Geoscience Reference
In-Depth Information
This was followed by a negative phase with duration longer than the positive
phase duration and characterized by a pressure below the ambient pressure.
The dynamic pressure registered was highest at P1 (
160 kPa), followed
<
by P2 (
10 kPa). This variation of dynamic pressure at
different total pressure cells may be due to different depths behind the facing of
the RS wall where the total pressure cells were installed. The depth behind the
facing of RS wall for total pressure cells P1, P2, and P3 was 0.5m, 2m, and 3.4m,
respectively. The largest dynamic peak total pressure was recorded at P1, which
was closest to the facing of the RS wall, followed by P2, which was farther away
behind the facing of RS wall, and P3, which was farthest away behind the facing
of RS wall. Although total pressure cell P1 was not at the same elevation as P2
and P3, the dynamic pressure was not affected because the blast wave front was
likely a uniform plane when it reached the RS wall. This shows that the peak
dynamic pressure due to the detonation of a 300-kg charge of TNT 15m away can
be effectively reduced from approximately 160 kPa to 10 kPa by a soil mass of
thickness roughly equal to 3.5m. Furthermore, the RS wall can withstand a peak
acceleration of about 20,000 g without much deterioration. Hence, with the
use of a geotextile reinforced soil wall, the blast incident pressure can be
reduced significantly and yet the wall was stable and can be subjected to
multiple blasts.
At the construction stage and one week after complete construction, strain
gauges of geotextiles in the RS wall registered stains from 1% to 3% in
geotextiles layer 2, 5, and 8, for both machine and cross-machine direction. For
all the blast events in the field, these strain gauges registered additional strains of
less than 0.2%, with the larger strains near the blast front of the RS wall. From the
instant of blasting and the next 200 ms, the strain gauges did not register any
significant changes. This shows that the geotextile reinforcement was not
subjected to additional tension during blast, which implies that the factor of
safety from static design for the geotextile reinforcement in the RS wall is
adequate.
Figure 11
shows the accelerometer (A1) and total pressure cells (P1 to P3)
responses during detonation event MD5-E2. The accelerometer A1 registered a
peak instantaneous acceleration of approximately 5000 g about 20 milliseconds
after the detonation. Although the detonation was closer to the RS wall, this
acceleration was lower than that for detonation event MD5-E1 because
the charge mass was smaller, only 110 kg compared to 300 kg of event
MD5-E1.
The total pressure cells P1, P2, and P3 registered peak dynamic pressures
(compressive) of approximately 110 kPa, 50 kPa, and 8 kPa, respectively, about
35 milliseconds after the detonation. The response of the total earth pressures
with time for all the total pressure cells during blast was similar to the free-field
pressure-time history. Again, the results of this event shows that the peak
120 kPa) and P3 (
<
<
Search WWH ::
Custom Search