Regarding survey and control for setting out an inclined tunnel, identify the statement that is NOT correct about alignment and level transfer practices.

Introduction / Context:Setting out an inclined tunnel requires robust surveying controls to ensure the correct line and level are maintained as excavation progresses. Permanent reference points, precise levelling, and protected control marks are essential, especially because resection and transfer must be repeated over long distances underground.

Given Data / Assumptions:

• Tunnel is inclined and may be driven from different ends or headings.
• Control involves plan alignment and vertical level transfer.
• Standard underground survey practices are followed.

Concept / Approach:

Accurate levelling is done with survey instruments (levels/total stations) and permanent benchmarks; using a simple tape to ‘‘mark level’’ is not acceptable for precision. Reference points are spaced periodically and often placed in the roof to avoid damage, providing a reliable framework to maintain alignment and grade.

Step-by-Step Solution:

Verification / Alternative check:

Modern practice commonly supplements traditional methods with lasers and prisms, but still relies on accurate benchmarks and instrument levelling; tapes are unsuitable for precision level control.

Why Other Options Are Wrong:

• Reference points at intervals: Correct, provides consistent control.
• Alignment from apex/portals: Correct way to define direction.
• Reference points on the roof: Correct, protects control marks.
• None the above: Incorrect, since one statement is indeed not correct.

Common Pitfalls:

• Allowing control points to be damaged or covered, leading to cumulative alignment errors.
• Relying on rough methods (like tapes) for level transfer, which lack required accuracy.

Final Answer:

The level of the invert at the heading is marked by a tape.