Underground sewer pipes installed in trenches are generally subjected predominantly to which kind of internal action from surrounding loads?

Introduction / Context:
Buried sewers behave as rings under earth load and superimposed surface loads. Understanding the predominant internal action informs material selection and wall thickness.

Given Data / Assumptions:

• Pipe laid in a trench with soil backfill.
• Uniform soil support around the pipe.
• Typical municipal burial depths.

Concept / Approach:
Ring compression is the dominant internal action in circular buried conduits due to vertical earth load and lateral soil reaction. Proper bedding distributes load and reduces bending.

Step-by-Step Solution:
Step 1: Model pipe as a ring under vertical load; lateral soil provides passive resistance.Step 2: The ring develops circumferential compressive thrust (hoop compression).Step 3: Bending is secondary when bedding and side support are adequate.

Verification / Alternative check:
Design equations for vitrified clay, concrete, and plastic pipes use crushing strength (compressive) ratings and bedding factors, confirming compression is primary.

Why Other Options Are Wrong:

• Tension: Pipes are poor in tension and not the primary demand in buried state.
• Bending primary: Can occur with poor support, but not the general design assumption.
• Shear/Torsion: Not governing for uniformly supported buried rings.

Common Pitfalls:
Ignoring bedding quality and lateral support, which can raise bending stresses beyond assumptions.

Final Answer:
Compressive force