County road RD 518 in the Drome department in southeast France was a sinuous road along the Vernaison river in the Vercors gorges, connecting Pont-en-Royans, Chapelle-en-Vercors and Die. The old road was hardly wide enough to enable two cars to cross, with numerous short unsecured tunnels. Drivers who preferred to avoid this road were compelled to make a 45-minute detour.
To make the road safer and facilitate access to the Vercors plateau, the Drome county council decided in 2004 to build the Grands Goulets tunnel (Big Bottlenecks in French) that would offer advantages in terms of safety, economy, tourism and environment.
Up to 150 people worked on the project for four years, excavating 180,000 cubic metres of material. Bouygues TP, the contractor, first used dynamite and then opted for the MORSE system developed by Nitro Bickford, an explosive emulsion made up of ammonium nitrate, acetic acid and sodium nitrite. Click here and fr/55. View a video at www.ladrome.fr/fr/la-drome-en-videos/les-grands-goulets
Waterproofing
In tunnels, water infiltrations can cause damage to the concrete structure and induce the formation of ice stalactites. The Grands Goulets tunnel is protected against frost by a four-layer watertightness system comprising of specific materials installed between the shotcrete sprayed on the rock and the concrete formwork:
- the first layer is a brown drainage membrane that drains the ground waters to the drainage conduits,
- the second layer is a white geotextile that protects the watertightness membrane applied on the shotcrete,
- the third layer is a transparent watertightness sheet installed in 1.5 m-wide strips and welded by a double mechanical welding, that afterwards makes it possible to verify that the welds have been properly done and that the system is really waterproof,
- the fourth black layer is placed to protect the watertightness sheet from the formwork carriage that could damage it at certain places.
Therefore, infiltration waters can be collected and drained alongside the tunnel to be transported outside. This watertightness system prevents incoming water from the rock mass to seep on the roadway which can be very dangerous, especially in winter because it produces ice and stalagtites. The concrete formwork in the tunnel has a minimal thickness of 30 cm.
Safety companies
Egis Tunnels was entrusted with the design, tender documents and work supervision. The studies and electrical and mechanical works (five lots: electricity, lighting, ventilation, radio and fire protection) were commissioned to ETDE, Clemessy, Seitha and SEE RP. Visit www.groupegis.com/egis_user/References/Tunnel-des-grands-goulets,
www.etde.fr, www.clemessy.com, www.seitha.fr and www.see.fr
Escape tunnels
Thanks to the old road, it has not been necessary to bore a parallel safety tunnel. In case of emergency, rescuers will directly access to the tunnel through six transverse escapes, stretching for 800 metres altogether, connected to the old road. These escape tunnels also provide a safe shelter for the power boxes of the safety systems. The escapes are pressurised in case of fire to avoid the spread of fumes. These escapes are fitted with a lock which resists fires up to CN 90. The access doors are signalled by two columns on each side of the door, lighted by xenon lights. A specific signage has been installed on the doors and in the escapes to inform passengers. Each escape is fitted with a fire hydrant. The power is supplied by 20 kV two electrical inlets.
Speed in the tunnel is limited to 70 km/h. Sixteen safety niches are spread out at 250 m intervals along the tunnel path. Each is equipped with fire extinguishers and direct communication with the gendarmerie in Valence.
Technical rooms
There are two technical rooms in the tunnel. The upstream room manages one-third of the equipment while the central room manages the remaining two-thirds. The intervals between the rooms and the tunnel portals do not exceed 600 metres. The central room is powered from the upstream room by two high voltage lines. Each room is monitored against housebreaking and fire. The access door to the central room features a fire resistance of HCM 120. All the utilities run under the pavement.
Safety equipment
The tunnel is equipped with a fire detection thermal cable supplied by Listec. ETDE installed 70 kilometres of electrical, telecom and radio cables and will maintain the tunnel. Visit www.listec-gmbh.de
The ventilation comprises five boosters and three control stations of the atmosphere in the tunnel. The ventilation works in sanitary mode to allow users to be in a healthy environment in normal circumstances and in smoke removal mode in case of fire.
The tunnel is entirely equipped with Comatelec-branded PF5 luminaries in composite material. Threshold areas at the tunnel entrances have been dimensioned to allow good viewing of cyclists. A cycling lane has been materialised in the ascending direction.
A guidance system is installed on the lower part of the two walls and one out of five light modules is blue-coloured to signal the safety distance between two vehicles.
Supervision and communication
The Grands Goulets tunnel is one of the first tunnels to be self-managed and supervised by technological means. All is automated and dualled to enable its various users (car drivers, hauliers, cyclists and pedestrians) to drive, ride or walk through.
The incredible peculiarity of the safety system designed by Egis Tunnels and the Drome county council is the tunnel’s self-management. It complies with the risk of technical failure thanks to a powerful, dualled computer centralised management.
Sensors measure the luminosity inside the tunnel with respect to outside and adapt the lighting accordingly.
The same is true for ventilation and fire protection. Pollution sensors trigger the fans. In case of fire, other sensors, installed each eight metres, measure the exact temperature for rescuers to be informed in real time so that if a fire erupts, it can be located very accurately.
Supervision
The supervision manages all the equipment in the tunnel. The network architecture uses Schneider Electric equipment, two redundant APIs (Application Programming Interfaces) and 10 I/O islands connected to a self-healing Ethernet network. A synoptic view gathers all the important information. Eight specific displays allow to consult and command each equipment. A warning management software on the supervision server not only warns the operator about the corrective maintenance that is required but also about the monitoring that may lead to the closure of the tunnel. Visit www.schneider-electric.fr
In addition, the supervision is accessible by internet through a VPN connection. From anywhere in the Drome county, it is possible to consult in real time how the tunnel functions thanks to an internet connection.
The fire detection centre is connected both to a dry contract telephone transmitter and to the supervision server by a Modbus communication. In case a fire is detected, the tunnel is self-managed, proceeding as follows:
1. sending of a warning message to the local fire and rescue department, gendarmerie and operator.
2. automatic closure of the tunnel and access roads.
3. stop of ventilation, pressurisation of the escape crosscuts, maximum lighting in the tunnel and crosscuts and switch on of flash lights.
In case of failure of the transmitter, the warning software will send the message. This redundant principle is applied to every equipment.
In addition, a safe PABX manages part of the telecommunications. In all, four telephone lines and a GSM line can be used in the upstream room. Each communication system has a direct connection and a PABX connection.
The fire brigade premises, situated at both tunnel mouths, are equipped with a control deck. This deck is equipped with a screen monitor to view fire starts and the profile of temperature inside the tunnel. From this deck, it is also possible to activate the smoke suppression and to reopen the tunnel.
Communication
Emergency call stations have been installed at each tunnel end, in the escape crosscuts to the old road and in each safety niche. The communication system for rescuers involves:
- a radio cable for the retransmission of the radio waves in the tunnel and in the escape crosscuts.
- an interphone system installed in the fire brigade premises and in the locks of each escape crosscut. Through the PABX, an internal telephone network is installed in each technical room. Click here to view pictures and read more in French. 32-33/08.
