RMD Kwikform support construction of the complex 1km Hitchin Viaduct
Sian formwork has utilised a diverse range of formwork and shoring equipment from RMD Kwikform to support the construction of the complex 1km Hitchin Viaduct in Hertfordshire.
The new viaduct is a strategic part of upgrade works for the East Coast Mainline, as it will enable trains using the Cambridge line to cross over the top of four high speed tracks. Known as the Hitchin Grade Separation Project, the completion of the viaduct will remove a previous blockage, improving timetables and the speed of train journeys.
Commissioned by Network Rail, the new viaduct is being delivered by the Hitchin Alliance, a partnership between Network Rail and main contractor Hochtief. Spanning the East Coast Mainline, the construction of the curved composite steel and concrete viaduct section has been made possible thanks to a combination of expertise from Sian Formwork and RMD Kwikform.
With various challenges to overcome on the project, RMD Kwikform engineers designed numerous formwork and shoring solutions for Sian Formwork, utilising a full range of equipment. This included Minima Panels, Superslim and Alform beams, Alshor Plus and Rapidshor shoring systems, with the deck construction supported by a combination of Paraslim and Webtie composite deck formwork combined with Ultraguard edge protection. In addition to the standard equipment used on the project, to enable the casting of the crossheads and oval piers to the viaduct, RMD Kwikform designed and fabricated special steel quarter and half round shutters.
With a limited window of in which possession of the East Coast Mainline could take place, the whole programme had to be geared around the possession period. This meant that Sian Formwork had to achieve all of the preparation works in a very tight programme time. In addition, all concrete works had to be completed in an overall timeframe of just 6 months.
Commenting on the project, Hitchin Alliance project manager Julian Spiller, said: “When you are working to a dedicated date it really sharpens the focus on the project delivery. No matter what the weather or conditions we could not miss this rail possession, or the project would be put back by months. This is why we had to be 100% confident in the formwork and shoring design delivery.”
In order to meet the timescales for the project, engineers from the Hitchin Alliance, Sian Formwork and RMD Kwikform worked together to overcome some of the design challenges. Sian Formwork project manager, Ben Jenkins commented: “One of the first challenges we were faced with was how to build the oval shaped piers. Each pier varies in height and has a curved ‘bullnose’ profile at each end. We therefore needed to standardise the design and come up with a workable, fast solution that met the geometrical requirements for the whole viaduct.”
With the need to have a robust and reusable solution to cast the oval piers, RMD Kwikform engineers designed a modular ‘half round’ steel shutter system, with sections varying in height in order to make up the desired height of each pier. By combining the half rounds with Superslim, Alform beam and plywood forms for the flat pier sides, the overall oval shape was created.
Commenting on the solution, Ian Fryer, RMD Kwikform UK Engineering Director said: “With a large number of piers needing to be cast, the design team recognised that the formwork solution needed to be strong, rigid and robust. The creation of a steel faced shutter provided the stiffness and consistent dimensional accuracy needed to achieve a high quality finish demanded by the client.
Ian added: “It was the ability of the team at RMD Kwikform to quickly engineer and produce custom-made parts to compliment our range of off-the-shelf standard components, that gave Sian Formwork and the Hitchin Alliance the confidence to meet the tight deadline. Having worked with members of both teams previously on other projects it was great that they had confidence in us to provide exactly what was needed.”
Once the piers had been cast, crosshead beams were required to support the deck of the viaduct. Here Alshor Plus shoring was used to create a safe combined falsework and access platform, whilst standard Superslim and Alform shutters were teamed with custom steel quarter round formwork to form the rounded crosshead corners.
Ian: “Having cast the crosshead beams, the composite deck of the viaduct could be erected. The huge steel beams were craned into place over the East Coast Main Line, with Paraslim deck edge formwork already mounted in-situ, complete with integral debris loss prevention hoardings. Between the girders Webtie soffit formwork equipment was quickly assembled and suspended from the girder shear connectors. Both Paraslim and Webtie systems are configured with the minimum quantity of equipment giving fast erect and strip times, whilst providing an excellent soffit finish. Most importantly though, the way both systems work acts to prevent grout loss at the interface between the soffit formwork and the steel beams. This in-turn minimises the cost associated with cleaning the girder paintwork and making good.”
In addition to the formwork and shoring design, Sian Formwork needed to keep workers safe whilst working at height and to prevent any debris falling from the deck of the viaduct. Ben: “We asked RMD Kwikform to provide a safety package that would support all areas of the project. They brought in over 1km of their Ultraguard mesh edge protection equipment for the general areas, whilst designing in full height plywood hoardings into the Paraslim sections that crossed the East Coast Mainline. This was critical, as trains pass beneath the new deck at 125 miles per hour, so any possibility of debris falling had to be eliminated.”
Once opened the new viaduct will help to dramatically improve the journey times and management of the east coast rail line.