Placement rules recap: A manhole is generally provided at each bend, junction, change of gradient, or change of sewer diameter. Which option best summarizes this practice?
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AAt each bend
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BAt each junction
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CAt each change of gradient
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DAt each change of sewer diameter
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EAll the above
Answer
Correct Answer: All the above
Explanation
Introduction / Context:Manhole spacing and placement rules are foundational to sewer design. They ensure safe access where flow conditions and geometry are most complex, reducing maintenance time and preventing chronic blockages at hydraulic transitions and network nodes.
Given Data / Assumptions:
- Gravity sewer network with multiple junctions and geometry changes.
- Need for access for inspection and cleaning equipment.
- Standard design practices are followed.
Concept / Approach:
Provide manholes at bends (direction changes), junctions (network connections), changes in gradient (invert slope), and changes in pipe diameter. On long uniform reaches, additional manholes are spaced at practical intervals to maintain access, with spacing depending on pipe size and local codes.
Step-by-Step Solution:
List all geometry or network change points.Assign manholes at each to accommodate cleaning and inspection tools.Verify additional spacing manholes as per standards (e.g., 30–100 m).Ensure safe benching and channeling inside manholes for smooth flow.Verification / Alternative check:
Operation and maintenance guidelines from utilities confirm lower blockage incidence when manholes are provided at these points.
Why Other Options Are Wrong:
Choosing only one location ignores the other critical points requiring access; comprehensive practice is captured by “All the above”.
Common Pitfalls:
Omitting manholes at diameter transitions; excessive spacing on small sewers; poor alignment causing excessive headloss through manholes.
Final Answer:
All the above