The event in rock tunnelling are given below 1. Making tunnel profile 2. Loading explosive and blasting 3. Checking misfire 4. Mucking 5. Removing foul gases 6. Setting up and drilling 7. Guniting Choose the correct sequence:
- A1, 6, 2, 5, 4, 3, 7
- B1, 6, 2, 5, 3, 4, 7Correct
- C1, 6, 5, 3, 4, 2, 7
- D1, 2, 6, 3, 5, 4, 7
Solution
Concept
Rock Tunnelling Operations
Formula
N/A
Step-by-step solution
1. Analyze the required sequence for rock tunneling: Mark profile (1), Set up/drill (6), Load/blast (2). 2. Follow post-blast safety and clearing steps: Remove foul gases (5), Check misfires (3), Muck debris (4), and Apply guniting (7). 3. Match the combined order 1, 6, 2, 5, 3, 4, 7 with Option B.
Explanation
In rock tunneling using drill-and-blast, operations follow a logical safety and construction sequence:1. Making tunnel profile: Mark the tunnel shape and drill holes on the rock face. 2. Setting up and drilling: Position equipment and drill holes for explosives. 3. Loading explosive and blasting: Load charges into holes and detonate. 4. Removing foul gases: Ventilate the area to clear toxic smoke and fumes. 5. Checking misfire: Inspect the blast site to ensure all explosives went off safely. 6. Mucking: Clear and remove the blasted rock debris. 7. Guniting: Apply shotcrete/concrete lining to support and stabilize the freshly exposed tunnel surface.
Shortcut
To remember the sequence of rock tunneling operations, use the mnemonic "P-D-B-G-C-M-G" (Please Do Blast Gases, Check Muck & Gunite): - P (1): Profile - Mark the tunnel profile - D (6): Drill - Set up and drill holes - B (2): Blast - Load explosives and blast - G (5): Gases - Remove foul gases/fumes - C (3): Check - Check for misfires before entering - M (4): Muck - Clear and remove mucked debris - G (7): Gunite - Apply guniting/shotcrete support
Common mistake
A common mistake is selecting Option A by placing mucking (4) before checking for misfires (3). Before clearing debris (mucking), the site must be inspected for misfires to prevent accidental explosions from unexploded charges. Another frequent error is selecting Option D by reversing the order of drilling (6) and loading explosives (2).
Correct answer: B) 1, 6, 2, 5, 3, 4, 7