London, UK
Crossrail is one of the biggest transport infrastructure challenges ever encountered in the UK.
Stretching across London – and featuring the building of stations in some of the most densely populated places in the world – the project has pushed designers and engineers towards constant innovation. Tottenham Court Road Crossrail station is set to be one of the most prestigious achievements of the project.
Tasked with forming four collars for tunnel openings of up to 9.45 metres wide at the station, contractor Laing O’Rourke turned to engineers from RMD Kwikform to design a bespoke solution for this challenging part of the project.
The contractor 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 90 degrees and lifted down vertically into the underground ticket hall.
When they were designing the solution, our design engineers had to take the methodology of construction into account. 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.
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 cranage.
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.
Location
Application
Collars for tunnel openings at Tottenham Court Road Station
Challenge
The solution had to be strong enough to be assembled on the ground horizontally, rotated through 90 degrees and lifted down vertically. Restricted cranage in the area meant lightweight components were essential. Forming had to be a perfect circle with no time or room for error.
Solution
Formwork
Products used
As part of the design process, our 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 while 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.”