Rod anchors aligned with geotechnical engineering

Groundwater pressure under the tunnel floor caused one of the tunnel segments of the Princess Margriet Tunnel in the A7 to rise in December 2022. Further investigation revealed that a number of tension piles had failed. Reason for Rijkswaterstaat to renew the entire foundation with over 1,050 new tension piles from ANP-Systems. The SAS rod anchor system used here is ideally suited for this type of project. An interview with Remco van der Voorden and Henry Verdaasdonk of ANP-Systems. 

In late January 2023, ANP-Systems was contacted by the company Volker Staal en Funderingen asking whether the SAS tie rod anchor system was suitable as a tie rod for the foundation repair of the Princess Margriet Tunnel. "That was in fact the starting shot of an intensive period of several months to jointly arrive at the right solution and detail tuning for the new tension piles," says Henry. "Subjects such as service life considerations, the method of corrosion protection, the resistance to dynamic loads and detailed solutions regarding the connections between the rod and the floor passed in review. In between, we were also able to supply a number of test piles with which the soil-mechanical bearing capacity was tested locally."

Screwable bar anchor

The SAS bar anchor system is a well-known product in geotechnical engineering and is widely used in the form of anchor piles, wall anchors and laying anchors, among others. "The bar anchor features a coarse rib structure, which at first glance resembles a rebar. The major difference, however, is that the rib structure is oriented such that the SAS bar anchor is screwable along its entire length. For geotechnical applications, we have several steel grades available and all are deliberately mechanically matched to a geotechnical application. A tremendously wide range of sizes is available including all kinds of matching fittings. The rods can be provided with double corrosion protection or also electrically insulated if required," Remco explains. 

Project-specific solutions

ANP-Systems is also able to provide project-specific additional solutions. "In this project, the rods over the upper 4 meters are provided with a plastic sheathing that is necessary to achieve detachment from the substrate and also provides capacity against lateral movement of the pile." 

Because of the continuous pressure of the groundwater, the contractor uses a specific drilling technique. Henry: "The borehole is sealed with a valve each time. Within that system there is only limited space to fit the SAS rod anchor of Ø63.5 mm. In cooperation with the factory in Germany, we modified some parts to fit the intended drilling technique. And so, in a joint process, we arrived at the most optimal design." 

Reliable availability

The SAS rod anchor system will be delivered here by ANP-Systems in phases. After all, the foundation repair is also being carried out in phases since part of the Princess Margriet Tunnel is still in use. "Because in the first phase the design was not yet final, we also delivered a series of bar anchors in large lengths. Transporting rods 30 meters long by road is quite an undertaking," assures Henry. 

In addition, quantities in production rolls were reserved in advance in consultation with the project team to ensure reliable availability. 

Meanwhile, ANP-Systems has already delivered some 680 units of SAS bar anchors and deliveries will continue until the third quarter of 2024. "ANP-Systems' representation in Benelux can switch directly from stock positions in Austria and Germany or, as in this case, directly with the factory from rolling."