Ballast maintenance terminology: In routine track upkeep, “boxing of ballast” is carried out primarily at which location relative to the rails and sleepers?

Introduction / Context:
Track maintenance includes operations like packing, tamping, and boxing of ballast. “Boxing” refers to shaping, trimming, and dressing the ballast profile so that the shoulders at the rail seats and the cribs between sleepers are properly formed to provide lateral stability and correct drainage.

Given Data / Assumptions:

• Ballasted track with sleepers and rails in standard configuration.
• Objective is to maintain profile and resistance against track movement.

Concept / Approach:
Ballast must be dressed to a defined cross-section. At the rails (near rail seats and shoulders), correct boxing prevents rail roll, enhances lateral resistance, and protects sleeper ends. Although ballast also exists between sleepers and rails, “boxing” in common usage highlights shaping at the rails and shoulders to maintain the “box” profile.

Step-by-Step Solution:

Verification / Alternative check:
Maintenance manuals depict the boxed ballast section with distinct shoulders adjacent to rails, indicating where shaping is critical for stability.

Why Other Options Are Wrong:

• Under rails: Packing/tamping occurs beneath sleepers; “boxing” refers more to surface shaping.
• In between two rails only / between sleepers only: Too narrow a description; boxing concerns the full ballast profile at rails and cribs.
• Below subgrade: Not a maintenance activity termed boxing.

Common Pitfalls:

• Equating boxing with tamping under sleepers; they are distinct operations.
• Ignoring the importance of shoulder height for lateral resistance and drainage.

Final Answer:
at the rails (forming and dressing ballast shoulders/cribs)