Because the tunnel is bored, hardly any digging is needed in the Green Heart Area, which minimises environmental damage and disruption due to the construction.

The bored tunnel starts at Leiderdorp, close to the Does canal. Just south of  Westeinde, a long streched street in Hazerswoude-Dorp, the tunnel surfaces again. The high-speed train will speed through the tunnel in approx 90 seconds with a speed varying between 250 and 300 kilometres an hour. The tunnel consists of a single tube with a length of over 7 kilometres. Including access ramps, the tunnel length comes to 8.5 kilometres. The outside diameter of the tunnel tube is almost 15 metres. This size makes the tunnel unique in the world. A concrete wall divides the tunnel in half, creating two separate ducts for the double track. The tunnel was constructed with a purpose-built boring machine.

The boring machine, named 'Aurora', started its work from a construction shaft that was 25 metres deep, the so-called start shaft. In view of the boring machine's size, the start shaft measured 30 metres in width and over 80 metres in length. From this shaft, the tunnel boring machine commenced its journey at a depth of 30 metres to the end shaft, 7,160 metres further south. Boring at a depth of 30 metres meant that the boring machine and the hollow tube that was left in its trail had enough earth and weight above them to prevent the whole structure from being pushed upward by the groundwater.

The construction process hardly disturbed the groundwater streams, because the 15-20 metres of soil above the tunnel always allows enough space for the groundwater to pass above and under the tunnel. 

The start and end of the tunnel, the so-called access ramps, where the tunnel descends or rises 30 metres, could not be bored. Accordingly, both the closed and open parts of the access ramps were dug. The access ramps are basically huge concrete tanks – partly with an open roof, partly closed.

To affect the groundwater level in the vicinity of the access ramps as little as possible, these concrete tanks were built in sealed-off construction pits, lined with so-called deep walls. The deep wall panels reach 25 metres into the ground and anchor the concrete floors of the two construction pits. Only those parts of the access ramp construction floors that were less deep had to be pile supported. 

For those parts that were situated at less depth, steel pipes with a diameter of 1 to 1.5 metres were used as piles. This meant heavy-duty piling. When the construction pits allowed for less deep piling, the steel pipes could be replaced by lighter, steel sheet piling, making the piling work also lighter.

After driving the sheetpile walls and installing the deep walls, the soil was removed down to a few metres below the bottom of the projected tunnel. When the digging was finished, the excavation had groundwater in it, as was expected. At that point, a watertight floor of underwater concrete was poured on the bottom of the construction pit. To prevent this concrete floor from being pushed up by the groundwater after draining, the floor is held by so-called tension piles.

When the construction pits were finished, the tunnel access ramps were built of reinforced concrete. In the meantime, these access ramps and the deep shaft have been covered with earth from the same area. For this reason, this building method is also called cut & cover. The roof and the areas around the access ramps are brought back to the original state as much as possible. The open part of the access ramps remains open and visible.

The work on each access ramp took around twelve months.

The excess dug-out earth is stored in temporary depots. The final use of this earth was the subject of negotiations with various parties. After removal of the boring fluid and any salt from the partly brackish groundwater, the sand that is released from the bored tunnel may be used for raising terrain or road construction.

The total construction of the bored tunnel takes more than five years. Construction started in the autumn of 2000 and will continue to mid 2006. In the last phase, the finishing work on the tunnel is carried out, meaning: laying out rails, and installing overhead wires and safety systems. Most of these activities are done underground and cause relatively little inconvenience. In addition, the surface is restored to its old state as much as possible.

• Length of bored tunnel: 7160 metres; or 8670 metres including access ramps.
• Length of access ramp at Leiderdorp: 713 metres; 
• Length of access ramp at Hazerswoude: 768 metres;
• Diameter drill chuck: 14.87 metres.
• Depth of tunnel: approximately 30 metres under Normal Amsterdam Water Level.
• Concrete partition wall: 10 metres high and 0.45 metres thick.