a giant 17 meter nail drill

After years of comings and goings, on January 15, 2025, they began some works that are both expected and necessary in Madrid: the burial of the A5. It is one of the arteries of the city, an urban highway on which 80,000 vehicles circulate daily and which, after being completed in 1968, separated the residents of the neighborhoods of Aluche, Las Águilas and Lucero from those of Batán and Casa de Campo. The works will not be simple or quick, but there is a trick: the ‘cut and cover’ technique.

This technique is nothing revolutionary. It is one of the oldest and most used methods for tunnel construction superficial. When a tunnel has to be excavated to a certain depth or that passes through complex elements, the ‘boring machines’ or tunnel boring machinesbut when it is not necessary, this false tunnel is simply made.

In essence, the ‘cut and cover’ technique consists of excavating a trench from the surface, building the new road inside it and, later, covering it with fill material. And there are two variants:

• From bottom to top: The trench is excavated with the necessary support from the ground and the tunnel is built inside. Once the structure is completed, the trench is backfilled and the surface is restored.
• From top to bottom: First, the lateral retaining walls and the crowning beams are built at ground level. Subsequently, the roof is excavated and prefabricated beams are installed. Thus, the surface is reinstalled early to restore traffic as soon as possible while the excavation work and construction of the permanent roof are completed.

In the video above, a piloting machine in action. Basically, like a giant “drill”.

Each has its advantages and disadvantages, and are used depending on the terrain and conditions, but for tunnels at depths of about ten meters, these ‘cut and cover’ methods They are more economical and practical than tunnels drilled with deep tunneling methods.

The ‘cut and cover’ of the A5 and Castellana in Madrid

As we say, the technique was designed to hinder daily traffic as little as possible, and even more so on such essential and busy roads, but the reality is that on the A5, the works have converted one of the entrances to the capital into a ‘Mario Kart’. Through a series of detours, a succession of tight curves have been created at very slow speeds that have provoked that the Madrid City Council collects multiple complaints.

Such is the commotion that a guide to avoid getting lost with this burial of the A5but in any case, both the highway and part of Castellana have a few months of noise and excavators ahead of them. In the case of the A5, 3.2 kilometers of the highway are being buried using the construction technique of concrete containment screens to then install the covering slabs.

There are 600 people who work daily on the site along with a hundred machines such as the striking ‘pilots’. These machines are specialized in the construction of “piles”, which are nothing more than buried columns that can be built in the ground by injecting concrete into a metal reinforcement or that can be prefabricated.

On the route of the “new” A5, there will be more than 6,000 piles of reinforced concrete. But the highway is not the only area of ​​the city in which this technique is being implemented. In the Parque Castellana project, a tunnel of about 675 meters long is also being built that will have 2,041 piles.

In the end, and as we mentioned, it is not a new technique (in fact, it was used to build the Paris metro in 1900), but of the possible options for creating tunnels, it is one of the least disruptive to traffic in cities. Although those who are suffering from the works on Parque Castellana and the A5 will surely see it with different eyes.

Images | Xofc, Madrid Diary

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