Hydrodemolition for renovation of historic Maastunnel 01 Mar 2018

After 75 years in operation, a large scale renovation and restoration of the historic Maastunnel in Rotterdam is underway. The immersed tube tunnel was built in the 1930s and opened to traffic in 1942. It was the first under water tunnel capable of allowing motorised transport in The Netherlands. Connecting the banks of the Nieuwe Maas, about 75,000 vehicles as well as pedestrians and up to 4,500 cyclists use the tunnel daily, making it an important part of Rotterdam's road infrastructure network.

It was at the time the time the world's first rectangular shaped immersed tube with previously immersed tubes of a circular shape. The tunnel consists of nine 60m long x 9m high x 25m wide elements. Together with access roads, the tunnel is 1,373m long with the underground part being 1,070m long. The lowest point of the tunnel is approximately 20m below sea level, with the tunnel's location easily recognised by its characteristic ventilation buildings on each side of the river.

Conjet 557 robots remove the top layer of invert concrete in the underwater tunnel

Hydrodemolition reduces noise and dust and avoids cracks in the tunnel structure while maintaining the original rebar

The twin tube tunnel consists of adjacent tubes. A 2 x 2 lane traffic tunnel and two stacked tubes alongside, one for pedestrians and the other, located on top, for cyclists and mopeds. Vehicle traffic reaches the tubes via long access roads, with pedestrians and cyclists entering their carriageways from a different location and via escalators. At one time there was a laboratory in one of the ventilation buildings to examine the air quality in the tunnel.

Over time, working stresses and humidity have taken their toll on the fabric of the Maastunnel. Some years ago tunnel experts discovered that the concrete structure had decayed. Added to this, and from 2019, the Maastunnel must comply with the latest EU laws and regulation for safety in transportation tunnels. This has led to a complete tunnel renovation being planned as the best solution to meet modern requirements of tunnel safety and to stay in service for many years to come.

Restoration of the tunnel began in July 2017, with initial work undertaken in two parts. To start, the southbound traffic lanes were closed, keeping the northbound lanes open to limit traffic congestion in Rotterdam city centre and maintain cross-river routes for emergency and rescue services. When this stage is completed, the process will be repeated for the northbound lanes.

Renovation of both northbound and southbound vehicle carriageways will take about two years and will include the replacement of the existing concrete, and the installation of new signal and ventilation systems. As the underwater tunnel possesses elements of historical significance, much of the old infrastructure, such as the spectacular cast iron ventilation system, will be restored and preserved as city monuments.

Jurjen Volmer, hydrodemolition specialist, is subcontractor to principle contractor Hompert-Renes

One essential part of the project is to renovate the 1m thick concrete floor of the tunnel, which lies 1.5m below the roadway. The existing rebar will be preserved and a top layer of between 120mm and 150mm thickness is to be removed using hydrodemolition technology and replaced with new concrete.

The first stage of the hydrodemolition process started at the beginning of September 2017 and was finished 10 weeks later. In total, some 550m³ of concrete has been removed from the 570m long x 6.8m wide concrete floor of the tunnel. As soon as the concrete top layer had been removed and the remaining rebar had been cleaned from rust, new concrete was immediately poured in place.

The concrete floor demolition was assigned to the Dutch concrete and renovation contractor Hompert-Renes BV, which is a specialist hydrodemolition company. Hydrodemolition was chosen as the most viable and efficient method of removing the deteriorated concrete and meet requirements for low levels of noise and dust emissions. Hydrodemolition will also avoid inducing cracks in the remaining part of the tunnel structure and will also clean rust from original and remaining rebar.

In-tunnel logistics temporary bridges across the leapfrogging progress of the 94 working sections

“When it comes to hydrodemolition, the work is quite ordinary since we are just removing concrete from the floor using two standard hydrodemolition robots,” says Jurjen Volmer, owner of his own hydrodemolition company, Volmer Industrial Services, which is a subcontractor to Hompert-Renes. “Working in a submerged tunnel however, sitting in the soft deposits of the river bed, is more complicated. To safeguard tunnel stability, “We have worked in 94 sections of 6m long x 6.8m wide, removing the concrete in one section, then moving 30m forward to work on the next, going back and forth in that leapfrog fashion to reach the end.”

Volmer has four operators operating two Conjet 557 hydrodemolition robots on a 24hr/day schedule and from Sundays to Thursdays. Each robot uses 280 litres of water per minute and has an operating water pressure of 1,000 bar. The other two days of the 7 day/week cycle are used for removing the demolished debris, cleaning the rebar and the concrete surfaces, and filling the work section with the new concrete.

The logistics of the operation with the confines of the tunnel environment are also quite complicated. Specially constructed bridges over working sections are required to reach other working sections and to remove the demolished concrete going forward and back again.

What has added to the successful renovation has been the use of robots for the hydrodemolition. These are becoming more common for working in tunnels and for a variety of reasons including efficiency, health and safety and overcoming laborious and repetitive work. Both contractors are long standing users of hydrodemolition equipment and loyal to the Conjet brand.