WAGON WHEEL FORMWORK IS JUST THE TICKET FOR CROSSRAIL TOTTENHAM COURT ROAD STATION
Tasked with forming four collars for tunnel openings, of up to 9.45 metres wide, at the Tottenham Court Road Crossrail station; contractor Laing O’Rourke turned to engineers from formwork specialist RMD Kwikform, to design a bespoke solution for this challenging part of the project.
Laing O’Rourke required a lightweight solution to support the creation of four different sized circular concrete tunnel collars to very tight tolerances. The solution itself also had to be strong enough to be assembled on the ground horizontally, rotated through 90o, and lifted down vertically into the underground ticket hall.
Commenting on the project, Laing O’Rourke project engineer, Alex Fleming said:
“Getting this part of the project right was extremely important, as we were forming the start of the inner tunnel lining. We needed to ensure that the four, two metre wide tunnel openings were designed with the project environment in mind. The challenge was how to design a circular collar solution that was relatively lightweight, and could be manoeuvred into place in a confined area, with restricted craneage.”
RMD Kwikform design engineers had to take into account the methodology of construction when designing the solution. The wagon wheel had to be fully assembled flat on the ground to ensure all components fitted correctly. Once completed as a whole unit, the site team split each wheel into three sections, determined by weight. These sections were then rotated 90 degrees to stand up vertically. Using a mini crane, the three sections were lifted into position in the underground ticket hall, carefully avoiding the shoring props above.
Alex Fleming continues:
“Working with the RMD Kwikform engineering team, we were able to analyse the proposed model and method of construction, which enabled the complicated collars to be cast in two pours. In practical terms, the wagon wheels formed the structural support to what were effectively large circular box outs in substantial single sided wall pours. Once inserted into the tunnel, the concrete could be poured in a carefully controlled manner between the shutters and the pre-existing end wall of the station box, thus forming the collar.”
As part of the design process, RMD Kwikform engineers worked with expanded polystyrene (EPS) specialist Cordek, to form the outer circular aspect of the formwork, which was then supported with a steel Slimshor frame. The frame and Cordek sections had to be able to connect securely together, so the dimensional accuracy of the frame was extremely important. Made up of steel Superslim soldiers and props, the flexibility and rigidity of the design enabled the circular outer frame to be supported uniformly, whilst allowing it to be readily struck and removed once the pour was completed and cured.
Commenting on the project, RMD Kwikform sales representative Tom Day, said:
“This is one of the more interesting formwork challenges we have had on Crossrail projects to date; it shows just how important it is to engineer solutions capable of millimetre accuracy. It was critical we got this right first time. Forming a perfect circle is a challenge at the best of times, let alone when the circle is in the vertical plane; taking into account its size and location, 30 metres below ground.”
