Groundwater Considerations
Uplift, dewatering, infiltration and chemical attack.
Groundwater affects a sewer at every stage: it loads the pipe and structures, it can float an empty pipeline during construction, it infiltrates the network in service, and its chemistry can attack concrete and metal.
The level used for design should be the highest credible level, based on investigation and flood data, not only the level recorded during one site visit.
Key design considerations
- Design groundwater level: highest recorded or design flood level, whichever is higher.
- Uplift on maintenance holes and other structures, and flotation of empty pipes.
- Dewatering during construction, including settlement risk to adjacent assets.
- Infiltration allowance in the design flow, and its relationship to asset condition.
- Sulfate and chloride content of soil and groundwater, which governs concrete durability.
- Buoyancy of lightweight pipe in a flooded trench, before backfill is complete.
Design checks
- Design groundwater level stated in the design basis.
- Flotation check at the construction stage, with the pipe empty.
- Durability classification supported by test results.
Standards and authority references
- Geotechnical and groundwater investigation
- Authority durability and infiltration requirements
- Concrete durability provisions of AS 3600 where applicable
Confirm the current edition, amendment and any local supplement before applying any of the above.
Limitations and assumptions
- Groundwater levels vary seasonally and with nearby extraction; a single investigation may understate the risk.
Related calculators
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.