References

Toulouse metro, B Line, Contract No 3

FRANCE, 2001 - 2005

Construction of 1.1 km of tunnel, an underground station and 2 shafts.

Under the framework of the Line B Underground project in Toulouse, Solétanche Bachy was awarded the works relating to Lot 3 as part of a Joint Venture. This involved carrying out works relating to the interconnection between Lines A and B (Jean Jaurès station), within a very dense urban area




Tunnels
Five sections of tunnel were excavated using a CSM Bessac compressed air tunnel boring machine (excavation diameter: 5.30m), comprising a total length of 1,068 m:
- 4 twin-tube tunnels for passing Line B through Jean Jaurès station,
- 1 tunnel for connecting Line B and Line A.

The path of the connection tunnel passed under various buildings and featured a curve with a radius of 95 m. The tunnel boring machine was specially designed to be disassembled and reassembled from the inside, thus removing the need to sink a shaft in a very dense area.
A 30m-long inlet gallery was also excavated, in divided sections, under the protection of pipe roofing. Temporary cladding consisting of metal arches and sprayed concrete was installed prior to application of the final cladding, which consisted of reinforced concrete placed using formwork.


Shafts
Two shafts were constructed using diaphragm walls and excavated beneath a slab (“top-down” method):
- the Victor Hugo shaft: 45 x 20m, depth: 23m,
- the Aubuisson shaft: 16.40 x 12.70m, depth: 28m.
The base of the Victor Hugo shaft was enlarged by an underpinning excavation operation (demolition of the diaphragm wall, excavation and underpinning after reinforcing by silicate grouting).


Station
Jean Jaurès station consists of two adjoining works constructed using diaphragm walls:
- the Line B station (an enclosed space that is 57m long, 24m wide and 17m deep),
- the Line A/Line B exchange area (an enclosed space that is 32m long, 37m wide and 17m deep).
The covering slab rests on a series of precast columns on barrettes which were then embedded in the final round columns supporting the station’s various floors. The works were excavated using a “top-down” method, with monitoring using real-time remote soundings. The civil engineering works were particularly complex because, as what was involved was an interconnection station, one of the lines remained in operation while the works were in progress.

Toulouse métro. B Line. Contract No 3

A528.pdf


Techniques

Civil engineering

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.

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).

Tunnel boring

In the tunnelling field, Soletanche Bachy’s subsidiaries Soletanche Bachy Tunnels and CSM Bessac specialise in management of tunnel sites and also, for the latter, the design and construction of tunnel boring machines.

Ouvrages

Metros

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.

Railway works

Soletanche Bachy has developed a number of techniques for use in railway works; cut and cover tunnels, highways, underground stations, viaduct etc.

Shafts

Circular shafts excavated inside a pre-formed cylindrical diaphragm wall only began to develop in a major way when modern plant became capable of digging almost perfectly vertical walls such that the cylinder can be considered self-stable without having to be tied back with ground anchors, or strengthened with struts or reinforced concrete rings.

Tunnels

In the tunnelling field, Soletanche Bachy’s subsidiaries Soletanche Bachy Tunnels and CSM Bessac specialise in management of tunnel sites and also, for the latter, the design and construction of tunnel boring machines.


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