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The front concrete panels bulged out slightly at the center of the wall when
seen on plan view. The front concrete panels deflected outward as seen on the
side view.
The overall picture of deformation of the RE wall after detonation event
MD11-E2 suggests that the interaction between the blast wave and the RE wall
was as follows. When the blast wave arrives at the front of the RE wall, the
incident blast wave of compressional nature pushed the front concrete panels
inward as the concrete panels were hard and rigid. As the concrete panels were
pushed inward, the soil behind the concrete panel facings was compressed. The
soil mass behind the front concrete panel facings was vertically confined by the
concrete slab on top and laterally confined by the concrete panels at both sides.
During undrained dynamic loading, the volume of soil mass remains unchanged
because there can be no dissipation of excess pore water pressure. Therefore, the
soil mass expanded laterally when it was compressed from the front. As a result,
the first column of the side concrete panels was pushed outward. Based on
diffraction theory of blast wave loading on structures, after the shock wave strikes
the front wall of the structure, the shock front reaches the rear edge of the
structure and starts spilling down toward the bottom of the back wall. The
concrete panels were similar to rigid concrete wall. Hence, the back of the front
concrete panel facings began to experience increased pressures as soon as the
shock front had passed beyond and enveloped it through the diffraction process.
Consequently, the front concrete panels were pushed outward by this diffracted
wave. Therefore, there was significant outward displacement of the front concrete
panels.
Figure 9
shows the condition of the RE wall after detonation event MD11-
E3. The front panels of the RE wall collapsed, and the soil mass behind the wall
spalled out. The soil mass and the concrete panels fell out to the front of the wall.
The reinforcement strips at the upper layers were pulled out extensively from the
soil mass by the concrete panels that fell outward. Some of these reinforcement
strips were pulled out completely from the soil mass and rest on top of the soil
mass in front of the wall. These reinforcement strips were still firmly attached to
the concrete panels that fell out, as the connections between the reinforcement
strips and the concrete panels were still intact. However, the concrete panels were
detached from the reinforcement strips for the lower layers. Unlike the upper
layers, the connections between the reinforcement strips and the concrete panels,
which were anchored into the concrete panel, were separated from the concrete
panels. The connections and the reinforcement strips remained in the soil mass,
while the concrete panels broke up and fell outward to the front.
The mechanism of the blast wave interaction with the RE wall was similar
to the previous detonation. When the incident blast wave first struck the wall
front, it pushed the front panels inward and caused the soil mass to be
compressed. This was not damaging to the wall. But after the incident blast wave
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