Toulon breakthrough

Miners in the Bouygues Construction-Colas-Screg-Soletance Bachy contracting joint venture equipped with a long-armed hydraulic breaker broke through in the second Toulon Tunnel in France this month, completing a total length of 1818m. Permanent lining work then began, together with work on retaining walls and tunnel partition structure.

The tunnel was designed to relieve congestion on the busy east-west coastal highway, which was already served by one tunnel bore constructed in 2002 under the city. The road links Marseille with Nice. The project owner was the regional highways authority (Provence Alpes Cote d’Azur - PACA) with project management by Setec TPI and Terrasol, and technical consultancy from the Centre d’Etudes des Tunnels CETE Mediterranee.

Tunnelling began on 10 September 2007 and was due to complete at the end of last year, but ground conditions requiring stabilisation made progress difficult. The tunnelling benefitted from intermediate ‘attack’ points from shafts. Work continued on a 24-hour basis for six days a week, with most surface activities under an acoustic canopy to minimise disturbance to residents. The construction cost was recently reported as EUR 292M (USD 411M).

In addition to the mined tunnel there were cut-and-cover stretches of 210m length at the west end and 200m to the east. The whole tunnel, including other drives, measured 2.9km.

Excavation featured an unusual gantry rig known as the GTA. One was used at each of the two main faces. Designed in Germany, and first used in France, it has been in use since April 2008. It was equipped with two access baskets and two drills on articulated arms. The weight of the whole unit is 70 tons. It was fully automated under remote control by surveyors to ensure the accuracy of movement and to adapt to the geology encountered. The machine was suspended from two guide rails in the tunnel crown and was used for all face work except the excavation itself. The exact excavation and primary support procedures will be described in a later article in T&TI.

After the completion of concreting the various equipment and systems will be installed including ventilation, signals, lighting, barriers, security and CCTV, and monitoring. The traffic management and information centre is also due for renovation, and finally the surface amenities will be restored. Commissioning was scheduled for mid-2013.