Model Tests of Seismic Stability of Several Types of Soil Retaining Walls - Reinforced Soil Engineering: Advances in Research and Practice - page 320

formed almost simultaneously during irregular shaking. In particular, for the
reinforced-soil type 2 (Fig. 9), the upper failure plane developed from the heel of
the backfill zone reinforced with short reinforcement layers and stopped
somewhere below the longest reinforcement layer located near the backfill
surface. On the other hand, as shown in Fig. 9, it is very likely that the lower
failure plane reached the surface of the backfill. This inference is supported by the
observed amount of wall displacements at the moment when failure planes were
formed. The location of the lower failure plane was governed by the existence of
the longest reinforcement layer.
6.2 Angle of Failure Plane
The angle of failure plane adefined from the horizontal direction was evaluated
by carefully removing the backfill surrounding the central layers of black-dyed
Toyoura sand. The angle was taken at the failure plane developing from the
bottom of the back wedge in the backfill (i.e., in the unreinforced zone for the
reinforced soil walls). For the leaning- and gravity-type RWs in the irregular
shaking tests, as shown in Fig. 6b and c, the formation of the deeper (second)
failure plane and associated deformation of backfill located above it slightly
changed the angle of the shallower (first) failure plane that has been previously
formed. In these cases, the a-values of the shallower failure planes were
corrected to those for the initial wall configuration (before deformation). In so
doing, it was assumed that the initial failure plane was formed at the same time at
the side wall and at the center part of the backfill.
In Fig. 10 , the values of the failure plane angle a are plotted versus the
seismic coefficients (k h ) fp for the shaking step when the respective failure plane
was formed. For comparison, results from the static tilting tests and the sinusoidal
Figure 9 Comparison of locations of failure planes and longer reinforcement layers for
reinforced soil retaining wall type 2.