RMD Kwikform has revealed a bespoke wagon wheel formwork for Crossrail tunnel openings.
Formwork specialist RMD Kwikform has designed four bespoke collars for tunnel openings for Tottenham Court Road station.
Contractor Laing O’Rourke required a lightweight solution to support different sized circular concrete tunnel collars to very tight tolerances.The collars needed to be strong enough to be assembled on the ground horizontally, rotated through 90o, and lifted down vertically into the underground ticket hall.
Laing O’Rourke project engineer Alex Fleming explained: “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.
Once completed as a whole unit, each wheel was split into three sections and then rotated 90 degrees to stand vertically. The three sections were then lifted into position in the underground ticket hall.
“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,” explained Fleming. “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.”
RMD Kwikform sales representative Tom Day said it was one of the more interesting formwork challenges encountered on Crossrail projects to date. “It shows just how important it is to engineer solutions capable of millimetre accuracy,” he said. “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, 30m below ground.”
Crossrail is working with Transport for London on the £1bn transformation of Tottenham Court Road Station. It is expected to open in 2018 with a new station building the length of three football pitches, four storeys underground. The new ticket hall will be constructed at Dean Street, with the station box continuing five levels below ground at a depth of around 25m, providing access to the new Crossrail platforms.