Specialist drilling under very special conditions

At the end of 2022, the Prinses Margriettunnel in the A7 between Sneek and Joure was big in the news. Due to the failure of a number of tension piles combined with the pressure of groundwater, one of the tunnel segments had risen. "When we read the report in the media, we were already hoping we would get a call," says Adriaan van der Jagt, director of Van der Jagt Groep. And so it happened. "If it's big, complex or special, clients in the Netherlands and Belgium do know where to find us." 

Van der Jagt Groep has been a versatile specialist for 65 years and is called in by clients for the most challenging demolition and renovation projects. For example, Van der Jagt Groep made the difference in widening the A9 motorway between Badhoevedorp and Holendrecht, on the Oosterweel link around Antwerp, and now in restoring the Princess Margriet Tunnel. "We are restoring anchorage in a very special way on this challenging project," says Adriaan. "On these kinds of complex projects we feel like a fish out of water, because with our different entities we always come up with an appropriate and safe solution."

Cuff valve

After extensive investigation in the tunnel, it was found that the tunnel floor had come loose from the pile foundations. "To avoid similar problems in the future, it was decided to install new tension anchors under the entire tunnel floor except under the aqueduct," Adriaan explains. "After some tests and advisory conversations back and forth, we quickly took action." Van der Jagt Group first drills a hole of around 500 mm to 40 centimeters in the tunnel floor. "That hole is then cut out and fitted with a cuff valve by our client Volker Steel and Foundations. We then drill through the cuff a hole of around 200 mm another 2 meters deeper. With that we come out from under the tunnel floor. We then pull the drill up and close the cuff. This prevents groundwater from spewing up through the hole."

25,000 cuttings

Van der Jagt Group is drilling more than 1,050 holes through the tunnel floor in that way, into which Volker Steel and Foundations is installing the new tie anchors. "Before they drill the tie anchors, they spray dämmer through other holes, a liquid clay that stabilizes the soil under the tunnel floor to prevent washing away. These are also more than 1,000!   

For this we first drill a hole around 66 mm and then via a cuff valve a hole around 40 mm another 2 meters deeper. And so we have to make sure we stay ahead of the two anchor machines," says Adriaan. "In this, we follow the contractor's schedule, since the tunnel is also still in normal use for traffic. Once the anchors are in place, we drill another sixteen smaller holes of around 200 mm around the hole of around 16 mm in which cuttings are placed. These cuttings are used to "tie" the structure together, creating the link between the tunnel floor and the anchor head. In total, we are drilling over 25,000 of these cuttings."

Special corners

The family-owned company operates continuously with a club of 15 to 20 employees on the project. "In addition to drilling the holes and cuttings in the tunnel floor, we also drill tie anchors in the wing walls at very special angles and degrees from a work platform," Adriaan adds. "In addition, we are also doing demolition work in the median strip because the concrete quality no longer meets current standards. The viaduct was built just after World War II and Rijkswaterstaat is immediately taking the opportunity to perform life extension maintenance. So we will be scaling up in capacity even further on the project in the coming months."

65th anniversary

Van der Jagt Group celebrated its 65th anniversary in 2023. "That in itself is a milestone," Adriaan rightly states. "We are a close-knit family business with a motivated team of over eighty employees. Together we make the difference. We are strong in drilling, sawing, demolition and pile driving on large civil projects. When things get serious or complex, they ring our bell. The bigger or more complex a project, the more interesting we find it. Whereas we used to be known primarily as an "SOS service," nowadays we are involved as a full partner in a project at an early stage to make a difference here as well. The restoration of the Princess Margriet Tunnel is a striking example of this."