The L9, the eternal work that already accumulates 6,000 million in cost overrun (and a sinkhole)

It is intended to be the metro work with the longest tunnel in Europe. But the L9 works have already earned the title of "historic" and "controversial" for years, both for the delays the project has accumulated since the first plans and for the 6,000 million euros of cost overrun, according to the Court of Auditors. And since this Tuesday also for the 8-meter sinkhole that has forced the evacuation of six buildings in the Putxet neighborhood of Barcelona. But, at what point is this work? Where is the tunnel boring machine going? How does this large machine work and how is the tunnel built? We explain it to you in six keys