BAM Nuttall, Morgan Sindall, Balfour Beatty JV & KERN Tunneltechnik

The FRGCT is divided into two sections 500m and 600m. The final nominal diameter is 2.55m and minimum concrete lining thickness of 150mm. One drive has back to back S curves with a designed alignment radius of 130m, however the shutter had to be capable of 120m radius. The specific challenge was to develop a system capable of guaranteeing high production rates, comply with tight tolerances that Tideway required and ultimately ensure H&S of operatives due to the very confined nature of the work area. BMB and KERN worked jointly, to define the most suitable solution according to the complex project requirements including complete process simulations and RA. Typical full round shutters, in small diameter tunnels are usually designed with multiple shutters combined to create a long section of pour. Normally this long pour length, the concrete distribution is difficult to control which could impact the final lining quality. BMB/KERN recognised this issue and decided to develop a system composed of 4 shutters working in a hit & miss sequence. The shutters are designed to withstand full hydrostatic pressure which eliminated “rate of fill” limit in the concrete pour. This aspect provided a huge benefit in terms of programme saving, as casting requires less than 3 hours in total for all 4 shutters. Additionally, to comply with the tight curves, and ensure minimum casting thickness the shutters have been designed to be modular. They can be configured for 4m or 6m pour lengths. Resulting in a maximum overall production rate of 24m per cycle. Another key element is how the system is moved to the next location. A transport gantry was engineered to strike, move and set the formwork sections all within the confined space of the tunnel, without need for additional items of plant or equipment. Once shutters are in position, the gantry can be moved to the back of the system without interfering with the casting process. Special rail system allows to move the shutters forward without causing point loading to the fresh cast “green” concrete. Operatives can work safely inside the formwork sections. The whole system is controlled with an advanced PLC able to optimise the handling and to avoid improper use. Timber stop-end rings were designed which are pre-installed before the leading shutters are moved. All components were completely pre-assembled off-site and full-scale trials using a mock-up tunnel with segments were carried out at KERN in collaboration with BMB. Tideway and BMB attended several workshops for training and understanding the system. The shutter is currently meeting expectations, and can produce the maximum 24m of secondary lining per day even with the tight constraints of the tunnel. KERN/BMB/Tideway engaged in development from the very beginning. This ensured that one of the most innovative technical products for secondary lining, that complied with all requirements was developed. Ideas implemented on FRGCT have been used to develop the Main Tunnel system. BMB/KERN strongly believe that the lessons learnt coming from this project will become part of the future construction methodologies.

This category rewards innovation that is boosting productivity, safety or quality in the design and construction of tunnel shafts, the construction process of tunnel linings, and the excavation process of a tunnelling scheme through new products, equipment or methods. The innovative product, equipment or methodology must have been used on a specific project and be able to demonstrate benefits to the overall project outcome and have delivered greater client satisfaction.

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