In sewer design for buried conduits: A sewer running partially full and surrounded by compacted backfill can fail in compression due to which combined actions?

Introduction / Context:
Sewers are often laid below ground level and are usually designed to carry flow partially full. Even though internal water pressure is low, the pipe can fail structurally due to external compressive effects. Understanding the sources of compressive loading helps in choosing pipe class, bedding, and backfill specifications for long-term performance.

Given Data / Assumptions:

• Buried circular sewer, running partially full.
• Pipe is surrounded by backfill placed to finished ground level.
• Potential additional live loads from vehicles or construction traffic may act at ground surface.

Concept / Approach:
Compression in buried pipes arises from dead loads (pipe self-weight and soil prism above the pipe) and live loads (traffic). The soil-structure interaction transfers loads to the pipe barrel. If bedding support is inadequate or pipe class is insufficient, longitudinal or ring compression may exceed limits and cause cracking or buckling in brittle materials.

Step-by-Step Solution:
Identify dead load components: pipe weight + backfill prism weight.Identify live load component: wheel loads creating additional stress through distribution in the soil cover.Recognize that combined loading increases compressive stress in the pipe wall.Conclude that all listed actions contribute to compression and potential failure.

Verification / Alternative check:
Buried pipe design methods (for example trench or embankment formulas) explicitly include soil load and live load terms in the ring compression check, confirming the combined effect.

Why Other Options Are Wrong:
Self-weight only: ignores dominant soil prism weight.Backfill only: neglects pipe weight and traffic loads.Traffic only: not the only contributor; dead loads are always present.

Common Pitfalls:

• Assuming partial flow means negligible structural load.
• Ignoring compaction-induced stresses during construction.
• Underestimating surface traffic effects for shallow cover depths.

Final Answer:
All of the above