How to arrange the blasthole in the shallow hole collapse? How to choose the blasting parameters?

The phenomenon of shallow-hole collapse blasting in underground is characterized by having more than two free faces, and the blasting area and blasting amount are both large. The requirements for collapse blasting are: safety of blasting operation; large amount of collapsing per metre of blasthole, high recovery intensity; small size, small secondary crushing; low ore depletion rate and loss rate;

The blasthole arrangement has two types of upward and horizontal eyes (see Fig. 1), and the upper eye is more widely used. The arrangement is two-way and staggered, as shown in Figure 2 (É‘), (b), (c). When staggered, the blasting energy is evenly distributed in the ore body, and the blasting block is more uniform and more used. When the sampling width is narrow, the staggering effect is better. The parallel arrangement is often used for ore bodies in which the ore and surrounding rock are not easily separated or the boundary is not obvious.

Figure 1 blasthole direction

Figure 2 Arrangement of blastholes in mine road collapse

(É‘) parallel arrangement; (b) wide staggered arrangement; (c) narrowly staggered

Selection of gun-breaking parameters: Due to the large-scale use of shallow-eye collapse in China, the diameter of the shallow-eye collapse is 32mm, and the corresponding diameter of the hole. It is 38 to 42 mm. Therefore, this specification is now used more. Non-ferrous metal mines but also the use of small diameter 25 ~ 28mm explosives to blow up, and made a more significant effect. At this stage, township enterprises or mining thin veins, especially for the mining of rare metals and precious metal deposits, use small diameter blastholes for better blasting.

The depth of the blasthole, when the ore body is thin and irregular in shape, and the ore is not stable, it should take a small value to control the mining amplitude and reduce the loss and depletion of the ore. The common depth of the eye is 1.5 to 2.5 m, sometimes Up to 3 ~ 4m.

The minimum resistance line, when the mine collapses, the blasthole row spacing is usually equal to the minimum resistance line W, which can be obtained by:

W=(25-30)d

In the formula:

D-gun hole diameter, mm.

The blasthole spacing refers to the distance between adjacent blastholes in the same row. Expressed in É‘.

É‘=(1.0-1.5)W

In the formula:

W-minimum resistance line, mm.

When W is too large, it will reduce the quality of the crushing, and the bulk will be large; on the contrary, if it is too small, the ore will be excessively crushed, which will increase the cost of rock drilling, waste blasting equipment , and bring the oxidative and easy-bonded ore shipment work. difficult.

Explosive unit consumption is related to ore properties, explosive properties, blasthole diameter and depth, and width of the mining.

The common consumption of common underground blasting explosives is as follows:

Rock solidity factor f <8 8～10 10～15

Explosive unit consumption (kg/m ³ ) 0.26~1.0 1.0～1.6 1.6～2.6

The total charge Q of the blasting in the stope can be calculated by the following formula:

Q=qA·B·L

In the formula:

Q-explosive unit consumption, kg/m ³ ;

A-width of the mining, m;

B- total length of a collapse, m;

L-average blasthole depth, m.