RER C - castor
RER C tunnel renovation using jet grouting restrictive urban site.
Every year, during the summer months, the Réseau Ferré de France undertakes renovation work on the RER line C on behalf of the SNCF. The method adopted for foundation reinforcement consists of installing jet grouted columns below the tunnel invert and along the side walls. This programme of maintenance works has been given the name “Castor”. Solétanche Bachy has been working on the project since 1997.
A jet grouting solution
The jet grouting process consists of breaking down soil structure at x m depth, from a small diameter (100mm) borehole) using a high pressure jet of cement grout in order to create a 1.50m diameter soil-cement column. The columns are constructed in split spacing sequence: primary, secondary and tertiary. The process is constantly monitoreded by recording drilling and jet pressure settings, followed by specific checks on column diameter either by means of core drilling or by electric cylinder survey, a method developed by EDG, a Solétanche Bachy subsidiary.
The importance of organisation
A 4 to 5 week period is allocated during which rail traffic is completely suspended. These works require the deployment of a faultless organization including teams that will work 24 hours a day, 7 days a week without inconveniencing the neighbourhood. The fixed site installations cannot be accommodated in the tunneland are hence located on the embankment of the river Seine. Equipment set up in the openair, such as pumps or compressors, are soundproofed. River barges are used to supply and remove materials. Solid waste is stored on big-bags inside the tunnel and then removed during the night to skips outside the tunnel or by work trains.
The tunnel sections for renovation were located between the Saint-Michel Notre Dame and Paris Austerlitz stations. These sections required 950 jet grouted columns including 284 along the side walls. Approximately 300 personnel were mobilised for the successful completion of these works.
The tunnel section for renovation stretched between the Ecole des Beaux-Arts to the Musée d’Orsay. 390 jet grouted columns were produced over a 4-week period, including 190 along the side walls. 120 personnel were present on site during this period.
Jet grouting is a construction process that uses a high-pressure jet of fluid (generally 20 – 40 MPa) to break up and loosen the soil at depth in a borehole and to mix it with a self-hardening grout to form columns, panels and other structures in the ground. The parameters for the jet-grouting process and the desired final strength of the treated soil depend on a number of characteristics, such as the soil type, the technique used and the objective to be reached. In granular soils, the high-pressure jet breaks up the grains through erosion, while in a cohesive soil, such as clay, the jet breaks the mass up into small particles. High pressure is needed to produce the kinetic energy required for the jet through a small-diameter nozzle. Waste material from the process (a mix of soil, water and binder) is recovered at the surface before being taken away for disposal.
Soletanche Bachy has helped build most of the world's major metro systems, performing soil consolidation grouting and constructing cut-and-cover tunnels with cast-in-situ diaphragm sidewalls, bored tunnels and major underground openings.
Soletanche Bachy has developed a number of techniques for use in railway works; cut and cover tunnels, highways, underground stations, viaduct etc.
These works are carried out to reinforce foundations that have degraded with time or have been damaged by events. Where a structure is to be subjected to higher loads or forces than it was originally designed for, underpinning of the foundations is often required as part of its upgrade.
Voyage au coeur de l'ingénierie de pointe
Find out more about our expertise by: