Future-proof tunnel connects bike parking and subway distribution hall

Then the sheet pile walls were placed and the roof of this tunnel was already poured. At the time of this writing, this tunnel is already a real tunnel, only there is no passage to the metro hall yet. We speak with Celmis van Meerten, project manager for Metro Link Tunnel at Max Bögl & Partners.

"In the summer of 2020, at the time of TBGN 2 (streetcar decommissioning), all streetcar tracks were replaced on the west side of Station Square. At that time, sheet pile walls were placed at the spot where the tunnel was to be located and the concrete roof had already been laid on site. Then the excavation of the tunnel could begin," Celmis begins. He started in this project as the person responsible for cables and pipes and is now responsible for the breakthrough to the subway hall.

Almost light at the end of the tunnel

"We just poured the floor of the cuff. The cuff forms the physical connection to the subway station. So in the cuff, you're looking up against the wall that will eventually have to be removed to make the actual connection. The first breakthrough will be a modest hole, large enough for materials to go back and forth. This hole will be about 120 cm wide and 220 cm high. We may not make this working opening, however, until we have previously fitted the closed wall with a so-called toggle door. A fireproof and waterproof door, which provides a safe seal in case of emergencies such as fire and flooding. Only after we have mounted this toggle door on the wall can we create the required work opening. So there is almost light at the end of the tunnel, we may almost get to work with the box drill and wire saw."

Also thought of tomorrow's mobility

At the cuff, toward the bicycle parking lot, is the intermediate member. "That intermediate member can be removed in the future, so that in the future they can put a metro tube under the connecting tunnel, running from the east line to Isolatorweg. Now the ring line runs to Isolatorweg, but the last stretch between Isolatorweg and Amsterdam Centraal is not a subway. The subsurface space requirements therefore take into account the removal of the small tunnel so that the missing metro tube can possibly be laid." 

Current: the walls of the tunnel

At the time of the interview, work on the walls of the tunnel is in full swing. Celmis: "We are now working on the formwork and the reinforcement. Above the formwork are rows of pouring pipes; we will soon be able to pour self-compacting concrete into these pipes from ground level. Once that's done, then the next challenge comes into play. Then we will pour the transom beam and interior walls in the subway hall."

We ask when the time will come when the wall between the tunnel and the subway distribution hall will come out in its entirety. "That won't be possible until we have taken the same precautions that we have already made in miniature at the work passage. So an approved flood barrier must first be installed. This final flood barrier must be able to do its job in an emergency within 110 minutes. We make it from aluminum bulkhead beams, which have to be inserted manually. You might think it would be easier to apply a hydraulic valve, but that is not an option. The weight of valve and hydraulics would put too much strain on the metro hall. Before we get to the major breakthrough, the aluminum bulkhead damper must first be tested and approved. In the final situation, we will then have a water barrier on the tunnel side, and on the other side in the subway hall there will be a fire and operating closure."

Working in a complex environment

Celmis enjoys his work and still finds it special every day to be able to stand in places that will soon no longer be seen. "I also find it a powerful idea that thousands of people will soon be walking through 'our tunnel' and bicycle parking. It is working in a complex environment, with many challenges in terms of technology, stakeholders, permits and location, but that is exactly what we are going for. The big breakthrough is scheduled for the end of September, after which the finishing touches will take place and the installations will come in. By 2023 at the latest, it will be business as usual here again, and travelers will benefit daily from what we are building today. That's a nice thought, isn't it?"