The Richards and Elms' (R-E) model of the seismic behavior of gravity
retaining walls is identical to Newmark's sliding block-on-a-plane model
for the seismic behavior of earth dams and embankments (10). In the
R-E model, the wall and rigid wedge portion of the backfill are modelled
as the block, and the ground as the plane (Fig. 2). The wall-backfill system
has a limiting horizontal acceleration (Ng) towards the backfill, where
g is the gravitational acceleration and AT is a dimensionless parameter.
When the ground acceleration equals the limiting acceleration, the combined
effects of the increased lateral earth pressures and wall inertia
completely mobilize the available shear strength at the base of the wall. If the ground acceleration exceeds Ng, the wall begins to slip relative to
its supporting ground. The amount of slippage depends on the ratio N/
A of the limiting acceleration Ng to the peak ground acceleration Ag, the
duration of the strong ground motion and other characteristics of the
earthquake.