Following the collapse of a section of the pavement on the path of the tunnel of the 2nd tramway line of Nice, work longer than originally planned were needed. Laurent Carrere, the director of the project on the Metropolis Nice-Côte d’azur, made the point on this site.
The incident should be solved in a few days. But the formation of a hole capable of swallowing a pickup truck in the middle of a busy street of Nice finally need more than a month of work. The collapse, which occurred at the beginning of the month of July at the passage of the tunnel boring machine tasked to break through the underground part of the 2nd line of the tramway, has therefore raised some technical concerns, as explained by Laurent Carrere, the director of the project at the Metropolis : “we thought We succeed to overcome it immediately, but the problem is not resolved“.
It reveals the extent of the disorder : “We are in the presence of the excavation, can be carried out during the construction of the building on the side in the 1960s, which have been filled with anything : stones, tiles, scrap metal…”. Materials that are caught in the cutting wheel of the machine located a few meters below, forcing them to stop to empty it. The affected area does not measure more than 3 meters wide and 5 to 6 metres long but its nature, unstable and heterogeneous, has imposed to stabilize the edge before resuming work. Laurent Carrere continues : “We have launched operations of treatment of the field, with a series of injections of concrete around the tunnel in order to block the ground about fifteen metres“.
A small area treated with the utmost celerity
Tram line 2 © Métropole Nice-Côte d’azur
The interventions that have been carried out drum beating, in order to limit the delay and to make the roadway to vehicular traffic at the time of reentry. “At the request of the mayor of Nice, companies, are made 7 days on 7, 24 hours on 24, which has completed operations on August 15, and restart the machine the next day“, reveals the director of the project. For the anecdote, 45 residents bothered by noise from this project non-stop, even have been relocated to hotels for a few days. There remains, however, that the breakthrough took a month and a half late on his schedule.
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Laurent Carrère tells us : “It is infuriating, there were only 120 metres to go with the tbm, including 70 metres of slope to the surface, where the work of the soil had already been made. But we are now out of the area at risk and the machine should reach the output wells from 6 September. It was a hazard unpredictable“. It is still difficult to assess the impact of these setbacks on the overall schedule, but the commissioning of the whole line (including the section of the port) is still scheduled for September 2019. The director informs us, however, that shares of catch-up are in progress, in order to absorb a part of the delay. With regard to the traffic surface, it will be restored in the next few days, we he says.