Which of the following advantages are correct regarding poly-centric shape tunnel? 1. It can be conveniently used for road and railway traffic 2. The number of centres and lengths of radii cannot be fixed 3. It can resist external and internal pressure due to its arch action
- A1 and 2 only
- B1 and 3 onlyCorrect
- C2 and 3 only
- D1, 2 and 3
Solution
Concept
Poly-centric Tunnel Properties
Formula
N/A
Step-by-step solution
1. Review the given statements regarding poly-centric shape tunnels. 2. Verify that statements 1 and 3 are correct, while statement 2 is incorrect because the number of centers and radii lengths can be fixed. 3. Select Option (b) as the correct choice.
Explanation
Option B (1 and 3 only) is correct because a poly-centric tunnel has a flat base that makes it suitable for road and railway traffic, and its arch-like shape allows it to resist both internal and external pressures effectively. Statement 2 is incorrect because the number of centers and radius lengths can be fixed by the engineer based on site conditions.
Shortcut
To remember key properties of Poly-centric Tunnels, use the memory rule "Flat Floor, Fixed Arch": - Flat Floor for Traffic: Suitable for both road and railway traffic. - Fixed Geometry: The number of centers and radii lengths are explicitly FIXED by design (not variable/unfixed). - Strong Arch: Resists internal and external pressures through arch action.
Common mistake
A common mistake is selecting option D by assuming statement 2 is correct. Students often misinterpret statement 2, thinking poly-centric shapes have completely variable geometry, whereas the number of centers and radii lengths are explicitly fixed by the engineer during design. Another common error is choosing option C by overlooking statement 1, failing to realize that the flat base of a poly-centric tunnel makes it well-suited for road and rail traffic.
Correct answer: B) 1 and 3 only