Double success for tunnel link

An important tunnelling project on the Channel Tunnel Rail Link (CTRL) has been the construction of twin tunnels linking Thameslink railway lines with the East Coast Main Line on CTRL Contract 103. The tunnels, constructed by main contractor Kier Nuttall Joint Venture (a joint venture of Kier Construction and Edmund Nuttall), are now complete and run from a point near York Way in the King's Cross area to connect with a new box for a future Thameslink station integrated within the new St Pancras station.

Each tunnel is approximately 650 metres long with a six metre internal diameter. Eight custom-designed Charcon fibre-reinforced precast segments form tunnel rings that are 300mm thick and 1 metre long. As the London clay was excavated, the smooth bore tunnel lining segments were placed at up 12 rings per shift using an automatic vacuum erector.

After each ring was positioned it was grouted using pre-blended grout manufactured by Tarmac's CMS Pozament. Approximately 4500 tonnes of Cemgrout GM grout was supplied in three different strengths to accommodate for varying ground conditions.

Designed for general grouting applications, GM grout has good pumpable qualities and has low heat hydration with minimal shrinkage characteristics.

The pre-blended grout was delivered in bulk tankers and discharged into on-site silos. The grout was mixed on the surface and dropped into a purpose designed grout car for transfer to the tunnel boring machine, ready for injection behind the rings. The advantage of using the material in bulk and discharging into on-site silos makes the grout easier to handle and contain - a major consideration in an urban environment.

Like all Tarmac CMS Pozament materials, GM tunnelling grout is manufactured under ISO 9001 conditions, which guarantees the integrity of the blending operations.

See more on Tunnelling Grouts and Caulking Materials