During the detailed survey of a hill road alignment, which operation should be carried out first to establish reliable control for subsequent measurements?

Introduction / Context:
Detailed surveys for hill roads require robust horizontal and vertical control because steep terrain amplifies errors in gradients, cross-slopes, and earthwork estimates. Establishing benchmarks is foundational for all subsequent operations in the survey workflow.

Given Data / Assumptions:

• Project: hill road detailed survey after preliminary alignment.
• Need: stable vertical control (reduced levels) and reference points.
• Equipment: precise levels/total stations for transfer of elevations.

Concept / Approach:
Bench Marks (BMs) provide permanent elevation references. With known BMs, surveyors can correctly set grades, profile the centerline, and layout cross-sections. Without them, longitudinal levels and curve setting would be unreliable, risking design inaccuracies and construction disputes.

Step-by-Step Solution:
Establish and verify Bench Marks tied to a datum.Run control leveling to transfer RLs along the proposed corridor.Proceed to take longitudinal/cross sections, then refine horizontal/vertical curves.Carry out hydrological/soil surveys and stake out after control is secure.

Verification / Alternative check:
Standard survey practice places control establishment (BMs and traverse) at the start so that all subsequent measurements are consistent and repeatable.

Why Other Options Are Wrong:

• Hydrology/soils: rely on correct levels/locations from control.
• Alignment adjustments and staking: require accurate control first.
• Profiles/sections: cannot be trusted without BMs.

Common Pitfalls:

• Using temporary, unstable marks in steep terrain.
• Skipping BM verification after landslides or heavy rainfall.

Final Answer:
Fixation of Bench Marks