At base level, the ground was raised slightly, to prevent groundwater overflowing while digging the deep wall trenches and to make sure that the trenches would remain stable.

At both tunnel walls, special concrete guiding beams were put in place. The trench digger's bucket is guided by these beams, of around one metre high, to make sure it digs in a straight line.

Special, low trench diggers excavated the ground for the deep walls. The excavation took place in stages (6 metres at a time, to a depth of around 30 metres) according to the size of the wall elements; the resulting trench was 0.8 to 1.2. metres wide and 6.5 metres long. During the excavation, the trenches were filled with a bentonite mixture. The bentonite supported the trench walls against collapsing.

To hoist the 30-metre high reinforcement nets into the trenches, there was no choice but to transgress into the obstacle-free zone. Therefore the high steel nets were hoisted into place at night. On the nights following a weekday, a crane was erected, the reinforcement net was hoisted into place, and the crane was disassembled again, all in 2.5 hours time.

The concrete was poured into the deep wall trenches through chutes. Because the concrete is heavier than the bentonite mixture, the latter was pushed upward. The bentonite was collected and then recycled. On average, it can be reused three times.

The deep walls had to harden for a few days, before the next element could be excavated. In this way, the entire, 125-metre construction pit was built, and in the end the top of the deep walls and the guiding beam were removed.

The earth between the deep walls was excavated little by little, to a depth of around 12 metres. After excavating a couple of metres, concrete props (transverse beams) were fitted that kept the deep walls in place. The groundwater level was reduced more and more through draining, which meant that the construction pit remained dry. As the deep walls were built into a deep layer of clay (35 metres below Normal Amsterdam Water Level), no water from the surroundings flowed into the construction pit. Additional, temporary props were fitted at the bottom of the construction.

When the construction pit was excavated to the proper depth, a construction floor was poured onto the bottom. The reinforcement for the tunnel floor has been anchored to the deep walls. Supported by formwork, the tunnel floor was then poured onto the construction floor. After several days hardening, the formwork could be removed. The result was an open tunnel, with the deep walls serving as definitive walls. At this location, the tunnel floor laid at a depth of 12 metres. The open tunnel trough and the deep walls together form an H.