The Directorate-General for Public Works and Water Management (Rijkswaterstaat) is working on a true mega-project: widening the Schiphol-Amsterdam-Almere road segment. The A9 Gaasperdammerweg project between the Diemen and Holendrecht junctions is part of this. This is where Sjaak Gerritsen, Tunnel Construction Coordinator, is working on the construction of a three-kilometre long land tunnel.
From the elevated personnel pedestrian bridge, the old A9 route at Bijlmermeer looks like a kilometre-long canyon in the flat Amsterdam South-east land. Wedged between steel sheet pile walls and blocks of earth wrapped in cloth, Rijkswaterstaat and IXAS are working on a three-kilometre long five-tube land tunnel that will be opened to traffic in 2020. At the bottom of the ‘canyon’ it is bristling with excavators, lifting cranes, leaders, reachers, dumper trucks and other equipment. Everywhere you look there are orange-coloured figures, seemingly walking around without any purpose. The layperson sees chaos, the expert sees a well-oiled machine.
Stick to the Plan
“This is a densely populated area,” says Sjaak. “The space available to us to do our work is limited. You could compare it to building on a stamp. This makes the logistics, such as the supply and removal of materials and the placement of lifting cranes, extremely important. During the preparatory work all this was given careful thought and solutions were developed. Through means of excellent planning and measuring, we are succeeding. 'Stick to the plan' is our motto here. Stick to the plans and agreements that have been made. In this ‘ant heap’ everyone knows exactly what they are doing, so that the work is carried out efficiently. We have achieved all of the specified milestones and are well on schedule.”
Temporary is Permanent
The last milestone dates back to 6 June 2016. This is the date on which we started working on the actual construction of the tunnel. Before this we completed numerous preparatory activities, including the completion of all permits, the rerouting of the A9 motorway, the construction and commissioning of the alternating lane, and the installation and anchoring of the sheet pile walls to ensure that the relocated A9 does not sink into the construction pit.
Sjaak: “Once the entire project is ready, the sheet pile walls will serve as a dam. This is necessary because today the A9 is located on top of a dike that will also be removed. A dike that plays an important role in keeping Amsterdam dry. It is a good example of another IXAS motto: temporary is permanent, which means that all ‘temporary solutions’ will as much as possible be given a permanent function in the overall project.
On 6 June, the nine pile-driving rigs went into operation. Sjaak points to a long hollow tube, over 20 metres in length. That is for the vibro-piles. The tube is driven into the ground and a steel reinforcement cage is suspended within the tube. Concrete is then poured into the tube, after which it is extracted with vibration, allowing the concrete to be properly compacted. “The pile-driving is very disruptive to nearby residents, which is why we are aiming to finish most of the pile-driving work this year. In total, some 10,000 piles will be vibrated into the ground. The tunnel will rest on these piles.”
Priority Tunnel Sections
The temporary access and exit ramps to the A9, halfway down the project, are resting on ‘reinforced soil’, firm blocks of earth packed in cloth. At these locations the first two priority tunnel sections will be constructed in the near future. The access and exit ramps will then be relocated to be on the top of the tunnel so that the reinforced soil can be removed. Three other sections, at the beginning, in the middle and at the end of the tunnel, also have priority. The service buildings will be constructed on top of these sections. These buildings will contain all of the technical tunnel systems for access (barriers), lighting, climate control and safety.
Sjaak: “We are constructing the rough structure, TTI is responsible for the Technical Tunnel Systems. The pile-driving for the priority tunnel sections is finished. We have since started work on the first wall reinforcements for the actual tunnel. These three sections are to be ready in October.”
Other milestones for the coming autumn are the completion of the alternating lane, the installation of a tunnel section below the railway crossing and the work remaining to dismantle the A9. The concrete work for the tunnel must be ready by the summer of 2017.
“There is still a tremendous amount of work to be done by everyone over the coming years,” says Sjaak. “But it will all come together. Cooperation within IXAS is running smoothly, like the most natural thing in the world. It is almost impossible to believe that in 2021 there will be a park at this location and that you will be able to walk from the Nelson Mandela Park to the Gaasperplas lake across the roof of the A9 motorway.”