RMD Kwikform has created an innovative travelling tunnel soffit support system, 21 metres long and weighing 60 tonne, to assist with the casting of the roof slabs in the tunnel's North section. The firm was given just seven days to go back to the drawing board and create the system, following an unsuccessful earlier bid.
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.
ADVERTISEMENTTravelling 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.
As of October 26th 2009, the 21m long traveller system has been used by Dunne Civil Engineering to successfully cast six of the of 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: “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.
“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.
Commenting on the soffit pours and the traveller system Philip Beausang, Project engineer for Dunne Building & Civil Engineering said: “Whereas the base slab rises at a continuous 6% incline, the height of the tunnel changes multiple times throughout its length, so at some time the soffit slopes by up to 12%.
“With all the challenges we faced on the project, it was actually the very first pour that had the most severe soffit slope. We were therefore tasked with setting up a unique never-before-used system in the hardest possible arrangement!
“We had just three weeks to complete the assembly and commissioning phase of the project and were pleased to have the support of three of RMD Kwikform’s customer service team for this phase and for subsequent coarse level adjustments.
“Although we had a challenging start to the project, by working through the early stages with RMD Kwikform, our team were able to carry out all of the required operations without the need for further assistance. As we have grown in confidence with the system, we have been able to benefit from the speed and simplicity the traveller offers us and have been impressed with its performance.”
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.
Ian: “In using the R700 girders this had the effect of simplifying and speeding up detailing, whilst increasing the proportion of standard hire equipment of the traveller, making it commercially more attractive to Bouygues and Dunne. Having said this, the special parts that had to be added to the R700 girders were challenging within themselves.
“The tunnel is being constructed between deep diaphragm walls and due to the tolerances in the vertical alignment of these walls, the width of the tunnel structure can vary significantly. What this meant in layman’s terms was the design of the traveller had to be such that it could accommodate a width of tunnel soffit varying by a maximum of plus or minus 600mm.
“In order to accommodate this, sliding sections of formwork were developed and incorporated into the special cantilever frames, which were then attached to the ends of the R700 girders. These frames also acted to connect the R700 girders to the supporting Megashor and special telescopic legs.”
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.
Ian: “Each of the three tables was mounted on four robust double flanged wheel units that could be lowered onto the rails which were themselves anchored to the base slab. Crucial to the whole travelling operation, the wheel units were designed so that the wheel could slide on an extended greased axle. This enabled the traveller to accommodate small changes of direction in the facetted rails to smoothly negotiate the tunnel curves.
“Each of the four wheel units was attached to the main Megashor leg, with each table having six legs in total. In order for the required level adjustments to be made the two legs at the centre of each table were equipped with specially designed hydraulic telescopic leg units. Using hydraulic power packs the legs are capable of changing the height of the traveller by up to two metres, lifting the whole table off the ground to facilitate traveller height adjustments, without any need to work at height.
“Once the traveller is lowered onto the rails, the whole unit can be advanced by simply using a pair of three tonne hydraulic Tirfor units attached to the front of the traveller legs using standard equipment.”
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 has allowed this section of the project to be on-schedule for completion by the end of November 2009.
Additional Technical InformationIan “ The most labour intensive part of the project was dealing with course level adjustment. This refers to a section of tunnel where the level of the soffit has to change, either upwards or downwards. In this case the use of the six hydraulic legs, one set on each of the three table sections played an important role.
“Once the traveller is struck by taking the pressure off the Megashor jacks, the specific Megashor legs that require adjustment can be dismantled by simply raising the hydraulic rams to relieve the load. Because Megashor is a standard RMD Kwikform product, there are a range of standard leg length sections from as small as 90mm that can be used to adjust the size of each leg, with the Megashor jack allowing for fine adjustment.
“Once the pressure is removed from the leg it is a simple process of removing four pins in each leg that help fix it to length. These pins can then be driven out and the rams activated to raise the equipment to the correct level. The pins can then be reinserted through the leg sections and the four non telescopic Megashor legs on each table can then be adjusted manually.
“With each pour section mapped out on a programme schedule the Dunne’s team were able to refer to detailed support drawings and guidance notes for the whole process."
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