Costain and the Cambridge Centre for Smart Infrastructure and Construction (CCISC) at Cambridge University are working on a new initiative for National Grid’s London Power Tunnels (LPT) project that could make construction of a tunnel with concrete segmental linings more efficient.

The LPT project involves carving out 32km of tunnels under the capital to help ensure Londoners keep on enjoying safe and reliable electricity supplies decades into the future.

Costain approached the CCISC to investigate possible innovations that could be used on the project. The use of optical fibres that could be embedded within the concrete tunnel segments to measure axial and bending strain levels of the tunnel lining in a distributed manner emerged as the innovation with greatest potential.

-- Advertisement --

These instruments would be used to collect data that would help the university researchers understand how tunnel linings perform during and after construction, with the aim of using these measurements to assess potential efficiency savings in construction of the tunnel segments.

Six pre-cast, steel fibre-reinforced concrete segments bolted together form a tunnel ring, which in turn forms the tunnel lining.

With the segments for one of the four-metre diameter tunnels currently being dug for the LPT project 250mm thick, any viable reduction in their thickness indicated by the sensors could save thousands of cubic metres of concrete over the course of a major contract, together with a corresponding reduction in the amount of ground material to be removed.

LPT project team members are working with the CCISC on a trial of the new distributed optical fibre strain measurement system. The optical fibre sensors were cast into the centre of the segments in February and are being installed this spring on the tunnel drive between Eade Road to St John’s Wood in northwest London. Further instrumented sections will be installed on another section of the route, between Eade Road and Hackney, east London.

Data will be collected over a 12 to 18-month period and analysed to see if redesigning the sections would bring efficiency savings.

(CD)