References
Grand Palais
FRANCE, 2001 - 2003
Underpinning the “Grand Palais”, built in 1900 and protected as a National Heritage monument, and creating a new retaining wall for a future underground structure in the main hall.
Completed in 1900, the “Grand Palais des Champs Elysées” was founded on alluvial soils of varying quality, deteriorating towards the south approaching the Seine river. The south part of the building was founded on wood driven piles supporting the foundation masonry. The recent lowering of the water led to rotting of the upper parts of the wood piles, and resulted in significant settlements. These reached up to 15cm, creating problems for the structure. In order to save this Historical Monument, the decision was taken to underpin the whole structure, whilst avoiding further distress. It was also decided to use this opportunity to install the required retaining wall for a proposed future underground structure to be constructed under the main hall.
Problem and his solution
Soletanche Bachy designed and installed a complex underpinning programme combining civil works, jet grouting and diaphragm walls whilst respecting two major constraints requested by the Owner:
- No additional settlement allowed.
- Keeping the adjacent Museum in operation during the works.
The structure was monitored with a Cyclops system operated by Soldata (an independently operated affiliate of Soletanche Bachy), which controlled the three dimensional position of 65 targets in real time.
Diaphragm wall
The diaphragm walls were installed hard up against the existing foundations, under 7 m headroom. The panels were keyed 1m into the limestone, without generating any vibration. This was made possible with a compact hydrofraise and a mud treatment plant located outside the building.
Jet grouting
The jet grouted columns were installed under the existing structures. The machines operated in very restricted areas, frequently with only 2.5m headroom.
Civil engineering
The civil works structurally linked the existing structure and the new foundations. Typically this involved reinforced concrete structures clamped to existing foundations by post-tensioning, allowing the transfer of load to the diaphragm walls or jet grouting. This method allowed the transfer of load without additional settlement.
Works continuation
After completion of the foundation programme, the rehabilitation of the metallic structure and the replacement of the glass roof were carried out safely.
Techniques
Regardless of site size, and providing it involves a significant proportion of works in the ground, Soletanche Bachy will handle the complete project, and all aspects of the works, including site supervision, excavations, foundations, civil engineering and all construction operations.
A diaphragm wall is a reinforced concrete wall that is made in situ. The trench is prevented from collapsing during excavation, reinforcing and casting by the use of supporting bentonite slurry. The slurry forms a thick deposit (the cake) on the walls of the trench which balances the inward hydraulic forces and prevents water flow into the trench. A slurry made of polymers can also be used.
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.
Ouvrages
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
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