Pipe Loading
The load cases a buried sewer is designed for.
Design guidanceLoad models follow the design standard; the surface load class is a project requirement.
Buried pipes are loaded by the soil above them, by surface traffic, by groundwater, and by construction activity. The governing case is not always the deepest cover.
Shallow cover carries the highest surface load concentration, while deep cover carries the most soil load. For flexible pipes, construction loads during compaction can exceed both.
Reference table
| Load case | Typically governs |
|---|---|
| Shallow cover with heavy traffic | Surface load at the crown |
| Deep cover | Soil load, and installation practicality |
| Groundwater above the pipe | Wall pressure and flotation checks |
| Compaction adjacent to the pipe | Flexible pipe deflection and damage |
Key design considerations
- Soil prism load, influenced by trench width, installation condition and soil unit weight.
- Surface load class, and how the load distributes through the fill with depth.
- Hydrostatic load where groundwater is above the pipe, including the empty-pipe condition.
- Construction loads, including compaction plant working close to the pipe.
- Load combination and factors required by the design standard.
- Concentrated loads from structures, footings or temporary works above the pipe.
Design checks
- Surface load class appropriate to present and future use of the surface.
- Groundwater level adopted is defensible, not just the day of investigation.
- Empty-pipe condition checked where groundwater is present.
Standards and authority references
- AS/NZS 2566.1 Buried flexible pipelines — Structural design
- AS/NZS 3725 Design for installation of buried concrete pipes
- Road authority vehicle loading requirements where adopted
Confirm the current edition, amendment and any local supplement before applying any of the above.
Limitations and assumptions
- Load models are idealisations; the design standard's assumptions must be followed consistently.
- Future surface loading can be higher than the current use.
This reference is general engineering information. Confirm requirements against WSA 02, the current Australian Standards and the local water authority's supplement before use in design, and obtain project-specific advice for the conditions at hand.