- Rock usually takes "60 ms(milli-second )" to move around "1 m".
- A blasting is said to healthy when it is free from fly rocks, with minimum vibration and boulders up to 1 %.
- Drilling and blasting cost should be within 22 % of the contract price.
- Minimum stemming of 3.5 meter should always be maintained.
- Efforts should be made to complete the blasting within 800 ms.
- Range of burden/spacing should be between 0.5 and 1.0.
- For optimum breakage, bench height/burden should be around 2.5.
- For satisfactory throw, bench height/burden should be greater than 2.5.
- Bench height should be between 10 and 12 m.
- If the stemming height is 1.2 to 1.5 times the burden then fly-rock can easily be controlled.
- bold parts are thumb rules.
Rock type(based on RMR)
|
Burden(in meter)(B)
|
Spacing(in meter)
|
Stemming(in meter)
|
Very poor
|
51 X D*
|
1.45 X B
|
1 X B
|
Poor
|
44 X D
|
1.34 X B
|
0.95 X B
|
Medium
|
37 X D
|
1.25 X B
|
0.95 X B
|
High
|
29 X D
|
1.19 X B
|
1.1 X B
|
Very high
|
23 X D
|
1.14 X B
|
1.1 X B
|
- D: diameter of hole in mm (100,160,…..)
