When Belgian railway operator Infrabel urgently needing to repair defective concrete to a very tight schedule in the 40-year-old Biéreau tunnel just south of Brussels, hydrodemolition was selected as the only feasible rehabilitation method.
Closing the tunnel completely was not possible due to public transport demands in the urban area, and so it was decided the only option was to restore the tunnel in two sections – working and repairing the concrete from one track while trains passed by slowly on the other line. The restricted space and necessary safety and environment precautions were critical considerations for the overall renovation project, which had to be completed in just 220 days.
Restoration contractor Bageci, a regional branch of Belgian Group CFE, opted for the hydrodemolition technique, which uses extreme high-pressure water to selectively remove the defective concrete from the walls and roof. To complete the €4 million rehabilitation work, Bageci procured a Conjet Robot 365 with multipurpose arm and a specially adapted feedbeam to fit the curvature of the tunnel wall.
The 875m long, 10.5m diameter Biéreau tunnel forms part of the 4.4km long dual Line 161D railway track linking the cities of Ottignies and Louvain-la-Neuve, 34km south of the Belgian capital, Brussels. It was opened in 1975 and during its near 40 years of service, the tunnel’s concrete skin had deteriorated to such an extent that concrete sections were falling off.
A 500kW Hammelmann S1200-48 high-pressure water pump and the Conjet robot were installed on flatbed rail wagons fitted with foldable, protective walls. This allowed the hydrodemolition and restoration work to be completed on one side of the tunnel while trains could safely pass by on the opposite track.
“Due to the special safety and environmental demands and lack of space, hydrodemolition was really our only option from the very start,” said Luc Bosmans, Bageci Tunnel Project Manager. “We thought it was going to be the most productive method for this tunnel work, and it proved to be very efficient.”
In total, the Conjet Robot 365, together with the Hammelmann pump operating up to a pressure of 1,200 bar, worked 1,370 hours to selectively remove 1,610m3 of defective concrete from the tunnel circumference at an average depth of 80–100mm. The total area treated was approximately 17,000m2.
Bageci also removed concrete debris, damaged rebar, and applied new concrete to the tunnel lining. “This restoration has been completed in 220 days with the Conjet Robot demolishing and removing concrete at a rate of about 1.35m3/hr. In my opinion this is an excellent result,” said Bosmans.
“Throughout the tunnel the concrete has been harder and more resistant in some places, but with the auto regulation function, the Conjet robot selectively demolished and removed only the damaged concrete to the right depth over the entire surface,” said Sandro Bonsiambiante, Bageci Site Manager. He added: “Another advantage was the high availability of the equipment. There is a lot of environmental dust and wear and tear on equipment in this kind of application, but the spare parts supply has been excellent with no serious breakdowns.”
The Conjet Robot 365 consists of a carrier that includes pulse-monitored drive wheels, electric and hydraulic systems, and a simple, easy-to-use, control system. The carrier can be equipped with optional attachments – such as standard feed beam, tower or a rotor assembly – and can also be operated by a wireless control. The cutting head features a ±45° attack angle of the jetting lance as standard, variable oscillation width, and encoders for lance turning and cradle position.