Sustainable steel formwork for RijnlandRoute (Rhineland Route) bored tunnel access rampsIntensive cooperation for the best possible result
The construction consortium Comol5, under contract to the Province of Zuid-Holland, is working on the RijnlandRoute between Katwijk and Leiden. This new road connection, which runs via the A44 motorway to the A4, removes current bottlenecks and guarantees traffic circulation in the region. Part of the connection consists a 2,245-metre-long bored tunnel. Hendriks precon developed, produced and delivered the striking steel formwork for the bored tunnel’s access ramps.
Comol5 is a construction consortium comprising Mobilis, Croonwolter&dros, VINCI Construction Grands Projets and DEME Infra Marine Contractors that joined forces specifically for this project. The bored tunnel includes two tunnel tubes each with two traffic lanes. Ten cross-connections will be constructed between the two tunnel tubes, which in the event of a disaster can be used to escape from one tunnel tube to the other, safe tunnel tube. The tunnel will be bored 30 metres below ground level using a tunnel boring machine specifically designed for the RijnlandRoute. Access ramps are provided for on both sides of the bored tunnel. Work on the construction of the ramps is in full swing. Guy Vercruyssen of Comol5: ‘The access ramp on the A4 side is constructed in the shape of a U trench and is 300 metres long. The structured walls are poured on both sides on the loadbearing floor. A sunken trench that serves as an access ramp is located on the A44 side as well. The length of this trench is approximately 1,000 metres.’ Hendriks precon supplied three steel formwork sets for pouring the walls of the access ramps.
Sustainable steel formwork
Guy Vercruyssen had this to say about the decision to use steel formwork: ‘The average pour is 25 metres and given a total length of 2,600 metres, this means that the formwork sets are frequently reused. From a sustainability perspective, the use of steel formwork is the most attractive option. Furthermore, the project’s architect specified special requirements to be met by the finish of the walls of the access ramps. He had developed a pattern for this purpose that gives the concrete a special relief; the relief’s structure has a depth of 5 cm. With steel formwork the repeatability of this pattern is exceptionally high, while the pattern is perfectly retained during the removal of the formwork. In addition, recesses, for example for technical systems, can easily be constructed using a magnetic recess box attached to the steel formwork. The magnetic construction means we can attach the recess box precisely where the recesses are required.’
Great deal of freedom for changing heights
To translate the pattern prescribed by the architect into the formwork wall, Hendriks precon and Comol5 worked very closely together to come up with the final design. Hendriks precon’s production department managed to realise the specified precision. ‘During the preliminary phase, we spent a great deal of time working out the details. Depending on the desired pattern, the wall can now easily be assembled. The work involves formwork panels that are 2.50 metres wide. The height of the walls increases as the tunnel tube approaches and varies from 1.50 to 10 metres. Due to the changing height, the panels of different heights and the relief formation must arbitrarily seamlessly line up with each other. Furthermore, the end result complies with CUR (Centre for Civil Engineering Research and Codes) 100 Class B1 with a concrete compression strength of 50 kN/m2.’
The first 400 metres have since been poured. ‘The result is beautiful, and installing and removing the formwork goes smoothly,’ says Guy Vercruyssen. ‘The formwork is functioning to full satisfaction. Exactly as we have come to expect from Hendriks precon. Furthermore, the formwork is equipped with all of the required safety features, including two-level pouring platforms, cage ladders and lifting hooks for safely relocating the formwork by crane.’ The overall package ensures that the work can be performed as safely and efficiently as possible with a modest number of person-hours.