Driving two-metre piles to a depth of sixty metres? The impossible has been made possible. Strukton Infratechnieken has developed an entirely new piledriving technique for the North/South Line in Amsterdam: vertical microtunnelling. This new tunnelling method can be used to drive piles with a wide diameter down to great depths in places where the working height is extremely limited. A relevant example is the replacement of the old foundations under the platforms of Amsterdam’s Central Station. The extensive inconvenience and costly collateral damage caused by conventional piledriving and vibration techniques are avoided.
Microtunneling (CMM) piles create a tubular pile wall under the yard of Amsterdam’s Central Station. This earth and water-retaining wall provides a solid circular cofferdam into which tunnel units can be sunk at a later stage in the construction process. But the circular cofferdam and the new floor will also provide the new foundation for the yard.
This works as follows: the CMM equipment consists of two machines: a driving frame and a portal crane. The portal crane lifts tube sections up to two metres in length from a wagon and places them in the driving frame. The wheels on the driving frame can be retracted to allow the portal crane to pass. During drilling, the driving frame is positioned just above the existing concrete floor. The driving frame stands on lion anchor piles that give it its driving power.
The driving frame consists of large clamps: a fixed clamp under the frame and a vertically mobile upper clamp. By holding the tube sections in its clamps and making vertical movements, the frame guides the tube section into the ground. The first section has a hydraulic drill bit. Once the pile is driven, the drill bit collapses and is pulled up to be used for the next pile.
The microtunnelling machine starts driving three non-adjacent tubular piles measuring sixty metres in length. The tubular piles are filled alternately with concrete and sand and all driven into the ground in the same manner. The piles have alternating lengths of thirty and sixty metres. This technique has also been successfully used to build the foundations for the new IBIS Hotel near Amsterdam’s Central Station.
Please visit the Strukton Infratechnieken website.