Figure 6 shows some details of typical finite element results at various
frequencies of loading. The absolute acceleration at the top of the backfill
at a distance of 3.125 H away from the wall, the total force that acts on
the wall, the shear force at the base of the wall, and the permanent
displacement of the wall relative to the underlying soil are presented.
The permanent displacements from the rigid-plastic model, computed
by using a modified version of Zarrabi's model with a constant inclination
of failure plane in the backfill, are also presented. Sliding of the
wall occurs during those intervals when the shear force at the base of
the wall is at its maximum value of 21.6 kips/ft (315 kN/m), which is
determined by the weight of the wall and the friction angle between the
wall and underlying soil. Note, the maximum force between backfill and
wall occurs after slip stops. The time variation of total lateral force is a
complicated function of the input acceleration, the response of the backfill
and the occurrence of sliding. As may be seen in Fig. 6, for frequency
ratios up to 0.75 the response of the system becomes more or less stationary
after three cycles of loading, whereas for higher frequencies it
does not.