Formwork and ground shoring provider RMD Kwikform supported the construction of two shafts on the Tideway project.

The shafts at King George’s Park and Dormay Street are part of the western section of the Thames Tideway Tunnel scheme.

Construction of the 7km west section is being delivered by the Bam Nuttall, Morgan Sindall and Balfour Beatty (BMB) joint venture.

RMD Kwikform (RMDK) supplied temporary works solutions to form concrete elements on all aspects of the shafts. It was awarded the works in February 2020, and its involvement in the project ended at the start of this year.

Work at Dormay Street involved connecting the existing local combined sewer overflow (CSO) to the main tunnel. The site has also been used to drive the Frogmore Connection Tunnel southwards to King George’s Park and northwards to Carnwath Road Riverside.

The King George’s Park site is the start of the Frogmore Connection Tunnel, which will link sewer overflows into the main tunnel.

One of the key challenges of this part of the project was to ensure all the structures within these shafts could be built simultaneously. The temporary works solutions needed to accommodate all the different construction processes underway at each level.

RMDK achieved the linings of both shafts through slipform construction. It supplied formwork for the surface and internal shaft structures, and these incorporated the temporary works structures needed to withstand demolition and breaking during the works.

The range of temporary works systems supplied included RMDK’s Alshor, Rapidshor and Megashor falsework solutions, Superslim Soldier primary formwork beams, aluminium beams, Maxima wall formwork panels, and Trapeze panels for curved wall formwork.

RMDK supported the delivery of the project with 3D modelling due to the complex geometry of some of the structures. It said that the sharing of 3D models enabled early intervention to prevent materials from clashing in the interface between the permanent and temporary works.

BMB said that access to a dedicated senior engineer from RMDK, capable of supplying both 2D and 3D drawings, was key to the successful completion of both sites’ shafts, reducing design time and ensuring the construction programme for both sites remained on track.

At both sites, vortex drop pipe structures will intercept existing spills into the Thames and transport the discharged effluent vertically down through CSO drop shafts to the newly constructed tunnels.

One critical aspect of this construction process involved the breaking out of the vortex safety grill chamber, which controls the flow of sewage and wastewater into the tunnel. Here, five separate levels of concrete had to be cut, slid out and then removed safely from the shaft. All this work had to be undertaken while avoiding the surrounding ground shoring props.

BMB’s Dormay Street and King George’s Park site agent Amy Hogg said: “Both shafts were incredibly complex in terms of the civil engineering that had to be delivered within them. The biggest challenge was installing the vortex drop tubes – these huge stainless steel tubes fill approximately two-thirds of the shaft. Building the temporary works that would support the weight of these tubes and keep them in position, as well as enabling the build of all the structures around it, was quite a complicated process.

“For instance, the vortex drop tube and generator for the Dormay Street site is quite unique, as it sits partly within the shaft, and partly outside of it. This was a complex interface, and we required a temporary works design that could meet these demands. As this part of the project progressed, quite a few changes and adaptations were needed, but RMDK helped make the temporary works design for this build a reality.”

The £4.2bn Thames Tideway Tunnel scheme involves the construction of a 25km long “super sewer” to intercept, store and ultimately transfer sewage waste away from the River Thames.

RMDK also provided a heavy-duty propping system for Tideway’s Chelsea Embankment Foreshore site.

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