Critical acceleration is important as a measure of stability after which the dynamic factor of safety will
be less than one, and permanent displacement will be induced. As shown in Fig. 7, for gravity-type
RW, the displacement-acceleration curves were bi-linear clearly. That is, deformation was small until
434 gal, after which deformation was suddenly increased. Thus the value of 434 gal could be
considered the model specific critical acceleration value.
However, the determination of critical accelerations for geogrid-RS RW and geocell-RS RW is not
so clear, since they showed a gradual increase in the displacements as the increase of base acceleration.
In this study, the critical accelerations of geogrid-RS RW and geocell-RS RW were determined at the
time when the initial failure plane was observed in the backfill, which were indicated as the red
vertical arrows in Fig. 7. Thus, for geogrid-RS RW and geocell-RS RW, the critical accelerations were
711 gal and 768 gal, respectively, after which the displacement increased sharply associated with
progressive failure until the full formation of the failure planes at 790 gal and 876 gal (black vertical
arrows shown in Fig. 7), respectively. Note also that the determined critical accelerations generated a
cumulative displacement of 8.18% of the wall height for geogrid-RS RW and 7.53% for geocell-RS
RW which were calculated at the top of model walls. Table 1 summarized both the timings of initial
and full formation of failure planes based on observation, showing that geocell-RS RW has a higher
seismic performance than geogrid-RS RW and gravity-type RW in terms of strength (i.e. base
acceleration at the time of formation of failure) and corresponding deformation characteristics (top
wall displacement).