It is approximately 100 meters long, weighs 1,500 tons, takes an approximate construction of three months and has a strength to excavate 15 meters per day; Which will facilitate underground progress of 500 meters per month. This is Merritt, the tunnel boring machine responsible for this … Making the expansion of Line 11 of the Madrid Metro a reality, which will build tunnels for the Comillas and Madrid Rio stations and which will connect Palos de la Frontera, Atocha and Conde de Casal. ABC was able to access the assembly work of this huge machine, about 10 meters high, which arrived in the capital from Germany with the aim of accelerating the construction of the large cross-line of the Madrid network.
The packages, approaching a hundred, will continue to arrive at Comillas Park – where cranes and building materials are installed today, but in a few years will include several thousand square meters of green space – until December 19. These pieces have made a 2,000-kilometre journey by sea and land, which began at the German factory Herrenknecht AG, in the town of Schwanau, and where Dulcinea and Tizona also left more than twenty years ago, the engineering work that allowed the construction. From the M-30 tunnels.
From Santander, the Spanish port where the parcels containing the total puzzle being assembled today arrived, they were transported in trailers to the capital. Naturally, all these movements are carried out taking into account that the material will touch the capital’s land at night so that it does not affect traffic in the area as little as possible.
Beneath the surface of this park in the Carabanchel region, planning has already begun for what will become Comillas Station. From here, one can only imagine by looking at the skeleton of the different levels, which can be seen through the open hatch to transport the different pieces of Merit to their assembly point, where the lobby, turnstiles and escalators will be; And at a depth of 25 meters, the paths on which the suburbs will spread.
This is where the heart of the machine – the multiple motors that will power the machine – and the brain of the machine – where the engineers will work – are reassembled piece by piece. Tunnel boring machine. This process will continue, according to what José Pablo Castro, director of the tunnel, confirms to this newspaper, between 5 and 8 weeks. In the remaining time, technicians will be responsible for assembling the rest of the cabins and systems that make up this approximately 100-metre-long machine.
A sample of one of the sections that will be installed inside the tunnel
Once the tunnel boring machine – named after the name given to the city of Madrid by Muslims – operates its engines, it will go from digging 10 meters per month using traditional technology to progressing 15 meters per day. In addition to excavating the ground, loops of tendons that will form the tunnel will be installed at the same time. That is, the tunnel boring machine will dig and build, leaving the planning practically ready, so that the rest of the installations (platform, tracks, catenary, etc.) can be carried out later. 3,500 of these rings, whose height exceeds 8 meters, have arrived in the capital.
In the construction of the suburban section that will connect the Comillas and Conde de Casal stations, more than 210,000 cubic meters of concrete will be used – equivalent to 84 Olympic swimming pools – and 32,000 tons of steel – four times the weight of the Eiffel Tower.
Technicians will work to assemble the Merritt until February 2025, when tests that will allow the tunnel boring machine to start its engines will begin in March.
The heart of the machine
However, the main piece of this massive machine is the cutting wheel, a toothed structure that will head the tunnel boring machine, type EPB (‘Earth Presure Balance’), which has been specially designed to suit the characteristics of Madrid’s terrain. The reason why there are no two identical wheels in the whole world.
The geology of Madrid, specifically the area through which the tunnel boring machine will be operated, consists of piñuela, coarse and black clay. Thus, the piece was designed using 54 cutting discs or “crushers”, which are the main cutting elements; 196 supports are responsible for the holes and beams, and they are elements that have the function of pulling the material out of the room. They are all distributed on the surface of this wheel, at the front of which appears the flag of the Community of Madrid.
During tunnel formation, technicians must check the wear of these elements – although each has different functions, they complement each other in the final work – and replace them when the wear standard is reached. In theory, the “crusher” should be changed with every kilometer traveled, as planned by the technicians responsible for this work. But “sufficient leniency to intervene sooner if necessary” was also taken into account. Moreover, this structure is covered Protectors that will prevent increased wear.
The collection times they are running extend until March next year. “In November and December, all the parts will be received, in January the assembly will be completed and in February the tests will be carried out to start at the beginning of March,” Miguel Nunez, General Director of Mass Transport Infrastructure for the Community of Madrid, told ABC.
Once in operation, Mairit will work seven days a week, 24 hours a day, to advance the excavation work, but as work resumes at a faster pace, technical stops will have to be made to check not only the wear of the main part, but also carry out maintenance tasks or change the oil.
Merritt’s excavation work to create the suburban tunnel will generate tons and tons of soil, which will be deposited, and transported by chain, into an 8,000-cubic-meter pit. “It was built specifically to house this while the trucks took it out. Thus, it will allow the storage of what is generated for three consecutive days and prevent it from stopping at any time,” says Núñez. The groundworks that will be carried out during this performance amount to one million cubic metres, which could fill two stadiums the size of the Santiago Bernabéu.
Assemble the tunnel boring machine in the place where the drilling will begin
Once Mayrit does its part and shuts down its engines – which according to community calculations will be in 2027 – the first section of the extension of Line 11 of the Madrid Metro will be practically completed, with a total of 6.6 kilometers of tracks. However, this is just the beginning of the major regional project, with an investment of 518 million euros, which seeks to create a line that will cross Madrid from south to north and connect Cuatro Vientos and Valdebebas via 20 stations. This would allow a connection to the Atocha station or Terminal 4 in Barajas.
Through this project from the government of Isabel Díaz Ayuso, communications will be facilitated for thousands of citizens, in addition to reducing emissions by 90% before 2050.