Track ballast practice: Coal ash (cinder) is used during the initial stage of new railway construction primarily with which type of sleepers?

Introduction / Context:
Ballast provides load distribution, drainage, and stability to the permanent way. While high-quality crushed stone is preferred, historically some projects used coal ash (cinders) in the early stages. This question tests practical knowledge of which sleeper types can tolerate such inferior ballast during initial construction or temporary works.

Given Data / Assumptions:

• Material: Coal ash (cinder), relatively light and less durable than stone ballast.
• Context: Initial stages of construction, temporary packing before final ballasting.
• Sleeper types considered: wooden, steel, cast iron, and others.

Concept / Approach:
Wooden sleepers possess a broad bearing area and some resilience, allowing them to perform more acceptably with lower-grade ballast for short periods. Steel sleepers require better ballast interlock to maintain gauge and resist corrosion; cast iron pot sleepers also need stable support to prevent concentrated stresses. Thus, cinders are historically associated with temporary packing under wooden sleepers, particularly in sidings or low-speed stretches during construction.

Step-by-Step Solution:

Verification / Alternative check:
Conventional railway engineering notes list cinder as an inferior ballast acceptable mainly for temporary works and most suited under wooden sleepers; it is specifically discouraged beneath steel sleepers due to corrosion and inadequate interlock.

Why Other Options Are Wrong:

• Steel sleepers: Require high-quality, angular stone; cinder promotes corrosion and poor lateral restraint.
• Cast iron sleepers: Concentrated bearing can crush cinder, leading to settlement and gauge issues.
• Prestressed concrete sleepers: Modern PSC sleepers demand strong, well-graded stone ballast only.
• None of these: Incorrect because wooden sleepers are a recognized (temporary) use case.

Common Pitfalls:

• Assuming cinder ballast is acceptable for mainline permanent use—it is not.
• Overlooking drainage; cinder retains moisture and fouls quickly.

Final Answer:
Wooden sleepers