For formwork and falsework specialist RMD Kwikform, given 7 days to go back to the drawing board, following an unsuccessful bid for an important contract on the Tyne Tunnel, led to the conception of the company’s most innovative travelling tunnel soffit support system to date.
Having secured the deal through Concessionaire TT2's main Design and Build Contractor Bouygues Travaux Publics at the final hour, engineers teamed up with North tunnel section subcontractor, Dunne Building & Civil Engineering, combining expertise to successfully utilise the unique traveller system.
Travelling on the equivalent of train tracks, the RMD Kwikform traveller used a combination of specially designed and standard equipment to create a solid yet flexible structure, capable of snaking up an incline of 6%. Withstanding loads of up to 750 tonnes the traveller was capable of supporting up to 300 cubic metres of concrete poured over 173 square metres.
The 21m long traveller system was used by Dunne Civil Engineering to successfully cast the nine, 1200mm thick roof slabs that make up the roof of the tunnel’s North section for the Tyne Tunnel operator, TT2 who, together with Project Promoter the Tyne and Wear Integrated Transport Authority (TWITA), funded £260m project.
For RMD Kwikform Engineering Director, Ian Fryer who led the four strong engineering design team for the project, overcoming the challenges faced at both the design and utilisation stages of the project were particularly rewarding.
Ian said: "When you are challenged to go back to the drawing board on a project of this scale and importance, it tests all of your engineering knowledge and capabilities.
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"The challenge was to deliver a whole-slab-area travelling formwork system with 2 metre height variation which could be operated without the site staff working at height. The traveller also needed to give the users the flexibility to snake the equipment up an incline of 6%, travelling on rails whilst casting a slab that was up to 8.5 metres off the ground, at the bottom of a 25 metre deep excavation full of large ground shoring props.
"Once we had overcome the design element and been awarded the contract by Bouygues Travaux Publics, we entered the phase of taking the proposal design to the end solution. At this time, because the works for the North contract were subcontracted to Dunne Civil Engineering, we had to deal with a new construction team to demonstrate how the system would work.
"At this stage Dunne's were able to assist the design team with suggested amends to the design in order for the system to best meet the needs of the site team. The very tight programme schedule also placed further challenges on the delivery and erection of equipment, which physically required assembling and commissioning 60 tonnes of system and special components at the base of what is effectively a large hole.
"As part of the intensive design and detailing phase that followed, the first thing the team concentrated on was the calculations, detailing, procurement and fabrication of the special items of equipment needed for the project. Shortly followed by production of the general arrangement drawings required for assembly and the detailed instructions for use of the machine.
"Procurement of the special equipment, (which included the hydraulic leg components that were central to the function of the traveller), ultimately determined whether the system could be assembled and operated within the time frame required."
Having developed an assembly sequence in collaboration with Dunne’s for the traveller, RMD Kwikform provided three customer service team members to assist with the erection of the traveller which as a part of the design required the support legs to always be perpendicular to the slope of the soffit.
Unlike previous travellers designed by RMD Kwikform, which incorporated structural steel work at the soffit level, the RMD Kwikform engineering team recognised the opportunity to adapt its R700 truss girder panels for use on this project. By adapting the R700 girders with specially fabricated cantilever frames at the ends, the units were used to span across the tunnel whilst still maintaining sufficient headroom beneath to accommodate site traffic, such as concrete mixers and scissor lifts.
Having to negotiate both varying horizontal and vertical curves, the 21 metre long traveller had to be flexible enough to be able to be travelled around the tunnel profile, rising from its start point at the river side end wall. For this reason RMD Kwikform split the structure into three 7.2m long rectangular tables, which were linked by adjustable bays of equipment that could be changed in length to adjust the horizontal and vertical curvature of the entire assembly and provided sufficient flexibility during travelling to accommodate level tolerances in the running rails.
Advancing up to 21 metres in about an hour, the RMD Kwikform traveller system has reduced the time for slab pouring significantly when compared with traditional methods. This in-turn allowed this section of the project to be completed on-schedule by the end of November 2009.
For further information contact RMD Kwikform on Tel: 01922 743743 or Email: info@rmdkwikform.com
