Carillion take advantage of a uniquely designed traveller system to keep the M6 Guardsmill extension project off the rail tracks and on the road to delivery
The design of a unique traveller system by formwork and falsework specialist, RMD Kwikform, has been instrumental in reducing the programme time for a major bridge construction on the Highways Agency sponsored £176m, 9km M6 Guardsmill expansion project near Carlisle.
Working closely with colleagues from infrastructure construction specialist, Carillion Engineering Services (CES), part of Carillion plc, RMD Kwikform engineers designed identical traveller systems to construct two six metre high, 150 metre long and one metre thick reinforced concrete supporting walls, just metres from the west coast main line.
Mounted on rails, the traveller’s allowed the concrete walls to be formed in sections with concrete poured, left to solidify and the system simply stripped from the wall and moved along to the next section, where the process was repeated.
Used to provide the supports for no fewer than 136 precast concrete beams, weighing either 37 or 56 tons, with dimensions of more than 30 metres in length and 1.36 metres in depth, the reinforced concrete walls had to be precisely formed using two specialist traveller systems. Working simultaneously over a 10 week period from June to August 2007, the traveller systems were able to reduce the overall bridge programme time construction by 10 weeks.
Using a combination of RMD Kwikform’s superslim soldiers, specialist brackets and steel beams, the main frame of the traveller system was designed to support wall formwork constructed using superslim soldiers and secondary steel beams. The 12.5 long and variable width traveller system allowed sections measuring 12 metres in length and approx 6 metre in height to be formed at any one time.
With the construction of the bridge known as Mossband spanning the busy west coast mainline, running from Glasgow to London, the design approval for both the bridge and components, including the traveller system, required input from both the Highways Agency and Network Rail. The overall design also had to overcome existing infrastructure issues, including overhead electricity cables. In order to guarantee safety the initial gantry design had to be modified to make sure it had a clearance of 3 metres from the operational rail infrastucture and could move safely along the wall.
Constructed near high voltage cables, carrying up to 25,000 volts at any one time, the whole traveller system was bonded out to protect against electrification in case of induced currents. Extra bracings and holding ties were also included in the design to protect against any adverse wind loadings.
With trains using the line every 10 -15 minutes, closing it down for any length of time to construct the walls using traditional wall formwork solutions was heavily restricted to Saturday evenings. For this reason Carillion Engineering Services and the Carillion Site team switched its specification from a standard to a traveller system, as senior engineer, Gary Muir from the Site team explained: “Having gone through the design process looking at wall formwork systems that could be taken down within the time constraints of the project, we were faced with a major dilemma. Due to the tight programme time for the project we could not afford to have any setbacks. For example if we were to use a traditional system and at any point we missed a pour, due to adverse weather conditions we would set back the construction process by a whole week.
“We therefore decided to explore other options and tasked our formwork suppliers to come up with solutions that would overcome our access issues, whilst not being over complicated or cumbersome. Having worked with RMD Kwikform before on previous projects, they were able to understand our issues and provide a system that was easy to assemble onsite but most importantly simple and effective to operate. They also helped us with the approval process, working with our team to put together presentations for both the Highways Agency and Network Rail.
“This was invaluable as we now have a system that delivers a superior grade F4 finish and is both proven and pre-approved by both organizations, putting us at a competitive advantage when it comes to future projects. We have also shared best practice within Carillion and helped our colleagues on other projects to take advantage of the system.”
In order to overcome all of the main construction obstacles and operation, the traveller solution was designed to allow the walls to be formed and struck using a simple mechanical stripping system. The main steel structure of the traveller supported the weight of the entire formwork panels, allowing them to be pulled away from the main wall to continue to hang vertically. They were then secured in place for the plywood to be cleaned and oiled, ready for it to be pushed and attached to the next section pour.
Thanks to this simple design, the typical method of stripping, involving a movement of the plywood panels though 90 degrees from vertical to horizontal, to enable cleaning, was eliminated. This had two clear advantages, firstly it removed the need for a large flat area and cranage to transport the wall formwork safely for cleaning, and secondly it reduced stresses on the plywood panels exerted by twisting movements. This in turn reduced the need for panel replacement and repair.
As each section of the wall was formed, neighboring platforms were created to allow cranes up to 800 ton to lift the concrete precast beams into place. The precise nature of the lift meant the location and dimensions of the walls had to be exactly right. Using a similarly designed traveling scaffolding system at either side of the RMD Kwikform traveller, Carillion site operatives were able to perform second fixing after the formwork was struck. Preparatory work to the reinforced steel, was also able to be conducted before the next pour commenced.
Commenting on the project and RMD Kwikform’s involvement, Robert Fox, RMD Kwikform customer services manager said: “The design of the M6 Guardsmill traveller was crucial to the success of the Mossband bridge phase of what is a 9 km long road and infrastructure project. Having had a great deal of experience globally on designing such systems, our engineering team were able to take the knowledge we have as a business to develop a solution that combined simplicity with innovation.
“However the real success of the project was the strength of support and interaction between the entire ECI project team, which was achieved by collaborative working and a customer service style approach to delivery. By working with experienced individuals from the Highways Agency, it’s ECI Contractor and the Carillion team, who were all driving for the use of innovative industry leading solutions, our engineering team were able to show how modern formwork and falsework systems can have a dramatic impact on construction projects. Not only were we able to deliver a system that provided a precise, high quality finished wall, we were also able to significantly help in reducing the overall construction time.
“With the system now approved by both the Highways Agency and Network Rail, we are looking forward to working on future projects and bringing the benefits of traveller systems to the rest of the UK construction industry.”