What is a membrane polder construction?
A membrane polder construction is an underground excavation pit or basement in which a waterproof plastic membrane (usually HDPE) is applied around the structure as a water barrier, instead of a fully watertight concrete tank. This method, also called a membrane polder or polder construction, makes it possible to build deep below the groundwater level by keeping groundwater out with the membrane.
Construction
In a membrane polder construction, an excavation pit is first dug, after which a continuous membrane sheet (HDPE) is laid over the base and up the walls and welded watertight. The actual concrete structure is then built against the membrane. The membrane forms a closed “tub” around the basement:
- Base membrane beneath the basement floor.
- Wall membrane along the retaining walls, generally carried up above the groundwater level.
- Welded seams that must be fully watertight and verifiable.
Application
The membrane polder construction is used for:
- deep basements and souterrains below the groundwater level;
- underground car parks in urban, wet locations;
- situations where a traditional watertight concrete tank is technically or economically unfavourable.
Considerations
The membrane must withstand the water pressure and must not be damaged during concrete pouring. A leak detection system is often installed between membrane and concrete, so that any leakage can be located and repaired. The pressure distribution of the groundwater on the membrane and the upward water pressure beneath the floor govern the design.
Related terms
- Membrane polder
- Excavation pit
- Watertight concrete tank
- Groundwater level
- Leak detection
- Uplift pressure
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