Ultra-deep refers to the depth of the blasthole beyond the height of the step. The purpose of ultra-deep is to reduce the position of the center of the charge to effectively overcome the resistance of the chassis resistance line to eliminate the root. Too small and ultra-deep will leave a base after blasting. Excessive ultra-deep will increase the amount of perforation, waste explosives and equipment, and destroy the next stage after blasting, making it difficult to perforate the next step.
Shallow hole blasting ultra deep h:
h=(0.1～0.2)H
In the formula:
H-step height, m.
Deep hole blasting is commonly used to determine the formula for ultra deep:
In the formula:
Q 1 - The amount of charge per metre of the blasthole, kg/m.
When tilted holes are used, the calculated value is reduced by 20%.
Alternatively, the chassis can be used to determine the ultra-deep values ​​against the line W d and the aperture d:
h=(0.15～0.3)W d
Or h=(10~15)d
The parameters of ultra-deep calculation should be selected with reference to the rock's firmness coefficient f value. The f-value is high. When calculating, the coefficient takes a large value, the f-value is small, and the calculation takes a small value. In the case of multi-row hole blasting, the depth of each row of blastholes after the second row may be large, and when the rock of the stepped chassis is soft, it may not be ultra-deep.
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