Ceiling mounted runway beam design helps Dunne Building Civil Engineering slide a huge sixteen tonne RMD Kwikform wall formwork system safely into place, beneath a 1.2m thick roof slab, minimising work at height inside the tight confines of the new Tyne Tunnel.
Tasked with forming the all important safety escape route on the North structure to the new £260m Tyne Tunnel project, funded jointly by concessionaire TT2 Limited and Project Promoter the Tyne and Wear Integrated Transport Authority (TWITA), specialist contractor Dunne Building & Civil Engineering has used an innovative new ceiling mounted design from RMD Kwikform to speed up the construction process.
Having prepared for the needs of the system when the roof slabs were poured using an RMD Kwikform traveller solution, special tubes were incorporated into the roof slab above the wall position and RMD Kwikform recoverable Anchor Screws either side. The Anchor Screws enabled sectional runway beams to be fixed into place, whilst the tubes allowed the concrete to be poured from above the roof slab to effect the top down wall construction. The success of the wall formwork system and its ability to allow for large escape voids to be cast in-situ, has been crucial in delivering the project to an extremely tight programme.
Appointed by TT2’s Design and Build contractor Bouygues Travaux Publics, to build the North approach structure to the new Tyne Tunnel, Dunne Civil Engineering has become the first UK contractor to combine the simultaneous use of large scale travelling wall formwork with a soffit traveller system.
Working in the tight confines of the covered tunnel section itself, complete with its 1.2m thick concrete roof, the wall formwork system, designed by formwork and falsework specialist RMD Kwikform, had to be assembled inside the tunnel and lifted into place in a very confined space.
Constructed using steel Superslim primary and Alform aluminium secondary beams with a plywood face, the eight metre tall by six metre long panel sections are almost as tall as the tunnel itself. Weighing a total of sixteen tonnes, the safe movement of the four panels along the length of the tunnel was made possible by an innovative ceiling mounted runway beam and trolley system, pulled along using a hand operated Tirfor.
Commenting on the solution devised for the escape tunnel formation, Ian Fryer, Engineering Director for RMD Kwikform UK said:
“There were two possible ways to form the walls for this essential part of the tunnel design. One was to use panel formwork with each panel needing to be manually handled into position with each use. This would have required a great deal of manhandling using mobile plant in confined spaces. A considerable amount of work at height would also have had to be undertaken.
“The alternative solution that we proposed was to mount full size formwork panels to suit the wall on beam trolleys, which would run on steel runway beams fixed to the previously cast tunnel roof slab. It was this innovative solution that ticked all of the boxes for the main contractor Bouygues Travaux Public, who specified this approach for the project.”
Once specified, RMD Kwikform engineers worked together with subcontractor Dunne Civil Engineering to understand how its staff wanted to use the system and in particular how it would sequence the individual pours. The system was then modified to further ease the changes of height of the wall, which arise as a result of the changes in roof slab height.
Using MEWPs Dunne staff were able to fix the rebar steel reinforcement into place for the wall to be formed, skilfully adding in the boxout void forms that will allow pedestrians to have easy access to the escape tunnel if an incident was to take place once the tunnel was operational.
Commenting on the project Philip Beausang, Project engineer for Dunne Building Civil Engineering said:
“Creating the dividing walls for the escape tunnel was not a simple process, as we were dealing with complex geometry. The formwork sections themselves had to be made up as parallelograms to suit the tunnel profile, whilst providing vertical construction joints to suit the reinforcement and multiple door opening box outs. A great deal of work to the initial design had to therefore be completed before we were satisfied with the solution.
“Crucial to the success of the system however was the ability for our Dunne staff to move the wall formwork along the runway beam, whilst still being able to achieve strong and secure connectivity between the two wall forms. Being able to lift the wall formwork up and down therefore was essential. Here chain pull lifts mounted between the beam trolleys and the formwork were used to effect vertical adjustment.
“When working with any solution of this type, dealing with variations in height, the gaps left between sections at the top of the formwork have to be filled in for the concrete to be poured successfully. In this case, safe access to both sides of the formwork was essential in order for any makeup required at the top of the formwork to be completed. This was achieved by cantilevering Alform beams and plywood sections.
“Because we were able to use MEWP’s to access the open side of the formwork it was the enclosed side section inside the escape tunnel, between the main outside concrete wall and inside escape tunnel wall, that required its own safe access and egress system. Here we asked RMD Kwikform to incorporate a system into the design, which they did very effectively.”
With the runway beam sections supplied in 2.4 metre units, once the wall formwork had been successfully travelled to the next section Dunne staff were able to remove sections from the trailing end and re-erect at the leading end, reducing the need for multiple sections.
With work on the escape tunnel due to be completed in just 12 weeks, the Dunne team continue to progress the concrete works for the remainder of the site, in order to meet the overall programme delivery time, that should see the North approach handed over to main contractor Bouygues Travaux Publics by December 2009.