Chapter 3—Containing Underground Nuclear Explosions ¢ 53
Figure 3-10—Radius of Decrease in Rock Strength
—
—_
——<—
— en,
—
“
“XN
Surtace
Depth = 400 y—-
La
y
Observation
radius
165 Vy
Micro-fractions
Seismic
radius
s00\/y
Seismic measurements and measurements taken from drili-back samples indicate a seemingly contradictory (but in fact consistent) radius
of decrease in rock strength.
SOURCE: Office of Technology Assessment, 1989.
continue to be low outto a distance of three cavity
radii, seismic velocity measurements and strength
radii. The decrease in seismic shear velocity indi-
tests typically show no change from their pre-shot
decreased. At distances greater than three cavity
planes are occasionally seen when the tunnels are
cates that the rock has been stressed and the strength
values, although small disturbances along bedding