Foundation combination is 'the invisible friend' of The Green Bow

"Without a foundation, nothing happens." A statement by Jan Leen van der Vlies, project director at Franki Grondtechnieken. Together with Voorbij Funderingstechniek, Franki Grondtechnieken forms the foundation consortium contracted by construction consortium De Groene Boog for the foundation work for project A16 Rotterdam. Jan Leen van der Vlies, Bart de Lange (project leader foundation combination Voorbij-Franki at De Groene Boog) and Erik Sandifort (project leader Voorbij Funderingstechniek) talk about a project of phenomenal size.

At the table early on

"We have been involved from the tender phase," says Van der Vlies. "For example, we had an engineer calculate pile, vibratory and pressure predictions, we conducted research into the accessibility of the site for the heavy foundation machines, and we participated in the final design (DO). In addition, we provided engineering capacity for De Groene Boog to make the execution design (UO) of 34 construction pits, namely access North, South and the closed section. Together with engineering firm M.U.C. and Hektec, the UO calculations were made for sheet pile walls, outrigger frames and anchors."

Various works

The foundation combination can proverbially be seen as "the invisible friend" of The Green Arch. As imposing as both companies are in view during the execution of the work, their operations are invisible when the project is completed. De Lange notes, "At peak times, as many as 33 foundation machines were working at the tunnel at the same time." Project A16 Rotterdam is divided into 3 sub-areas. Subarea 1 is located near the airport and includes the slip roads of the A13, subarea 2 includes the construction of the tunnel and subarea 3 involves making the fly-over, over the A20/Terbregseplein. "Throughout the project we encounter a mix of artworks, temporary and permanent," Sandifort outlines. "Our work is therefore very diverse: making earth retaining walls, pressing sheet pile walls, installing anchors, foundations with prefabricated piles (VSP), installing pile mattresses and making combi walls. All disciplines of our trade come by."

Rottemer Tunnel: piles placed with watchmaker's precision

"For the construction of the tunnel, we constructed a sheet pile pit with sheet piles covering a length of approximately 7 km. About 9,000 VSP combi piles were then installed in the 2.2 km long tunnel section," De Lange lists. "Looking at the tunnel, we started with the culvert under Bergweg, there the first sheet piles were pressed and vibrated in April 2020. About 7 km of sheet piling, two longitudinal screens and compartmentalization screens in between. In the construction pit of the tunnel, we used four types of VSP combi pile, namely core Octicon 480/tube 610, core Octicon 430/tube 560, core #350/tube 560 and a type with 320 square precast core in tube 508. The Octicon 480/tube 610 is new, there we made special molds for the cores and the drill tip." Van der Vlies says in conclusion, "The piles in the tunnel's construction pit were really installed with watchmaker precision." This extremely high dimensional tolerance is necessary because, in contrast to traditional working methods, the underwater concrete floor is directly implemented as a structural floor within this project. Thus, the piles must be within sharp tolerances in all directions so that the diving crews can install the underwater reinforcement baskets over the pile heads (with heavy GEWI rods embedded in them).     

Foundation work

Prior to the De Groene Boog project, the foundation combination carried out a major foundation work on the Thamesweg in Rotterdam in the two years before. Voorbij Funderingstechnieken and Franki Grondtechnieken are therefore well matched. Voorbij Funderingstechnieken is characterized by a very wide range of foundation engineering services, expanded with a strong position as a supplier of steel structures and precast concrete elements, including the associated engineering expertise. Franki Grondtechnieken has characterized itself as a specialist company in deep foundations in particular since the beginning of the last century with an extensive fleet of equipment in North-West Europe. Together they form a versatile, powerful combination.