References
T 33 Tunnel
MONACO, 2005-2006
Road tunnel excavated through rock, 55 to 85 m² excavated section
The T33 tunnel in Monaco was excavated through rock with an excavated section of 55 to 85 m². The 140 m long tunnel links the place du Canton to the Monaco South exit towards Nice. As part of a larger joint venture, Solétanche SAM and Solétanche Bachy Tunnels, both subsidiaries of Solétanche Bachy, were awarded the contract for the specialist geotechnical works and for excavating and concreting the tunnel.
The immediate, highly sensitive environment required strict compliance with vibration restrictions and the development of innovative excavation techniques. An extensive ground monitoring system was put in place and used to monitor the reaction of adjacent structures during the different phases of the works.
The upstream drive heads
Once the retaining walls had been constructed for the two drive heads, excavation began with the upstream head which intersected the cliff obliquely, and immediately beneath the portal of the existing rising tunnel. in line with the rising tunnel head (T7). An innovative pre-cutting technique was deployed: preliminary cutting using secant boreholes designed to isolate the section of rock to be removed, followed by milling of the rock (highly abrasive dolomitic limestone) assisted by micro-mining splitting techniques.
The downstream head
The geological conditions required the installation of specific support structures in the form of pipe roofing and of heavy duty 220mm arched ribs.
Excavation works were carried out using a hybrid technique combining milling and drill and blast. Disturbance was reduced by forming a large decompression void by milling in the centre of the drive in advance of the drill and blast. The blasting pattern was governed by the requirement for a very low instantaneous charge. This required a very tight pattern with a large number of blast holes and the use of the entire range of micro delays on the 10 sequential lines of each blast. Sections of tunnel passing close to sensitive structures were bored by milling the upper half of the tunnel and removing the bottom half by drill and blast. This increased use of milling reduced the vibrations transmitted to the rock mass.
Concreting
Once the complex dewatering and sealing works had been completed, work was started on the permanent concrete lining. One of the specific features of the T33 tunnel is that it has 2 different cross-sections over a short linear length. A formwork tool that could be assembled and modified in the tunnel was designed to cover these 2 sections. Le tunnel T33 à Monaco est un tunnel au rocher de 55 à 85 m² de section excavée et de 140 m de long qui relie la place du Canton à la sortie Sud de Monaco en direction de Nice. Solétanche SAM et Solétanche Bachy Tunnels, filiales de Solétanche Bachy, se sont vu attribuer, au sein d’un groupement, les travaux spéciaux d’une part et le creusement et le bétonnage du tunnel d’autre part.
MAIN QUANTITIES:
• Excavation using explosives: 8,900m3
• Sprayed concrete: 6,322m²
• Waterproofing 3,500m2
• 280 type GEWI 25 to 32 rockbolts
• Reinforcement: 307 t
• 115 temporary ground anchors
• Tunnel concrete: 3,350m3
• 40 permanent ground anchors
• 300 micropiles
• Struts: 100 t
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 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.
A retaining shell is a slim shell structure used during vertical excavations. Unlike retaining walls, the weight of a retaining shell has little effect on its capacity to balance the pressures.
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
Soletanche Bachy has developed a number of techniques for use in road structures; cut and cover tunnels, viaduct etc.
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.
Voyage au coeur de l'ingénierie de pointe
Find out more about our expertise by:
