Chapter 3—Containing Underground Nuclear Explosions « 53
Figure 3-10—Radius of Decrease in Rock Strength
—_
—_—
“
Surface
Depth = 400 y>—
y
Observation
radius
165 Vy
Micro-fractions
Seismic
radius
500N/y_
Seismic measurements and measurements taken from drill-back samples indicate a seemingly contradictory (but in fact consistent) radius
of decrease in rock strength.
SOURCE: Office of Technology Assessment, 1989.
radii. The decrease in seismic shear velocity indi-
radii, seismic velocity measurements and strength
tests typically show no change from their pre-shot
decreased. At distances greater than three cavity
planes are occasionally seen when the tunnels are
continue to be low out to a distance of three cavity
cates that the rock has been stressed and the strength
values, although small disturbances along bedding