JANUARY—DECEMBER 1963
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The most promising industrial applications for contained nuclear
explosions are those involving the development of our natural resources. These concepts include breaking up ore bodies for mining by
block caving or in-situ leaching methods; producing crushed rock
for large construction projects, and fracturing gas and petroleum
bearing rock formations to increase production or make production
possible from otherwise unrecoverable reserves.
Phenomena of Contained Explosions
Understanding of the phenomena associated with contained ex-
plosions is based upon empirical studies of past detonations, develop-
ment of instrumentation to follow explosion history from detonation
through cavity growth to cavity collapse, and development of theory
and computational techniques to handle the data.
Geological studies of the post-shot environment andtheir interpretations have yielded significant results. Maximum cavity radii were
determinedfor 35 explosions, and a method for predicting cavity radii
as a function of yield and depth of explosion has resulted. Such radii
now can be predicted within 10 percent for any single rock type.
Furthermore, experience in tuff, alluvium, salt, and granodiorite shows
that the rock type affects the cavity radii by only 20 percent. The
cavity usually collapses shortly after formation. In the case of Gnome,
however, relatively little of the cavity has collapsed because the salt
formation was strong and plastic enough to arch without breaking.
However, in the case of tuff and granodiorite, a chimney of broken
rubble is formed after cavity collapse. The chimney of broken rock
is roughly cylindrical and extends above the shot point to a height of
about 5 times the original cavity radius, if the detonation is of a sufficient depth. Cavities formed from detonationsin alluvium havecollapsed within a few minutes. In alluvium a depression crater is
created at the surface almost immediately after cavity collapse.
Special instruments have been developed and used to measure shock
effects of underground explosionsin tuff, alluvium, granodiorite, and
salt. The peak shock pressure, the velocity of the shock wave, and the
velocity of the material behind the shock wave have been measured
as a function of the time. Two instruments, developed during the
past year, are noteworthy. One of these is a small, inexpensive gauge
to measure the peak pressure found in a shock wave 20 to 80 feet from
a typical undergroundnuclear detonation.
The other instrument is a gauge that measures continuously the
velocity of the shock front at distances up to 400 feet from the detona-
tion point. A cable is strentched down a hole pointing toward the
center of detonation, As the shock wave spreads out from the ex-