Deep-hole blasting in open pit mines, in order to facilitate calculation and help to reduce the roots, generally use the chassis resistance line without the minimum resistance line, that is, the minimum horizontal distance from the center of the blasthole to the bottom line of the step slope. If the chassis resistance line is too large, the residual base will increase and the back impulse will increase. The chassis resistance line is too small, which not only increases the perforation workload, wastes explosives, but also makes the puncher too close to the top line of the step slope. Safety.
The chassis resistance line is determined as follows:
First, consider the empirical formula of the aperture and other factors:
W d = (25 ~ 45) d
In the formula:
W d - chassis resistance line, m;
D-gun hole diameter, m.
Second, according to the safe working conditions of the piercing equipment:
W d ≥H(ctgα-ctgβ)+C
In the formula:
H-step height, m;
--step slope angle, °;
Β-gun hole inclination angle, vertical hole is 90°;
The safety distance from the center of the C-front hole to the top line of the step slope is generally 2 to 3 m.
Third, according to the height of the step:
W d = (0.6 ~ 0.9) H
4. Calculate according to the charging conditions of each blasthole:
In the formula:
â–³-charge density;
Τ-charge coefficient;
L-deep hole length;
M-burst density factor;
q-Explosive unit consumption.
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