What is a voorhei?
A voorhei, also called a proost, is a wide, pointed steel spike that is temporarily driven into the ground to clear the way for a pile. Working with a voorhei is called voorheien (pre-driving).
Why pre-drive?
Concrete piles can break or be damaged if they hit a hard obstacle during driving. Think of:
- rubble and old foundation remains in the upper soil layers;
- old timber or concrete piles from earlier buildings;
- hardened layers, such as old road or quay structures.
The voorhei is driven at the position of the new pile to a depth of a few metres (often 3 to 4 metres) to break such obstacles or push them aside. The voorhei is then pulled out again and the concrete pile can be driven in the same spot.
How it works in practice
- Often several pile positions are pre-driven one after the other before the voorhei is swapped for the piles. This keeps the daily output of the piling rig up.
- The piling plan and setting out must be exactly right: the pile has to go into the hole made by the voorhei.
- With a lot of rubble or heavy obstacles, excavation or pre-boring is sometimes a better solution. The foundation adviser decides this on the basis of the soil investigation.
Applications
Pre-driving is mainly used for building in inner cities and on former building or industrial sites, where the ground often contains remains of earlier buildings. Good preliminary research into the history of the site prevents surprises, such as broken piles that have to be replaced or supplemented with extra piles.
Related terms
- Pile
- Piling rig
- Foundation
- Pruikheien (driving piles with a damaged head)
- Foundation repair
Want to learn more about construction terms? Visit our knowledge base at fredsdiyplans.com.