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Extending the GBN to Hinxton Genome Campus

The Granta Backbone Network (GBN) is the collegiate university’s privately owned fibre optic network. The decision was taken in 2018 to extend the network to Babraham Institute and Wellcome Sanger Institute (Hinxton) to enable greater collaboration between institutions.

Extending the GBN into rural Cambridgeshire

The existing 60kms of GBN have been installed in urban areas, using the traditional industry standard method of laying 90mm duct, which allows fibre optic cables to be manually pulled through. However, Babraham and Hinxton are situated several kilometres outside the city boundary in a very rural location. This change in circumstance allowed other methods of implementation and technologies to be explored.

Mole ploughing

Mole ploughing is not a new technique, however this is the first time it's been done in Cambridgeshire. Farmers and groundsman have been using it for many years to help drain land. More recently though it has been adapted for use by telecoms companies to quickly and cheaply install ducting in soft verge. Mole ploughing works by cutting a slit in the earth and forcing down continuous narrow honeycombed duct, which transport the fibre optic cables.

The mole plough technique lets us install several hundred metres of duct work per day in suitable conditions, with minimal disturbance to the surface of the verge. Once the duct is installed and the mounded soil smoothed, the verge flora does not need to re-establish and the streetscape recovers almost immediately.

Footage of the duct being laid along the A505, between Babraham and Hinxton. What previously would have taken 3-4 days, took around 2 hours.

Directional drilling & stitching

Directional drilling is another new method we are using to speed-up works. For this project, it was first used to pass under the Gog Magog Roundabout, avoiding disruption to traffic and costly traffic management measures. The same directional drill rig was also used to carry out a 'drill and stitch' along Babraham High St, where no soft verge was available.

A mobile rig is set up next to a small hole and a drill head is fed down the hole, to which 4.5m sections are attached. Depending on conditions, this machine can span roughly 150m and is completely controllable in all directions.

This method involves a series of directional drills 140m apart. The rig drills from pit to pit, forming a stitching effect. The duct, which is coiled on a large drum, is then attached to the end of the drill and pulled back through all the holes. The drilled duct is between 1.2m and 2.2m below the surface, thereby avoiding established tree roots and other utilities’ underground plant.

The 'drill and stitch' method is used where we need to lay ducting under hard surfaces to avoid disruption to traffic and costly traffic management measures.

Blown fibre

The honeycombed nature of the microduct being laid will use blown fibre, whereby a mechanism uses compressed air to form a pocket of air around the fibre cable, creating low resistance. The machine then pushing the fibre through the micro duct, which is far less labour intensive then manually pulling cables.

GBN microducting cross-section

GBN microducting conduit

Programme of works

The project is three months into the five month programme and is on schedule to complete in late March. The biggest risk will be to cross two high pressure gas mains, which needs to be coordinated with Cadent.

En route, strategic fibre-optic joint locations are planned, so that future connections to Magog Court, Copley Hill, and Granta Park have already been considered.

Works during February 2019

  • Install 1100m multi-tube duct through Babraham Institute’s site network.
  • Complete hand-dig sections across high pressure gas pipelines (in liaison with Cadent/NG Gas plant protection engineers).
  • Finalise the design of the GBN into the Genome Campus, in liaison with Jisc and the Campus teams.
  • Plan and schedule the directional drills beneath the A1301 and interconnect site duct.
  • Blow the 14km of 288-core fibre through the completed tube sections.
  • Plan and schedule the necessary additional cabling into Forvie and Addenbrooke’s Level 5 to provide connection through towards the data centre.
  • Continue to capture the 'as-built' duct route, using state-of-the-art GNSS route surveying equipment, to plot the network to ~10cm accuracy using GPS.


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