Acceleration responses at the crests of slopes are
dependent on input wave frequency and location;
they are also functions of the plastic displacement
(or the robustness status) of the slope. The
amplification factor (Am), which is defined as the
ratio of the peak response acceleration at the slope
crest to the input peak base acceleration, increases
with increasing input wave frequency ( f ); it
decreases with increasing setback distance from the
slope crest, and with increasing plastic displacement
(or the extent of yielding) of the slope. Under a
plastic slope displacement of Dmax/Ht > 5.0–
5.9 3 102, the values of Am obtained at the slope
crest are less than unity, regardless of the input wave
frequency or the setback distance from the crest of
the slope.
2. The amplification factor (Am) obtained at the crest of
the slope shows nonlinear degradation with increasing
input ground acceleration (HPGA). The relationship
of Am to HPGA can be expressed using
logarithmic functions. These relationships shows
frequency-dependent behavior. Transitions from the
state of amplification towards the state of deamplification
at the crest of the slope consistently
precede the critical collapse state of the slopes. At
this transitional state, plastic slope displacements of
Dmax/Ht ¼ 0.25–5.9 3 102 occur.
3. The resonant acceleration response at the crest of the
slope does not need to be considered in the stability
evaluation at yield, or post-yield, for a slope with
Dmax/Ht . 5.0–5.9 3 102. For the at-yield or postyield
states of the slope, a measurable plastic slope
displacement, associated with major failure planes in
the backfill, occurs. A de-amplification state at the
slope crest is dominant at this stage of shaking. On
the other hand, the resonance acceleration response
at the slope crest is a major factor to be considered
in the seismic stability evaluation for a reinforced
slope with small plastic slope displacements of Dmax/
Ht < 0.25 3 102.