ABSTRACT
When an explosive charge detonates in contact with an unyielding surface, in perfect conditions the shock wave in theory has a hemispherical wavefront, as shown in Figure 2.1, and not the spherical wave front of an explosion in free air. The energy of the explosion is therefore concentrated over a smaller total surface area, and theoretically all the relationships discussed so far for free-air bursts will still be valid if twice the charge weight (2 W) is substituted for W in the equations. However, if the earth is yielding and capable of absorbing part of the energy, the factor of 2 on charge weight must be judiciously reduced. Experiments suggest it is nearer 1.7, as discussed below.
