References

Carré Royal - Reims

FRANCE, 2006

Facades underpinning and creating a new excavation within the perimeter of the former Galeries Rémoises.

Located in the historical centre of Rheims, the Carré Royal project involves the construction of a housing and office block comprising 5 floors including the ground floor on the site of a Galeries Rémoises building erected in 1923. The project retains the art-deco style façade and includes the construction of a deep basement car park. Solétanche Bachy has been awarded the contract for the facades underpinning the construction of the diaphragm walls and ground anchors and also for a temporary dewatering system.




Works were carried out over several phases:

Phase 1: micro piles
Prior to demolition works, Solétanche Bachy was responsible for installing the micro piled foundations used to support the façade and a shotcrete anchored wall, build against the wall of the existing 1st basement level. Active ground anchors have been installed through the backfilled cellar levels and anchored into the chalk. This sprayed concrete wall has been designed to take the thrust applied by the ground once the ground floor has been demolished.

Phase 2: diaphragm wall and grouted cut-off
The archaeological remains located in line with the wall were surveyed by archaeologists and then, once the internal structure had been demolished, these remains were removed and the cellars that had been undermining the basement were backfilled in order to render the excavation works safe. The diaphragm wall was then constructed within the preserved facades and from a working platform provided by the existing basement. This wall will enclose the underground car park and the foundations of the future building.
A dewatering system was then installed to lower the groundwater while the excavation works were carried out and the sealed floor cast. This system included a grouted cut-off under the foot of the diaphragm wall designed to increase the hydraulic cut-off, pumping wells and control piezometers.
The grouted cut-off was constructed in several stages: the wall bonded followed by primary and secondary grouting phases into the chalk, through open bore holes using that which had been previously installed and left ready for use.

Phase 3: ground anchors
The prestressed ground anchors and corner struts were installed as the earthworks progressed.

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Techniques

Diaphragm wall

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.

Ground anchors

A ground anchor is a load transfer system designed to transfer the forces applied to it to a competent stratum. An anchor is said to be temporary if it has a lifespan of under two years and permanent if the lifespan is over two years.

Grouting

Grouting involves the injection of a pumpable product (slurry), which will subsequently stiffen, into the soil or into man-made material (masonry), in order to consolidate the soil or structure or make it impermeable, through filling all the voids it contains. The slurry can fill the voids in the ground, the cracks within rock, solution cavities (it is then referred to as fissure and permeation grouting) and/or displace the surrounding soils through a bottom-up process or by fracturing (compaction grouting or solid injection - see the section on the subject - and strain injection). Grouting with soil displacement may be used to prevent potential damage to the structure brought about by excavations (galleries and tunnels, major urban excavations, etc.) and this is called compensation grouting (see the relevant section).

Piles and micropiles

A pile is a structural element driven into the soil for transferring loads and prevent deformation. Its slenderness ratio is not limited.
Pile shafts can be uniform and rectilinear, telescopic and belled out.
Piles can be installed either separately or in groups. They can also form a retaining wall, a mixed curtain wall, contiguous piles, secant piles and composite curtain walls, such as Berlin walls and similar. Piles are also used as precast beams to be placed in the structure of the building they support.

Ouvrages

Rehabilitation of structures and underpinning works

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.

Urban excavations

Major urban excavations are one of the specialist activities of Soletanche Bachy. Such excavations are required for basements to buildings that are usually part of the foundations of the structure and also used for under-street car parks, cut and cover tunnels for roads, rail, metro and storm water tank...


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