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L9 tunnel-boring machine remains stopped eight weeks after the Sant Gervasi sinkhole
Eight weeks after the sinkhole that forced homes and businesses in Sant Gervasi to be evacuated, the L9 tunnel-boring machine remains completely stopped. The machine has remained around 40 metres underground since 7 July, and the Generalitat has still not set a date for resuming excavation towards Lesseps.
The incident initially affected eight buildings, with 93 homes, as well as a dozen businesses. Residents of four properties have already been able to return, but the rest remain housed in hotels or relatives' homes while consolidation work and inspections of the buildings progress.
The wait is dragging on particularly in the buildings closest to the sinkhole. Further cracks and a small underground cavity appeared during subsequent inspections, which made it necessary to reinforce the checks before allowing all residents to return.
Beneath their homes, the situation has not returned to normal either. The tunnel boring machine remains exactly where it stopped after the incident, and the priority now is to review drilling protocols before restarting a machine that still has around one kilometre to go before reaching Lesseps.
That final section is one of the most complex in the entire project. The subsoil is constantly changing in composition and combines granite, slate and less compact materials. This heterogeneity makes it necessary to continuously adjust the pressure at which the tunnel boring machine operates and to strengthen monitoring of the ground from the surface.
Technicians are investigating precisely whether an imbalance while passing through an area of slate may have contributed to the collapse. The Generalitat has not yet established a definitive cause and maintains that drilling will only continue once the new procedures have been reviewed and validated.
The stoppage has also coincided with maintenance work that had been planned just a few metres further on, but the construction schedule is once again subject to an unexpected problem. L9 has endured decades of construction, budget stoppages and technical difficulties before completing its central section.
For Sant Gervasi, the works have ceased to be something that happens only underground. Two months after the sinkhole, there are still closed doors, families living away from home and an immobile tunnel boring machine beneath the neighbourhood. Until it moves forward again towards Lesseps, every remaining metre will continue to have a technical dimension, but also a very everyday one.