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deadly to human occupants. However, no flying debris was produced when blast
fragments cut the geotextile facing.
During detonation event MD5-E2, all strain gauges in the RS wall did not
register any significant changes. In addition, there was also no significant
deformation of the RS wall. This implies that the geotextile reinforcement was
not subjected to additional dynamic strain during and after detonation. However,
there was extensive outward deformation of the RE wall front and side panels
after detonation event MD11-E2. Hence it may be deduced that additional tension
developed in the reinforcement strips during and after detonation. This
comparison implies that the stability of the RE wall was greatly affected by the
blast loading whereas the stability of the RS wall was not much affected. This
difference in the behavior of the two wall systems was mainly due to the different
facing materials. Geotextile facing was flexible and porous enough for the blast
wave to pass through, whereas the concrete panel facing was like a rigid wall
where the wave diffraction process would occur when the blast waves envelop
the wall and pass around it. The diffracted wave caused the pressure on the back
of the wall to increase and pushed the wall outward to the front.
After detonation event MD5-E3, larger areas of geotextile facing were
melted and cut by fragments, but there was still no significant deflection or
bulging of the RS wall facing. However, after detonation event MD11-E3, the
front panels of the RE wall collapsed and the soil mass behind the RE wall fell
out. The reinforcement strips at the upper layers were pulled out extensively from
the soil mass by the concrete panels that fell outward. At the lower layers, the
connections between the reinforcement strips and the concrete panels, which
were anchored into the concrete panel, were sheared away from the concrete
panels. This clearly illustrates the disadvantage of using rigid concrete panels as
facing material compared to flexible facing material such as geotextile. Another
distinct advantage of geotextile sheet reinforcements compared to metallic strip
reinforcements is that the larger contact area of geotextiles with the soil made
dynamic pullout failure less likely in the RS wall as compared to the RE wall.
Thus the RS wall gave a better composite reinforced structure than the RE wall.
5 INSTRUMENTATION RESULTS FOR THE RS WALL
Figure 10
shows the accelerometer (A1) and total pressure cells (P1 to P3)
responses during detonation event MD5-E1. The accelerometer A1 registered a
peak instantaneous acceleration of approximately 20,000 g at about
20 milliseconds after the detonation. The total pressure cells P1, P2, and P3
registered peak dynamic pressure (compressive) of approximately 160 kPa,
110 kPa, and 10 kPa, respectively, at about 35 milliseconds after the detonation.
The response of the total earth pressures with time for all the total pressure cells
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