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  • The concrete or reinforced concrete piles are formed in situ. A self propelled rig is used.
  • During the installation of De Waal piles there is no soil subsidence or mining.
  • The concrete piles may contain a reinforcement cage along their entire lengths or a prestressed element
  • The speed of installation compares favourably with the speeds achieved with driven piles.

A special three section auger causes lateral displacement of the soil during installation, further compressing the hole waals.

The lower section comprises of a thick waaled steel tube with welded auger flights of uniform pitch. The exterior diameter of the flights defines the pile diameter.

The connecting element is very short and comprises of two sections on a common axis with the flights in opposite directions. The diameter is not constant and at its widest achieves the size of the pile diameter which makes it impossible for the soil on the flights to be excavated above the auger during drilling. This causes an empty cavity to form around the top of the auger. The reversed flights on the upper part of the connecting section mean that during extraction of the auger (rotation in the same direction as during drilling) a further displacement and compaction of the waals occur without mining the soil.

The upper section of the auger is a straight, 10 to 20 m tube of the same size as the tube at the bottom. For installing 360 to 510 mm diameter piles, a 273/219 mm tube is used.

Before the auger begins to drill a sacrificial shoe is placed in its tip. The sacrificial shoe acts as a plug for the hollow shaft and rotates together with the auger. Once the auger reaches its final depth the shoe is knocked out and helps to provide better end bearing capacity of the pile.

After reaching the final depth a leakage test is carried out. If the plug was found to be water and soil tight, reinforcement is placed in the tube and concreting begins. Concrete mix is delivered to the top with a concrete pump. The concrete falls smoothly to the bottom of the pile. During extraction the auger is rotated in the same direction as whilst drilling in order to avoid mining soil and prevent spoil from getting into the pile.

It should also be noted that the rig is not only capable of installing vertical piles but also battered piles. The leader may tilt backwards up to 20% from the vertical and up to 10% in the opposite direction.