Civil Engineering Reference
In-Depth Information
10
(70)
B
Surface
1
(7)
Charge
W
B/
3
W=0
0.1
(0.7)
W=
1
2
B/
3
B/
3
W=1
0.01
(0.07)
W=1
1
2
B/
3
0.001
(0.007)
0.0001
(0.0007)
Figure 11.26
Over-pressure as a
function of scaled distance for bench
blasting (Ladegaard-Pedersen and
Dally, 1975).
1
(0.4)
10
(4)
100
(40)
1000
(400)
10 000
(4000)
Scaled distance R/
3
W—ft/lb
1/3
(m/kg)
1/3
is 1.8 m (see equation (11.1)). The adjusted
burden to account for the rock condition is
2.3 m, using equation (11.4) with
k
ψ
=
gravity of 1.3 and a diameter of 78 mm, the
weight of explosive per hole is 31.7 kg.
1.18
(c)
The volume of rock to be broken per hole is
38.6 m
3
, for a bench height of 6 m, a burden
of 2.3 m and a spacing of 2.8 m.
The powder factor is 0.8 kg/m
3
. With ref-
erence to Figure 11.8, the average boulder
size of the blasted rock will be about 0.4 m,
which can be readily loaded with a front-end
loader.
=
and
k
s
1.1.
The explosive diameter, calculated from
equation (11.2), is 78 mm.
The spacing between holes,
calculated
from equation (11.5), is 2.8 m.
(b)
The depth of subgrade drilling is 0.7 m,
based on a subgrade depth equal to 0.3 of
the burden.
The length of the stemming is 1.6 m, based
on a stemming length equal to 0.7 of the
burden.
The length of the explosive column is
5.1 m, based on a bench height of 6 m, a sub-
grade depth of 0.7 m and a stemming length
of 1.6 m. For this explosive length, a specific
11.7 Example Problem 11.2: controlled
blasting design
Statement
A 6 m high slope has been previously excavated
for a highway by blasting, and it is required that
