Environmental Engineering Reference
In-Depth Information
The existence of free surface increases the damage. In engineering explosion,
increasing the free surfaces is used to improve the ef
ciency of explosion.
(2) Throwing blasting [
21
]
When the packing mass of an explosive is increased and the explosive is closer
to the ground, once the energy of explosion is larger than the resistance of the media
above the explosive, the crushed rocks and soils are thrown upward in the shape of
a speaker. At the same time, a throwing blasting cone is generated, which is from
the explosion center to the ground (Fig.
2.37
).
In Fig.
2.37
, the vertical distance from the explosive center to the free surface is
the smallest resistant line, which is represented by W*. The radius of the blasting
cone is R.
Figure
2.37
also indicates that the throwing blasting is a process of rock and soil
transportation. After a single explosion or detonation, the position OA, which is the
smallest resistant line, protrudes
first, and the protrusion extends to the surrounding.
The lifted height and extending range increase following that time prolongs.
Though the height lifting continues, the range extension stops once it reaches a
certain range. This process is the bulging motion stage. The bulging breaking and
scattering stage is that the crushed rocks and soils move upward as an entirety,
when the lifted height reaches 1
2 times of the smallest resistant line, the top
bulging breaks, then the explosion products and rock and soil fragmentations scatter
upward together. The rock and soil fragmentations fly in air, and finally fall on the
ground under the impact of gravity. Part of fragmentations fall into the cone, and
part fall on the ground near the cone. Compared to the protrusion of the ground, this
cone is named
-
(Fig.
2.37
c). In the above stages of a single blasting explosion,
the bulging motion of rocks and soils has the maximum linear speed in the direction
of the smallest resistant line OA. The linear speed is smaller when it is farther away
from OA. And the speed of point B (the edge of the cone) is the smallest, zero.
When the rocks and soils are just thrown up, the sparse waves transport into
them because of the relatively lower surrounding pressure. At the same time, the
sparse waves crush the rocks and soils further. According to the throwing index n,
there are several explosion/detonation conditions, which are listed below.
“
rim
”
(1) n > 1 is the strong blowing blasting. The vertex of crater pit is larger than 90
°
W
Þ
(2) n = 1 is the standard blowing blasting. The vertex of crater pit is 90
ð
n
¼
R
°
(3) 0.75 < n < 1 is the weekend blowing blasting. The vertex of crater pit is
smaller than 90
°
(4)
n < 0.75 is the loose blasting. There are no rocks and soils to blow.
