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Frogmore Connection Tunnel

Location: London - UK
Customer: BMB JV
Working years: 2020 - 2021
Project information:
Supplied equipments: The Frogmore Secondary Lining Shutter is an innovative system developed to comply with the challenging design of the Frogomore connection tunnel and the tight tolerances.

The Frogmore Connection Tunnel is divided into two sections 500m and 600m long. The final nominal diameter is 2.55m with a concrete lining thickness of 150mm.
Especially one drive has curves with a minimum radius of 120m.

The specific challenge was to develop a system capable to guarantee a high production rate, to comply with the tight tolerances and to ensure H&S in a confined workspace.

KERN developed a system composed of 4 tunnel formworks working with in a hit & miss sequence. The structure is designed to withstand full hydrostatic pressure with no limit in the concrete filling time. This aspect provided a huge benefit in terms of programme since the casting requires less than 3 hours in total for all 4 shutters.

In order to comply with the curve radius and to ensure the minimum casting thickness the shutters have been designed to be modular. They can be configured for a 4m pour length or either for 6m. The result is that an overall production rate of 24m per day is achieved.

Another key aspect of the project is the shutter advancement. A transport gantry has been engineered to strike, move and set the formwork sections in a confined space. Once the shutters are in position, the gantry can be moved and parked at the back of the system without interfering with the casting process. A special rail system allows to move the shutters forward without overloading the young concrete. The operatives can work safely inside the formwork sections.

The four formworks and the transport gantry are controlled with an advanced PLC able to optimise the handling and to avoid improper use.

Special timber stop-end rings have been designed which are pre-installed before the leading shutters are moved. The machines were completely pre-assembled off-site and a full-scale trials using a mock-up with tunnel segments were carried out at KERN premises in collaboration with BMB. Tideway and BMB attended several workshops implementing the solution and trainining the staff.

Additional Services: Machine installation , Machine Transformations , Machine Removal , Supervision ,