Wall Formwork Land Tunnel Makes Optimum Use of Space PossibleFormwork in small space

Commissioned by Rijkswaterstaat (Department of Public Works), IXAS is working to extend the A9 highway between the intersections Holendrecht and Diemen: the Gaasperdammerweg. The work on the A9 is part of the road extension Schiphol-Amsterdam-Almere (SAA). Until 2020 the A9 Gaasperdammerweg between the intersections Holendrecht and Diemen will be widened to five lanes in both directions including a reversible lane. About 3 kilometers of A9 Gaasperdammerweg will come under a tunnel. As a result, the air in the residential areas along the tunnel will be cleaner and quieter. A big park will be created above the tunnel that connects the neighborhoods in Amsterdam South-East with each other, which eliminates the current physical barrier between the districts of the Bijlmeer (north of A9) and Gaasperdam (south of the A9).

Particular architectural and infrastructural feats are required for the construction of the tunnel. Hendriks Precon delivers its contribution with a steel formwork that allows the contractor to maximize the use of the available space.

Land Tunnel Gaasperdammerweg
Since part of the project is to improve living quality, a – partly deep – tunnel will be built between railway Amsterdam-Utrecht and the Gaasp River. The tunnel itself is composed of five tubes: two for leading the traffic on the A9, one for a reversible lane and two outer tunnel tubes for the entering-exiting traffic. Each tunnel tubes will be three kilometers long, which makes the tunnel the longest in the Netherlands.

Tight Space
Widening the highway and construction of the tunnel will bring their own particular structural challenges. A9 remains open during the construction. Initially, the lanes will be slightly shifted. Then a reversible lane will be constructed, which comes to lie in the final phase between the 2 x 5 lanes. Because the water retaining function of the A9 should remain intact during and up to the final stage of the construction, dam walls will be placed. Then a piece of the A9 will be removed and the tunnel will be laid.

In order to maximize the available space for the land tunnel, the walls of the tunnel will be built close to the dam wall. “In many points, there is no more than 15 cm space between the dam wall and the sides,” says Rob Vermeulen, planner of IXAS. “There is too little space for a conventional formwork. It’s also impossible to apply a single formwork with a range of 3 km. That’s why we were searching for a rewarding solution in the form of a reusable container, which Hendriks Precon appeared to be able to deliver in the form of a steel wall formwork.”

Modular Custom
Developing ingenious solutions, including sidewalls is one of the specialties of Hendriks Precon.
The molds possess a high compatible concrete pressure and the lengths can be tailored for each individual project. Rob Vermeulen: “The formwork of Hendriks Precon is only 10 cm thick and two middle rods per panel can be applied from one side. So actually from just one side you have full control over the formwork. Further, the formwork is fully made of steel, which makes applying the plate joints an old practice. The result will be a sleek concrete image.”
The applied formwork is based on standard modules of 2.5 meters. Rob Vermeulen: “These are assembled into sections of 12-13 meters. We use two complete sets of these for the tunnel.” The 12 and 13 meters long sections are not fixed to each other. “That’s why we work with overlapping pieces that ensure a clean finish and fast processing. We hardly suffer from leaking water because the central rods allow proper water release. After cleaning the formwork, it is moved by a crane. Everything goes exactly as we expect.”