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observed in the sinusoidal shaking tests. In addition, these ratios were
different among the different types of RWs.
4. These facts suggest that the dynamic stability of RWs is not totally
controlled by “peak base acceleration”/g, but also by other dynamic
factors such as the duration of peak lateral force acting on the backface
of wall, phase lag and amplification of response acceleration, dynamic
ductility and flexibility of RWs, and dynamic shear deformation of
backfill, especially for the reinforced soil-type RWs with longer
reinforcements. Effects of those dynamic factors should not be ignored
for proper seismic stability analysis of RWs.
5.
In the sinusoidal and irregular shaking tests, the observed values of
(k
h
)
ult
were similar between the reinforced soil-type 2 RW having a
couple of long reinforcement layers at high levels in the backfill and the
reinforced soil-type 3 RW having moderately long same-length
reinforcement layers. On the other hand, the total amount of
reinforcements was smaller with reinforced soil-type 2 RW. When
reconstructing existing slopes to vertical reinforced soil-type RWs
having an FHR facing, the use of relatively short reinforcements at low
levels is preferred to minimize the amount of slope excavation. Based
on the test results described above, using several long reinforcement
layers at high levels, as reinforced soil-type 2 RW, can be
recommended to effectively increase its seismic stability.
Figure 24
compares the respective calculated critical seismic coefficient
(k
h
)
cr
against sliding with those against overturning and bearing capacity failure.
With cantilever- and gravity-type RWs, the (k
h
)
cr
-value against overturning (solid
symbols) was larger than that against bearing capacity failure (open symbols), and
in the following comparison, therefore, the latter value was employed.
For leaning-type and reinforced soil-type 3 RWs, the calculated value of
(k
h
)
cr
against sliding failure was marginally smaller than the respective value
against overturning or bearing capacity failure. On the other hand, for the other
RWs, the calculated values of (k
h
)
cr
against sliding failure were larger than those
against overturning or bearing capacity failure, whichever was smaller. For
leaning-type RW, the above result is consistent with the fact that the observed
failure mode consisted not only of overturning but also of sliding
(Fig. 6c)
.
Such
behavior can be also seen from
Fig. 25,
where the residual overturning angle of the
facing at the end of each shaking step is plotted versus the residual sliding
displacement, which were evaluated from records of two displacement
transducers set near the top and bottom parts of the facing. It should be noted,
however, that these (k
h
)
cr
-values against sliding should be treated with caution,
because these values are too sensitive to the friction angle at the interface between
the wall base and the subsoil layers (except for the reinforced soil-type RWs).
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