Concerning the four stations and two special structures
These six elements have kept the special works teams busy for the past two years. This has involved some 130,000m3 of diaphragm wall, excavated using a hydraulic grab and a Hydrofraise®, almost 70km of drilling.
These structures have now been backfilled, or else this is underway, and the internal structures are under construction.
The Friche Arrighi site is largely taken up by surface installations to facilitate operation of the TBMs.
One might have thought the special works teams were practically finished, and yet there is much left to do.
The auxiliary structures – The best till last
The main line is punctuated by the presence of four circular shafts located between the stations.
They will ensure access for the emergency services once the line is in use, along with ventilation and smoke extraction from the tunnel. These “smaller” works have an internal diameter of around 19 meters. They are made of a diaphragm wall with a thickness of 1.2m, with depths of between 50 and 68m. A fifth additional structure, the 1404P, located on the SMI loop, will allow emergency access to the service tunnel. This rectangular structure is made up of eight 1-meter-thick panels to a depth of 49m. The particularity of work on these elements was the extremely tight working space in a dense urban environment. In some cases, the slurry treatment plants were displaced to adjacent sites.
Each of the auxiliary structures is joined to the tunnel by branches dug using the traditional method. To ensure safety during this phase, waterproofing by injection of bentonite slurry was first carried out.
The first of these structures to be finished for special works was 1402P, which was completed at the end of March.
The second on the list was the 1404P, whose walls were completed by the end of May. The site will continue this year with micro-Berlin type walls and an injected bottom, before handing over to the civil engineering and backfill teams. Special works will return for the freezing phase of Sables de Beauchamp, necessary for the excavation of the connecting tunnels in 2021 once the TBM5 has been through.
As for structures 1301 and 1501, they are at the injection phase of the connecting tunnels, prior to installation of the diaphragm walls. This will continue into autumn, when work will start simultaneously on their respective diaphragm walls.
The VDM station is currently being backfilled. The teams from civil engineering and earthmoving are taking turns on site to dig down to a depth of 52 meters. They will soon be joined by special works teams, who will carry out compensation drilling and freezing to make digging the cavern safe. To do this, a bespoke machine called the “Butterfly Drill” has been specially designed for this site in conjunction with the technical equipment centre at Montereau. This allows sub-horizontal drilling over a distance of some 70m, using a Hi’Drill® head, under pressure, with a deviation of less than 1%.