"Since 1952 eight nuclear explosions have been fired underground at the Atomic Energy Commission's Nevada Test Site. The explosions have varied in energy release from 55 tons to 19,000 tons of TNT equivalent and were carried out at depths varying from shallow burial to produce cratering to those depths at which no visible effects appeared on the surface. The major experimental data from these explosions, as well as the phenomenology of the deeper shots, is summarized here."
UCRL-5626; University of California Radiation Laboratory-5626
U.S. Dept. of Energy, Office of Science and Technical Information: http://www.osti.gov/