Grands Goulets Tunnel Breaks Through in Gorges of VercorsThe breakthrough of the Grands Goulets tunnel on 27th April, 2007 is a historical milestone for the economic development and the tourist activity of Vercors in the Drome department, in southeastern France. This 1,710 m-long 7 m-wide tunnel, located at the heart of the regional natural reserve of Vercors, adds real value to this exceptional territory by making the existing road safer for all users.Tunnelling commenced in October 2005 at the uphill portal on a 150 m drive, and in February 2006 at the downhill portal, on a 1,550 m attack. The junction between the two faces is a major, highly symbolic date for the construction of the Grands Goulets tunnel. It represents for everybody a real relief in terms of safety and regional land planning of the Drome territory. Opening of the EUR50 million tunnel, partially financed by a EUR5.6 million European subsidy, is planned for the summer 2008. Project historyIn the past, the Goulets road was only a walkable road/path, carved out in the middle of the dangerous calcareous cliffs of Vercors. To develop commerce between the Drome valley and the Vercors high plateau, the general council of Drome decided in 1834 to construct the Goulets road. Work started in 1843 and the road was opened ten years later. That was an heroic construction feat. Unfortunately, many workers lost their lives during construction.The Goulets road RD 518 is carved out along the Vernaison river and connects Pont-en-Royans and Die through La Chapelle-en-Vercors. Goulets in French means bottleneck. It is an impressive road that winds its way up a valley above the narrow and deep gorges of Vercors. Carved out in friable rock, the road runs through a chain of short, unsafe tunnels. It is hardly wide enough at some spots for two cars to cross, the bends follow each other and traffic safety is a major issue. See a video of the road at http://videos.streetfire.net/recentvideos/13/fcb10c14-65c5-48e1-aba7-993101215782.htm In 2003 then in 2005, at the grandiose Grands Goulets where the road is caught between high rock walls, dangerous crumbling rock incidents convinced the department of Drome to launch urgently the improvement of the RD 518 by constructing a tunnel. The unanimous decision reflects the political will to face the worries expressed by a majority of residents about dangerous daily driving on this notorious mountain road.Further to an inspection audit carried out by SETE (Société d'Études Techniques et d'Environnement), the department of Drome made the decision not to reopen this passage to traffic due to the instability and dangerousness of the place. Indeed, the cliff overhanging the Grands Goulets worsens every day. The work undertaken on this section to consolidate the cliff did not help any better, until now, to prevent rock from collapsing. Only the rescue and maintenance crews will be allowed in the future to take this section.Construction of the Grands Goulets tunnel is needed to ease the burden of isolation on the Vercors communities. The objective of the tunnel is to allow a safe and fast access to the Vercors high plateau for the residents and numerous tourists. The project will boost tourism and ensure the future of the local economic activity.MORSE, an innovative, safe and cost-effective emulsion Out of the 1,710 metres, 1,680 metres were drilled and blasted. The tunnel is 4.30 high and its carriageway is seven metres wide, i.e. a cross-section of 64 square metres. The tunnel will be equipped with six 9 sq m escape galleries, for a total of 800 metres. Click fr/55 to read more.Bouygues TP was entrusted with civil engineering work while the lead engineering for design and construction supervision was commissioned to Scetauroute. The owner is the Drome department road directorate. Visit www.bouygues-construction.com and www.scetauroute.comExcavation of the tunnel from the downhill portal began first by using dynamite cartridges triggered by electric delay detonators. When the first 150 metres were blasted, the contractor introduced a new production and pumping process for explosive emulsions: the MORSE system of Nitro Bickford. MORSE stands for Module for Repumping and Sensitization of Emulsion. This explosive emulsion, the NITRAM TX1, contains ammonium nitrate, acetic acid and sodium nitrite. The mixture is prepared directly at the construction site, then pumped and injected into the blast holes previously drilled. Visit www.nitrobickford.fr or click on their logo. Firing is done by means of detonating fuses. This system is less dangerous and easier to handle than traditional explosive. It is also more accurate and offers a better output. The principal difference compared to cartridge solutions lies in the fact that the product inserted in the blast hole occupies 100% of the space and that there is no loss of energy due to the annular void that can be observed in traditional charging with cartridges.The MORSE technology is used at the Grands Goulets for the first time in metropolitan France, after successful achievements by Dragages Travaux Publics, a Bouygues subsidiary, at the Cheung Ching tunnel in Hong Kong in the early 1990s and the ongoing Salazie Amont water tunnel in La Reunion. The process is also used at the Modane and La Praz access adits to the future base tunnel of the Lyon-Turin high speed line and at other construction sites around the world. Click here.Rock supportTunnelling required the production of more than 10,000 cubic metres of shotcrete as the tunnel progressed. Shotcreting strengthens the ground awaiting the final pouring of concrete in formwork, thus allowing the personnel to work safely at the construction site.To reinforce the concrete rigidity, Dramix steel fibres of Bekaert were incorporated into the mix but then the contractor employed synthetic macro fibres of Chryso. This was an innovative premiere in France. These synthetic fibres ensure structural reinforcement, are manufactured from a mix of raw materials with high mechanical strengths and improve the concrete properties. Visit www.dramix.comAt the tunnel site, the use of these synthetic fibres made it possible to reduce by four the dosage initially envisaged with steel fibres and to increase the bending/punching performance. The shape and structure of this macro fibre, particularly flexible, reduced by more than 20% the rebound losses when shotcreting the walls, thus increasing safety for users. These synthetic macro fibres are incorporated into the concrete at a dosage of 1 to 8 kg/cu m according to needs. It reduces the placement time of the primary support and suppresses the second shotcrete layer to protect the waterproofing membrane. Visit www.chryso.comCladdingThe tunnel's structural concrete consists of unreinforced concrete dosed with 280 kg of cement per cubic metre. Its minimal thickness is 30 cm. Bouygues TP uses a formwork solution specially designed by Ducrocq Ingénierie Process (formerly Ducrocq Industries). It is a 12.50 m-long 160-tonne carriage. The tunnel form construction process follows the upward gradient. The steep tunnel gradient (4.71%) prompted Bouygues TP to opt for the so-called "pilgrim step" process, a special displacement technique of the formwork carriage. The machine advances like a working bridge pushed using supports, which avoids the use of rails and the risk of sliding. The remote-controlled machine covers 12.5 metres in 30 minutes, the time necessary to complete one concrete section. Approx. 20,000 cubic metres of concrete will be necessary for formworking in the Grands Goulets tunnel. Visit www.ducrocq-ingenierie-process.comMuck disposal and recyclingAbout 180,000 cubic metres of rock will be excavated from the tunnel and its associated structures. To safeguard the environment and because of the large volumes, it was decided to recycle the rock. This includes the loading and haulage of the rock from out of the place, its processing and sale. The rock will be crushed, recycled and stored in Saint-Laurent-en-Royans. The rock that cannot be re-used will be stored in a final dump site in Bourg de Péage.Concreting, waterproofing and drainage works are scheduled to be concluded in October 2007. A Delta®-MS tunnel liner supplied by Doerken is installed for waterproofing. The liner is installed with its dimples facing towards the shotcrete layer applied for stabilization and filtration purposes. The air gap between the dimples will form a continuous system of channels. This continuous drainage space will convey any water coming from the ground towards the drainage system without impeding its flow. Visit www.deltadry.com/bvf/ca-en/products/foundation_commercial/products/MS_Tunnel-Liner.php and www.doerken-holding.comAsphalting and painting is programmed in December 2007. Installation of the safety equipment will be completed in June 2008. The tunnel is slated to open in end summer 2008. 22/07.