A History of Research and a Review of Recent Developments

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Structural loading from local explosions
Figure 5.3 Schematic view of part of a line charge array (from Baker et al., ref. 5.2).
surface blast loading. This type of arrangement has a military use connected
with the rapid clearance of a lane through a minefield. Experiments on the
blast output from a pair of parallel Primacord line charge arrays have been
reported by Baker et al. [5.2], in which reflected pressures and ground impulses
were measured at various distances from the arrays. Relationships between
charge weight, line spacing and stand-off distance were analysed and scaling
laws developed. In Figure 5.3, taken from the report, two identical line charges
are shown, distance R above the ground, with a charge spacing of S. The
model test conditions ranged from S=1.5 in, R=2 in, using 40 gram/foot
Primacord, to S=9 in, R=16 in using 400 gram/foot Primacord. The greatest
loads in the region below the charges occur when a Mach stem forms and
charge spacings and stand-offs to achieve this formation were measured. The
results are summarized in Figure 5.4, which compares scaled stand-off distance
(R/W 1/3 ) and scaled charge spacing (S/W 1/3 ) at which a fully formed Mach
stem is produced. At lesser stand-offs or spacing the pressure/time curve at
Figure 5.4 Position of parallel line charges to produce fully formed Mach stem on
the ground surface (from Baker et al., ref. 5.2).