A stable foundation thanks to 3,130 grout (injection) anchor piles

The foundation of the ramp on the north side was laid by Jetmix with its specific, self-drilling grout (injection) anchor piles, which can absorb higher forces than the GEWI anchors on the south side.

Over a stretch of 500 meters, Jetmix installed as many as 3,130 anchor piles, equivalent to 159 kilometers of drilling length. "The ramp is constructed as an embankment with a gradient of 4%," explains Edwin Giljam, Jetmix's operations manager. "We deepened the anchor piles from ground level, creating a free space for the purpose of excavating the construction pit. In the most extreme case, we were at a depth of minus 63 meters NAP (!) with a disconnection level of the drill rod at minus 28 meters NAP, the depth at which the pit is excavated."

Jetmix anchor post system

The self-drilling grout (injection) anchor pile system is an in-house development of Jetmix. The anchor pile system is produced by Geotech Metals. "At the Blankenburg connection, we applied a number of variants of the grout (injection) anchor pile system in diameters of 82.5, 101.6 and 114.3 and in varying wall thicknesses ranging from 12.5 to 28 millimeters. The pile system basically consists of sections of 6 meters of hollow tube that are threaded on the outside with a drill head at the end. Through a rod in the hollow tube, we bring the grout mixture up to the drilling tip. The mixture provides lubrication for the drill head, on the one hand, and on the other hand, to convey the material upward through the tube. Because of ammonium acid contamination in the subsurface, once at depth the borehole is filled with a mixture in a different mixing ratio that is more resistant to penetration. Then the extension rods are disconnected from the anchor pile system via a bayonet coupling and we bring these rods back up."

When the cofferdam is excavated, the Jetmix pile system is fitted with a saucer construction to create a connection with the underwater concrete to be applied later. Giljam: "So in the final situation, our pile system can take both tension and pressure. We spent approximately one year full time installing the 3,130 anchor piles. In the process, we used five of our own KLEMM 807 drilling machines. Just before the 2020 construction vacations, the last pile was installed. We look back on an intensive but highly efficient project. Not least thanks to an in-house logistics center that we had set up on site."