Drivers who regularly use the Grouft tunnel on the A7 will need to remain patient a little longer.
Work has been under way in the tunnel for several months. For the past six months, the overtaking lane has been closed in both directions and the speed limit reduced to 70km/h after signs of material fatigue were discovered in the tunnel's 32 ceiling-mounted ventilation fans.
The new custom-made fan blades have now finally been delivered, allowing replacement work to begin this week.
Christian Ewert, technical tunnel manager at the National Roads Administration, explained that small cracks caused by material fatigue had been detected in the fans. Replacing the fan impellers is therefore the immediate priority, he said.
However, he noted that as each fan has to be removed, the opportunity is also being used to carry out a major overhaul of its motor. "The motors are opened up and the ball bearings inside are replaced", he said, adding that all oil and grease lines are also being renewed.
Brake dust, carbon monoxide, road salt, and microscopic cracks have all taken their toll on the fan blades, which each weigh more than 100kg, over the past ten years. The fans are now being refurbished in pairs, six days a week, with teams working in two shifts.
The current high temperatures have made the work even more difficult for employees of the two companies involved, one from the UK and the other from Luxembourg. On Friday, the heat distorted one of the shafts so severely that it had to be cooled before the blade could be fitted.
According to Ewert, the fans are primarily intended for emergencies, particularly to extract smoke in the event of a fire. They are also used for routine ventilation when the tunnel's sensors detect pollution, he said.
"If a car with a faulty catalytic converter drives through and produces smoke, that is detected", he explained. Visibility and carbon monoxide levels are continuously monitored, and two or four fans are then activated to remove the pollution, according to Ewert.
Since the 2,966-metre Grouft tunnel opened to traffic in 2015, five fires have been recorded.
Ewert stated that once a fan has been serviced during the day and is ready to be reinstalled, it is lifted back into place at night. The installation team secures it to the existing ceiling frame before a series of final checks are carried out, he explained.
"We test the vibrations along three different axes", he added. The fan's direction of rotation is also checked before it can be approved and returned to normal operation, according to Ewert.
Attaching each one-tonne fan to the ceiling mountings requires considerable care and precision. The operator below in the telehandler and the two workers in the elevated platform beneath the ceiling have now become a well-coordinated team.
Each night, two fans are reinstalled and another two are removed. Work is currently taking place in the northbound tunnel.
Provided everything remains on schedule, the tunnel should be fully reopened to traffic before the construction sector's collective summer holiday. This will come as welcome news to the approximately 33,000 motorists who use the tunnel every day and have frequently faced congestion in recent months.
Until then, however, further patience will be required. One direction will continue to be closed overnight from Monday to Saturday until all the fans have been replaced.
