Installing fibre-optic cables underground

By Neil Bradley, Fibre Options

Analysis shows that between 60% and 80% of the capital costs of a fibre project are due to civil work, ducts and cables. In other words, the cost of digging holes and filling them in again.

There are ways of getting round these costs, such as wireless transmission, overhead poles, and so on, but in the main if a future-proof network is to be employed then only fibre will do the right job.

Costs for digging can vary enormously, from £5 per metre to £100 per metre depending on where you are going and what disruption you are incurring. If permissions have to be granted they can depend on the traffic control of diversion of that area, which is costly. If the digging is in soft areas and reinstatement is not a problem then costs are low. If the dig can be achieved by slot cut with a very narrow channel then costs are about £25/metre. Costs then escalate up to £35 to £50 per metre for cutting into the pavement and could be £100 per metre in the main carriageway.

Over the past few years, lower cost alternatives to traditional trenching have emerged.  Here we will introduce some of these methods.

Micro-Trenching

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Micro-trenching is particularly suited to roadways and sidewalks where utilities are already present beneath the road surface.  It requires only a shallow trench, typically about 15 cms deep, which does not penetrate beyond the surface layer of the road.

Advantages: Significantly faster and less expensive to deploy than traditional trenching - approx. 35% less. There is less damaging to existing roadways.  Less depth also means that cables are closer to the surface, easier to get to and fix if there is a problem.

Moleploughing

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This installation method is suitable for burying cable or sub-duct in rural verges or across farmland. Specialist machines ‘plough’ a slot directly into the ground and lay the cable or sub-duct into the slot immediately, in one continuous operation.  The ground then closes over the slot and needs no re-instatement.  

Advantages: Significantly faster and less expensive to deploy than traditional trenching - typically 40% cheaper.
Disadvantages: Moleplough products are generally somewhat tougher than standard designs in order to match the heavy duty installation method.

Directional Drilling

Directional drills are relatively compact, allowing them to get into tight spaces and to be placed at the side of a road without impeding traffic.  A small crew is required: a drill operator and locating equipment operator.  The locator operator electronically tracks the progress of the drill head beneath the surface using a hand-held locator.  He also gathers data from the sonde located in the drill head behind the drill bit.
The sonde gathers data such as location, depth, roll angle, pitch, and temperature to help the driller adjust the direction of the head and control the bore path.

Advantages: Clean, trenchless solution without disturbing the surface above, leading to cost savings in excavations, reinstatement costs.  No more need to apply for road-opening permits for public road works.

Impact Moling

Unlike horizontal directional drilling – which can be guided – impact moling works in straight lines, and requires both a launch pit and a reception/catch pit. In the launch pit, the mole is lined up with the catch pit and then set in motion. Impact moling has many applications including the renewal of lead water pipes, the installation of utility pipework and cable-laying.

Advantages: Suitable for all soil conditions except rock. Minimal or no excavation beyond the necessary connection pits, and minimal disruption to the customer and customer’s property.

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