What is pre-cracking? What is the difference between pre-cracking and buffering?

Open-pit mine pre-splitting blasting is to drill a row of dense pre-splitting holes on the slope boundary, and blast before the main blasthole blasting. When the pre-cracking hole is blasted, it develops into a pre-crack along the hole connecting line. Pre-cracking blasting can significantly reduce the damage caused by blasting to the slope and the amount of cleaning work.

Pre-cracking blasting construction is shown in Figure 1.

Figure 1 Schematic diagram of pre-cracking

1- auxiliary hole; 2-pre-cracking hole; 3-pre-cracking line; 4-buffering hole; S ₁ -2.5 to 3 m; S ₂ -1 to 2 m

Pay attention to the following points when pre-cracking blasting:

1. Strictly according to the design hole position construction, in the open pit excavation project, the displacement deviation of the blasthole before and after should not exceed 20~30cm.

2. When using the uncoupled charge structure, the drug pack should be placed in the center of the blasthole as much as possible, and the dose at the bottom of the blasthole should be increased by 1 to 3 times.

Third, the blasthole is generally not deep, and the unfilled portion of the orifice is 15% to 30% of the depth of the hole.

4. The pre-split hole shall be detonated in advance or advanced 50 to 100 ms adjacent to the main blasthole.

5. Pre-cracking holes should generally be detonated at the same time, but in order to reduce the seismic wave effect of pre-cracking blasting, it can also be detonated in stages.

Buffer blasting is the ratio of the amount of the dose from the front row to the back row, so that the vibration intensity behind the blast zone depends on the explosion of the last row of holes. The characteristics of buffer blasting are: the row spacing from the previous row to the undischarged hole, the ultra-deep gradual decrease, and the un-arranged holes in the boundary line of the slope are dense. The amount of charge is gradually reduced, and the distribution is more uniform, which reduces the blasting vibration. Both buffer blasting and pre-cracking blasting are called shock blasting. The difference between the two is that the pre-crack blasting detonates before the main blast hole, and a crack is pre-expanded between the main blast and the protected rock mass, and the buffer blasting is simultaneously detonated with the main blast hole, due to the charge amount. Reduced, reduced blasting vibration damage.

Barbell bar a long bar which is used in barbell, one kind of exercise tools used in weight training, bodybuilding, weightlifting and powerlifting. The barbell bar length ranges from 1200mm to 2400mm. The barbell bar diameter ranges from 25mm to 50mm. The barbell bar can be used for both competitive sports such as powerlifting, Olympic weight lifting, CrossFit. and other exercises such as bicep curl, bench press, overhead press, deadlift, and squat etc.

Among the various barbell bars, 20kg barbell bar is the most popular and standard barbell bars.