A History of Research and a Review of Recent Developments

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Structural loading from distant explosions
Figure 4.4 Relationship between drag coefficient ratio and solidity ratio for two
parallel trusses.
4.3 LOADS ON UNDERGROUND STRUCTURES
There are several ways in which a structure buried in soil can be loaded by
large and relatively distant detonated explosions. The structure may be buried
at a sufficient depth beneath the surface to escape the effects of air blast dynamic
pressures from large above-ground explosions. Structural loading can then
result from the surface pressures due to the instantaneous pressure rise in the
shock front, causing direct ground shock, or from air-induced ground shock
which arises from the passage of the shock front across the surface of the soil
above the structure. If the large explosion takes place on the surface of the soil
(a contact surface burst) the earth shock can travel directly through the soil
on its way to the structure. Direct earth shock can also emanate from an
explosion that occurs well below the surface of the soil.
Shallow or semi-buried structures, although covered with soil, can be partly
above ground level, and because of this can also be loaded by the blast winds.