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Vibro replacement underpins Dusseldorf monorail

GERMAN FOUNDATION contractor Bauer Spezialtiefbau has completed extensive vibro replacement work for the new suspended monorail link between Dusseldorf International Airport and the nearby ICE railway station.

The link, which will ferry passengers from the high speed rail terminal to the airport, crosses over worked gravel pits that were backfilled with demolition and building rubble. The guideway support columns are founded on 40,000m of stone columns installed by vibro replacement using the company's TR17 deep hydraulic vibrators.

During vibro replacement, the vibrator is lowered to the design depth both by vibratory impact and under its own weight. This laterally displaces the surrounding soil and densifies it. Jets of compressed air assist penetration and maintain an open annulus around the vibrator. This allows granular backfill, tipped into the borehole at ground level, to flow freely around the vibrator to the tip. Repeated lifting and lowering of the vibrator then compacts the granular material and displaces it laterally into the surrounding soil. It is claimed that soil stiffness can be increased by two or threefold by the process.

Quality control for the Dusseldorf job was provided by a monitoring system specially designed by instrument manufacturer Jean-Lutz. A number of sensors installed on the machine recorded data which was processed to produce pressure-depth diagrams.

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