Pipeline accessibility: manholes along raw-water/clear-water mains from the source to a city are generally provided at about 500 m intervals in which type(s) of pipe?

Introduction / Context:
Access structures enable inspection, cleaning, and maintenance of large conveyance pipelines. The need and feasibility of providing manholes depend on pipe material, diameter, and structural considerations.

Given Data / Assumptions:

• Manholes are placed at intervals of approximately 500 m along large mains.
• We must identify the pipe type where such manholes are typically provided.

Concept / Approach:
Large-diameter R.C.C. (including hume) pipelines commonly incorporate manhole openings because the wall thickness and reinforcement can be detailed around access frames while maintaining integrity. Small/medium steel mains generally use inline fittings (air/scour) and pigging, with fewer full manhole entries due to thin walls and pressure considerations.

Step-by-Step Solution:
Recognize that R.C.C. mains are often large and buried—access is via manholes. Steel mains typically rely on appurtenances rather than frequent manholes. Select “R.C.C. pipes” as the standard case for 500 m manhole spacing.

Verification / Alternative check:
Practice notes specify manholes on large concrete conduits, while steel lines favor tapping points and inspection ports rather than full manhole entries at such close spacing.

Why Other Options Are Wrong:

• Steel pipes: Less common for manholes; structural and practical constraints.
• Hume steel pipes (R.C.C. with steel): Often treated under R.C.C. practice; if narrowly interpreted, the standard textbook answer highlights R.C.C. pipes.
• All the above: Overgeneralizes; not typical across all materials.

Common Pitfalls:

• Assuming every material supports frequent manholes irrespective of diameter and pressure class.

Final Answer:
R.C.C. pipes.