Question

Information for a drilling operation in an overburden mine is given: Volume of rock blasted per round = \(3.2 \times 10^5\ \text{m}^3\)
Number of blast holes = 100
Drill hole diameter \(D = 200\ \text{mm} = 0.2\ \text{m}\)
Length of subgrade drilling = \(8D = 1.6\ \text{m}\)
Stemming length = \(25D = 5\ \text{m}\)
Bench height = 30 m
Powder factor = \(3.2\ \text{m}^3/\text{kg}\) Find the explosive per unit charge length (kg/m), rounded to two decimals).

Hint:

Explosive per meter = (Total kg of explosive per hole) / (chargeable length). Stemming and subgrade drilling must be accounted for.

Answer 1

Correct Answer: 36

Step 1: Amount of explosive required per round. \[ W_{\text{round}} = \frac{\text{Rock volume}}{\text{Powder factor}} = \frac{3.2 \times 10^5}{3.2} = 1.0 \times 10^5\ \text{kg} \] Step 2: Explosive per hole. \[ W_{\text{hole}} = \frac{1.0 \times 10^5}{100} = 1000\ \text{kg/hole} \] Step 3: Chargeable length (explosive column length). Total hole depth: \[ L_h = 30 + 1.6 = 31.6\ \text{m} \] Subtract stemming: \[ L_c = 31.6 - 5 = 26.6\ \text{m} \] Step 4: Explosive per unit length. \[ \frac{W_{\text{hole}}}{L_c} = \frac{1000}{26.6} = 37.59398\ \text{kg/m} \] Rounded to two decimals: \[ \boxed{37.59\ \text{kg/m}} \]