,
and 0.18 g. It is obvious that the recorded accelerations, such as that at station
TCU129, far exceeded the design values.
The investigation on the performance of several geosynthetic reinforced
soil structures was conducted on January 28 and 29 around central Taiwan.
Although most severely damaged buildings have been demolished, many soil