Ballast specification near pointwork: What is the maximum nominal ballast size permitted around points and crossings for reliable tamping and smooth wheel guidance?

Introduction / Context:
Points and crossings require finer control of alignment and level. Large ballast particles can obstruct switch movement and prevent proper packing in confined spaces near stretcher bars and heel joints. Hence a smaller maximum size is specified.

Given Data / Assumptions:

• Standard Indian practice near turnouts.
• Need for unobstructed switch operation and effective tamping.

Concept / Approach:
Reducing maximum ballast size improves interlock and packing in tight areas, enhancing stability and switch operation while minimizing the chance of ballast fouling moving parts.

Step-by-Step Solution:
Recognize special operational and geometric constraints at pointwork.Adopt finer grading with nominal maximum size 25 mm.Ensure cleanliness and adequate depth to maintain drainage and stiffness.

Verification / Alternative check:
Turnout maintenance guides specify smaller stone sizes around switch and crossing zones for smooth operation and reduced damage.

Why Other Options Are Wrong:

• 50, 40, 30 mm: too large near moving parts and tight clearances.
• 20 mm: possible but not the standard upper limit; 25 mm is widely prescribed.

Common Pitfalls:

• Using mainline ballast size (40–50 mm) in switch zones, causing obstruction and poor packing.

Final Answer:
25 mm.