Team Tarmac meets Lea Valley Cable Tunnel Challenge
15th May 2007
Products from Tarmac Precast and Tarmac CMS Pozament have played an important role in the completion of two underground cable tunnels, which will carry power and communication lines needed for the redevelopment of Lower Lea Valley. This cable tunnel project is the first job to be commissioned as part of the redevelopment of east London ready for 2012.
Contractor J Murphy & Sons selected Tarmac to supply the bespoke tunnel linings as well as a specialist tunnelling grout. The £230 million project comprised two 6km precast concrete tunnels running between substations in Hackney and West Ham. Construction of the tunnels and a series of shafts enabled lines to be placed underground rather than overhead, freeing up around 40 hectares of land for further development.
Tarmac Precast manufactured and delivered over 67,000 Charcon tunnel segments made from a concrete mix that included polypropylene fibres to reach a compressive strength of 60 N/mm2 at 28 days. The segments were used to create 6,000 rings for a smaller 2.82 metre diameter EDF Energy tunnel and 4,300 rings for a 4.15 metre diameter National Grid tunnel. Tarmac Precast also supplied shaft rings for eight shafts, ranging in diameter from six to 15 metres.
Each precast ring was grouted using GM 5 pre-blended grout from Tarmac CMS Pozament. Designed for general-purpose applications, GM 5 grout offers good pumpable qualities and minimal shrinkage. More than 10,000 tonnes of grout was delivered, mostly in bulk road tankers. Kevin McManus, Murphy’s Tunnelling Manager for the project, said: ”Our tunnelling engineers were able to consistently achieve exceptional production rates. With the concrete rings being erected and grouted immediately behind the tunnel borers, it was vitally important that Tarmac’s products matched specification and were delivered on-time’’.
Since the four tunnel boring machines began tunnelling operations in June 2006, Tarmac’s products have helped Murphy engineers to reach production rates of up to 60 rings per day. The main tunnelling work was completed, on schedule, in April 2007
Tarmac Precast’s commercial manager, Marcus Parnham, commented: ‘Our specialist knowledge in manufacturing bespoke linings meant that we were able to formulate a specialised concrete mix and cast segments that met Murphy’s specific needs for the contract’’. Bryan Smith of Tarmac CMS Pozament added: ‘’Our task was to factory blend quality assured tunnelling grout and provide fast and efficient bulk deliveries to meet Murphy’s strict schedule’’.
Tarmac has already secured another order for a further tunnel in the Lower Lea Valley, known as the Bow Extension, which is 1km long. This tunnel is a spur from the EDF Energy tunnel, and will comprise 835 rings at 2.82 metre diameter, as well as segmental linings for two shafts of 7.5 and 10.5 metre diameters. Again, the rings will be grouted using Tarmac CMS Pozament grout.
