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For the VDR project, Tjaden Adviesbureau voor Grondmechanica was able to maximize its expertise and came up with the necessary creative solutions aom to literally bring out the right information for client Heijmans.
For more than 50 years, Tjaden Adviesbureau voor Grondmechanica has specialized in geotechnical soil investigation, geotechnical engineering and geohydrology. “At Schiphol Airport we have been active for many years, both for the airport itself and for various (infra-)contractors performing work,” says Arjen Verhoeven, director of operations at Tjaden Adviesbureau voor Grondmechanica. “Our employees are aware of all protocols, safety requirements and are flexible in terms of deployment. Quick switching and thinking along in practical solutions are characteristic of our way of working. That was also a requirement on this project.”
At Schiphol, no spade goes into the ground until the work site has been scanned for the possible presence of unexploded ordnance. “In order to probe in suspected areas without problems, we use a cone with a so-called magnetometer,” explains Verhoeven. “This cone signals metals in the subsurface. This does not mean, that it is an explosive, but as soon as the meter gives a certain reading, the area is first investigated more closely. Incidentally, the measurement is monitored in real time by an expert on unexploded ordnance.”
Project VDR was a very varied job for Tjaden. “We carried out the necessary surveys both on landside and airside. Including soil borings and laboratory research to map any subsidence that would take place in the subsurface,” says Verhoeven. At the site of ProRail's two tunnel tubes, over which the new viaduct will be built, Tjaden made the most of his knowledge and experience. “There was no longer a view of the drawings of the tunnel tubes. Therefore, we used empty cone-less probing rods to probe how much space was present next to the tubes. This was to assess whether there was enough space to install the piles in a certain diameter. We also carried out probing in the middle verges of the A4 in connection with the piles of the new viaduct. This work was carried out mainly during the nights.”
So it was anything but a standard job for them as well, Verhoeven concludes. “It is a unique location with many ‘obstacles’ in the subsurface, and that makes it a great job for us and our employees. The cooperation with Heijmans and Schiphol is also very pleasant. We have built up a fine relationship with each other over all these years.”
