Innovation Showcase

Constructing Tideway’s largest shaft at Kirtling Street.

The Kirtling Street shaft on London’s Tideway super sewer project has a diameter of 30m, making it larger than any other across the entire Tideway project. Peri’s engineering team worked collaboratively with the Ferrovial Laing O’Rourke JV (FLO) site team to deliver a temporary works solution for two tunnel portals at the base of the shaft that were 7.3m wide and 6.5m deep in addition to a 1m thick secondary lining for the shaft walls.

The tunnel portals had to be cast in tandem with the tunnel drum but the 15m height of the portals made the formwork requirement more challenging. To ensure timely and simultaneous delivery of these structures, Peri’s engineers proposed an innovative solution comprising standard rentable components from its Variokit range, minimising costs and maximising reusability.

The proposed formwork solution split the concreting process into two halves to accommodate the height of the portal. For the lower half, the tunnel drum was integrated with a moving frame used in conjunction with SB brace frames. The top half comprised SB brace frames which were integrated with Peri Up heavy duty shoring.

To support and keep the SB brace frame securely in position, anchors were cast into the concrete structure at 45°.

The drum formwork was integrated with heavy duty trusses comprising RCS rail frames and heavy duty rollers to facilitate movement. This efficient solution was designed to serve multiple purposes, such as enabling safe installation into the casting position, height adjustment and preventing uplift during concreting. It also facilitated the safe removal of the formwork unit out of the shaft.

Minimising cost and waste were important considerations of the design. The flexibility of Variokit components and cost-effective design ensured that the same solution could be reused for the second tunnel entrance.

For the secondary lining, the FLO site team required an efficient jump form system that would reduce cycle times. Peri’s engineers evolved the solution they had previously designed and delivered at Tideway’s Blackfriars site to accommodate the larger diameter of this shaft.

This comprised a hybrid rail-guided climbing system (RCS) and a single-sided climbing system (SCS), which enabled faster cycles as all platforms climbed simultaneously with the support of RCS Max hydraulics.

Hydraulic operations accelerated the circumferential lift as the system could be jumped in just one to two hours compared to crane operation which took 30 minutes per platform. This also enabled the crane to be used for removing locomotives from the shaft, making hook time more efficient.

The SCS climbing system was used to support the concrete load from the single-sided pours. RCS Max lifted the entire ring comprising 41 formworkplatforms to the next level in 3.2m lifts with the push of two buttons. In addition to faster cycling, RCS Max provided built-in leading edge protection, an important safety provision as formwork units climbed seamlessly without needing to be repositioned at each level. Peri’s engineers also incorporated a bespoke shoe adapter to maximise the width of influence and to support the specified concrete pressure, which resulted in an anchor load of 200kN.

Safe access to the shaft walls was efficiently integrated into the climbing formwork design by extending the platform above the casting level. Sufficient space was created on the platform to accommodate a four person man rider, which was used to transport workers to and from various levels inside the 50m deep shaft.

The entire solution was fabricated offsite in Peri’s Rugby depot, contributing to time savings, reductions in labour and lower on-site safety risks.

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