Doka selected for specialised formwork solution for HS2

Formwork solutions provider Doka is supplying equipment and expertise for UK-based project HS2 to ensure the completion of a ventilation shaft. The rail link project is set to revolutionise rail travel between London and cities throughout the Midlands, northern England and Scotland in the UK.

The concrete casting process was further complicated by three large tunnel openings (Photo: Doka)

For the project, Doka was selected to supply a specialised formwork solution for the construction of the shaft secondary lining to the Victoria Road Ancillary Shaft. This section of works is being carried out by Skanska, Costain and Strabag Joint Venture (SCS JV).

Precast rings partially form the Ancillary Shaft at Victoria Road, the lower section of the shaft’s wall is also concrete-lined. This aspect of the shaft’s composition is said to have required the ingenuity of Doka’s formwork solutions to ensure a failproof installation. Doka added that it was particularly crucial to casting the shaft’s secondary lining which was backed by a waterproof membrane.

Ideal solution to casting conundrum

Due to the shaft’s 25.1m diameter, the secondary lining was cast in five separate pours to approximately 15m above the base slab. Securing the formwork and climbing platforms without perforating the waterproofing during the casting process was one of the many challenges given to Doka. 

Featuring brackets that adapt quickly to both inclined and radiused walls, Doka’s D22 system was used to allow for forming casting concrete without the need for ties. This eliminates the risk of puncturing a wall’s waterproofing. The D22 system’s success can also be attributed to Doka’s technical team carrying out the necessary complex calculations to maintain concrete pressures and deflection tolerances.

The concrete casting process was further complicated by three large tunnel openings. Designed for the train tunnel intersections, these significant openings provided an additional challenge as there were no previous walls to attach the D22 platforms. This issue was overcome with Doka’s Staxo 100 shoring system, an adaptable, easy-assembly load-bearing tower that allows the economical shoring of floor slabs of widely differing layouts.

All-round service benefits

Doka’s Concremote system was also used in the project (Photo: Doka)

For projects in busy, congested areas such as central London, space is at a premium. Doka says that they were also able to overcome this issue, thanks to its “ready to use” pre-assembled panels and platforms which reduce space requirements on site.

Furthermore, the company’s all-round service provision was supplemented by its onsite support, with Doka’s site demonstrator making regular visits to advise the installing contractor, SCS JV, on aspects of its formwork and jump system operation. 

Doka’s Concremote system was also used in the project. The concrete monitoring device uses sensors to measure the temperature and calculate the compressive strength of the concrete structure and helped by ensuring the next cycle could be planned and started with increased accuracy and confidence.