the same general geologic conditions.
This washing action would then take on a similar
role to throwout or fallout in defining the phenomena. It would be highly desirable to separate the water-actuated effects from the direct blast-produced crater, but this capability
is not yet a reality. Considering the operational difficulties of obtaining early-time crater
measurements, a realistic approach would compare craters only when the ground or ground-
water conditions are similar and include such induced phenomena as washing action into the
definition of the apparent crater, since this induced effect is properly a part of the immediate recovery problem. The water-actuated effects are then a part of the weapon effects
for these burst conditions. However, these effects complicate the correlation, scaling,
or complete understanding of cratering phenomena from a technical point of view.
Several other factors affect the analysis of data obtained during this project and correlation with data obtained in the past. Ideally speaking, four variables determine the size
of the crater from a near-surface detonation of an explosive charge. These are total blast
yield, height above or depth below the air-earth interface, energy partition, and soil type.
Knowing the relationships of these variables, the volume of a crater and the ratio of its
radius to its depth should be calculable.
For a nuclear surface burst, the portion of the hydrodynamic yield that manifests itself
in cratering and ground shock can be evaluated on a TNT-equivalent basis by considering
the ratio
Weight of TNT required to produce a given crater dimension
Hydrodynamic yield to produce the same crater dimension.
The use of the TNT equivalent allows high-explosive cratering data to be convertedinto
prediction curves for nuclear weapons.
A drawback to this method is the fact that there is little high-explosive data for comparison, both from the point of view of soil type found at the EPG and the high yields necessary for direct comparison.
Griggs (Reference 4) predicted for the Operation Jangle surface shot with good accuracy,
calculating that only about 2 percent of the total energy release will go into the ground for
a nuclear detonation on an air-cround planarinterface. Other estimates by Porzel (Reference 1) indicate about 0.1 percent for EPG soil and 0.6 percent for the more porous
Nevada Test Site (NTS) soil.
The saturated soil at the EPG cannot be expected to absorb
and transmit energy in the same manner as the NTSsoil with its high air content (about
40 percent by volume). The NTSsoil will react plastically, whereas the saturated soil at
the #PG is considered cssentially incompressible.
1.4
MILITARY SIGNIFICANCE
Craters from nuclear explosions can be an extremely important weapon effect. There
are certain target types, both surface and subsurface, that require a contact (i.e., a
cratering) burst tu cause significant damage. Massive concrete fortifications, underground
structures, heavy industrial machinery, airfield runways, tunnels, and dams are good examples of this type of target. Probably just as important, tactically speaking, is the ability
to achieve delaying action to an enemyby the use of craters, crater lips, and their high
residual contamination as barriers.
If a crater is to be used as an obstacle, or part of a barrier system, its effectiveness
is dependent upon the ratio of its radius to depth or the slope of its sides. Previous data
indicate that for a surface burst as the yield increases so does this ratio, and as the depth
10