Construction Enquirer News Fibre optic technology senses minute ground movements

Latest fibre optic technology on an HS2 construction site can sense minute ground movements in embankments and cuttings and could help prevent land slips and detect the formation of sink holes.

The project’s Chilterns tunnel south portal site is the testing ground for the “Sensorgrid” system developed by the University of Cambridge’s Centre for Smart Infrastructure & Construction (CSIC) and geosynthetics manufacturer HUESKER.

The standard ground-stabilizing mesh woven with fibre optic cables is being used by contractor Align, its designer Jacobs and infrastructure monitoring company Epsimon Ltd on a test pit at the site to simulate ground movement.

Heavy-duty water-filled bags were laid in the base of the pit, sections of Sensorgrid were laid over it and then buried. Monitoring equipment then generated pulses of light that travelled through the fibre optic cable.

To simulate ground movement, water was released from the bags causing the weight of the ground above to move and strain the mesh which in turn causes a change in characteristics of the light pulsing through it.

The successful trial showed that Sensorgrid can detect small ground movements earlier and more effectively than established ground monitoring techniques.

The team estimates that on construction costs alone, proactive preventive action enabled by Sensorgrid would be up to 10 times less than the cost of repairing ground that has failed. The benefits of disruption reduced or avoided would be in addition to this saving.

The technology is now undergoing a full scale live trial elsewhere at HS2’s South Portal site near the M25 motorway. Two kilometres of Sensorgrid has been incorporated into a cutting for the railway. It will provide continuous data to the monitoring team over the next two years.

HS2 Ltd innovation manager Rob Cairns said: “Sensorgrid is a great example of how we’re leveraging HS2’s size and scale to draw on British expertise to develop a technology and demonstrate its innovative capability in the early stages of construction. This will act as a test bed for proving out significant benefit to the operational railway, with long term benefits in bolstering the resilience of the UK’s transport network.”

Align’s innovation manager, Nick Podevyn said: “A lot of hard work has gone into this innovation, which has been in incubation for more than a year. It has been an exemplar of open collaboration and working as one team to deliver the solution. It’s fantastic to see the prototype being physically tested on our site and then the technology being implemented on the live project.”

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