Which one of the following methods is achieved by drilling a drift through the tunnel from portal to portal ?
- ABlow-in method
- BExhaust method
- CBlow-out method
- DNatural methodCorrect
Solution
Concept
Natural ventilation of tunnels
Step-by-step solution
1. Natural ventilation depends on air movement caused by temperature or pressure difference between the two portals. 2. It is achieved by driving a drift through the full length so that air can pass from portal to portal.
Explanation
Mechanical methods (blowing in, exhaust and blowing out) use fans, while the natural method relies on a through opening.
Why the other options are wrong
Blow-in, exhaust and blow-out are the forced ventilation methods that use fans and ducts.
Shortcut
Through drift = natural ventilation.
Correct answer: D) Natural method