For all of the models, the major failure mode of the walls was overturning as shown
in Figure 1. It is seen from Figure 6 that the outward displacement measured by displacement
transducer D1 near the bottom of the reinforced soil, Type 1 wall facing, was
much smaller than that near the top of the facing measured by displacement transducer,
D3. This indicates that the transitional component of the facing displacement was much
smaller than its rotational component. It should be also noted that the subsoil immediately
in front of the facing suffered a slight heaving, as measured by displacement transducer
D4, which is possibly due to the occurrence of bearing capacity failure in the subsoil
below the facing.
In order to compare the relative stability of different wall types, the observed critical
accelerations were defined as the amplitude of the base acceleration (measured by accelerometer
A11 in Figure 6) in the active state (corresponding to negative acceleration
values in Figure 6) when the outward displacement at the top of the facing reached 5%
of the total wall height (approximately 25 mm). Note that, after the outward displacement
at the top of the facing exceeded 5% of the total wall height, the displacement began
to increase in an uncontrollable manner as was typically demonstrated by displacement
transducer D3 in Figure 6.
In Figure 14, the observed critical seismic acceleration coefficients, kh-cr(obs) , are
compared with the predicted critical seismic acceleration coefficients, kh-cr(cal) , which
resulted in a factor of safety of unity against overturning for δ = 3/4φ. For this comparison,
accelerations (see Table 1 for the observed critical accelerations) were converted
to seismic coefficients by using Equation 1.
For the cantilever-type, leaning-type, and gravity-type model walls, the observed values
were almost equal to or smaller than the predicted values against overturning. The
relative difference was larger in the order of the gravity-type, leaning-type, and cantilever-type
walls. The smaller observed critical seismic coefficient for the gravity-type
and leaning-type walls may be related to the inference that, as mentioned in Section 3,
the interface friction angle δw activated between the backfill and the wall facing was
smaller than the interface friction angle activated along the virtually vertical back face
within the backfill of the cantilever-type wall. On the other hand, the observed value
was slightly larger than the predicted value for the reinforced soil, Type 1 model wall,
and noticeably larger for the reinforced soil, Type 2 model wall.
The larger observed critical seismic coefficients for the reinforced-soil walls may be
due to the difference in the location of center of rotation (Section 3); i.e. the center of
rotation moves away from the wall face into the backfill after the bearing capacity failure
of the subsoil below the facing in the case of the gravity-type, leaning-type, and
cantilever-type walls. The distance of the same point of rotation from the back of the
wall is less in the case of the reinforced soil walls due to the flexibility of the backfill.
For all of the models, the major failure mode of the walls was overturning as shownin Figure 1. It is seen from Figure 6 that the outward displacement measured by displacementtransducer D1 near the bottom of the reinforced soil, Type 1 wall facing, wasmuch smaller than that near the top of the facing measured by displacement transducer,D3. This indicates that the transitional component of the facing displacement was muchsmaller than its rotational component. It should be also noted that the subsoil immediatelyin front of the facing suffered a slight heaving, as measured by displacement transducerD4, which is possibly due to the occurrence of bearing capacity failure in the subsoilbelow the facing.In order to compare the relative stability of different wall types, the observed criticalaccelerations were defined as the amplitude of the base acceleration (measured by accelerometerA11 in Figure 6) in the active state (corresponding to negative accelerationvalues in Figure 6) when the outward displacement at the top of the facing reached 5%of the total wall height (approximately 25 mm). Note that, after the outward displacementat the top of the facing exceeded 5% of the total wall height, the displacement beganto increase in an uncontrollable manner as was typically demonstrated by displacementtransducer D3 in Figure 6.In Figure 14, the observed critical seismic acceleration coefficients, kh-cr(obs) , arecompared with the predicted critical seismic acceleration coefficients, kh-cr(cal) , whichresulted in a factor of safety of unity against overturning for δ = 3/4φ. For this comparison,accelerations (see Table 1 for the observed critical accelerations) were convertedto seismic coefficients by using Equation 1.For the cantilever-type, leaning-type, and gravity-type model walls, the observed valueswere almost equal to or smaller than the predicted values against overturning. Therelative difference was larger in the order of the gravity-type, leaning-type, and cantilever-typewalls. The smaller observed critical seismic coefficient for the gravity-typeand leaning-type walls may be related to the inference that, as mentioned in Section 3,the interface friction angle δw activated between the backfill and the wall facing wassmaller than the interface friction angle activated along the virtually vertical back facewithin the backfill of the cantilever-type wall. On the other hand, the observed valuewas slightly larger than the predicted value for the reinforced soil, Type 1 model wall,and noticeably larger for the reinforced soil, Type 2 model wall.The larger observed critical seismic coefficients for the reinforced-soil walls may bedue to the difference in the location of center of rotation (Section 3); i.e. the center ofrotation moves away from the wall face into the backfill after the bearing capacity failureof the subsoil below the facing in the case of the gravity-type, leaning-type, and
cantilever-type walls. The distance of the same point of rotation from the back of the
wall is less in the case of the reinforced soil walls due to the flexibility of the backfill.
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