The burying of the A-5, the megaproject of the municipal government of José Luis Martínez-Almeida that will finally close a historic gap in the southwest of the city, will become evident this Wednesday to all Madrid residents with the inevitable traffic cuts on the Paseo of Extremadura, although it has been running since October.
These works, which will last two years, will limit by half the capacity of a radial road through which they circulate daily. 80,000 vehicles and more than twenty bus lines pass by. The result of this first phase of execution of what will be the future Southwestern Green Walk will cover 3.2 kilometers of the A-5, from Padre Piquer Avenue to Portugal Avenue, leaving one lane in each direction on the surface, which which will end 90% of the daily traffic in the area. Underground, the tunnel will have three entrance lanes and three exit lanes, the closest to the bus-HOV median.
However, for this pharaonic work, unlike what happens with Metro line 11, where Mayrit is opening the way or the southern bypass of the M-30, where Dulcinea and Tizona acted, for the burying of the A-5 TBMs are not being used, but rather a system called ‘cut and cover’. The tunnel boring machine, the civil engineers explain, is only used when you need to drill deeper, such as in the aforementioned southern bypass of the M-30, which runs 60 meters below the ground.
The system cut and cover‘ instead, it is used in more ‘superficial’ tunnels. According to this technique, the first thing to be built (and introduced underground) are the concrete walls of the future tunnel. These screens can be continuous or piled, with tangent or secant circular sections that form a type of wall. These will make up the sides of the future underground. Then, the experts add, so that there is no pressure from the ground, the cover, the roof, is added, hence the name ‘cut and cover’. Finally, the interior of the tunnel is excavated. Thus, a section is created that is not circular, like that of tunnel boring machines, but rectangular.
«The advantage of this simpler method is that it can be done in phases and avoids completely cutting the track. You can open areas on the surface once you have introduced the screens and the cover while you continue digging underground. Besides, generates less noise than others,” add the experts, who emphasize that this ‘cut and cover’ is a very common procedure in Madrid’s underpasses; It was even used for lines 1 and 3 of the Seville metro.
Less common is the installation inside these screen walls of geothermal probes, which will allow, upon completion of the work, awarded in two lots to civil engineering giants such as Acciona, Dragados, FCC and Ferrovial, to “take advantage of underground energy.” for public buildings close to the area,” explained the city council. The countdown for the new Southwest Green Walk to become a reality is underway.
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