Tunnel Construction MCQ with answer and solution

Concept

Rock tunneling involves methods suited for self-supporting or blasted strata (Full face, Heading & bench, Drift methods), whereas forepoling is an auxiliary support method for non-cohesive, soft, or running soils.

Step-by-step solution

1. Identify the methods utilized for tunneling in rock: Full face method, Heading and bench method, Drift method, and Perimeter blasting method. 2. Identify methods utilized for tunneling in soft or loose ground: Forepoling method, Needle beam method, Liner plates method, Shield tunneling, and Compressed air method. 3. Note that 'Forepoling method' relies on driving wooden/steel planks (spiles/poles) into loose, soft, or running ground ahead of the excavation face. 4. Therefore, Forepoling is NOT used while tunneling in rock.

Explanation

Forepoling is an ancient method of tunneling specifically employed in running ground, soft soil, or loose water-bearing strata rather than solid rock. In rock tunneling, methods like Full Face, Heading and Bench, and Drift methods are standard drilling and blasting approaches. Therefore, the forepoling method is NOT used while tunneling in sound or hard rock.

Why the other options are wrong

A: Drift method is widely used in rock tunneling where a small pilot tunnel (drift) is driven first to relieve internal rock pressure and provide ventilation. B: Full face method is the most common rock tunneling method for small to medium cross-sections in sound rock. D: Heading and bench method is a classic rock tunneling technique where the top heading is driven first followed by the bench excavation.

Shortcut

Remember: 'Drift', 'Bench', and 'Full face' are rock methods; 'Forepoling', 'Needle beam', and 'Shield' are soft ground methods.

Common mistake

Candidates often confuse the Drift method with soft ground tunneling because a small drift is excavated first, but it is actually a prominent rock tunneling method used in large or poor rock sections.