Micro Trenching for OFC – Method, Uses and Utility Risks

Updated: 23 October 2026

What is micro trenching?

Micro trenching is a fibre installation method in which a narrow slot is cut into a paved road or footpath with a diamond saw or a dedicated trenching wheel, micro-ducts are laid at the bottom, and the slot is backfilled and sealed. Instead of an open trench wide enough for a worker, the cut is only a few centimetres across, and most of the road stays open to traffic as the work moves along.

Operators turn to micro trenching OFC methods mainly in towns and cities, where open trenching means long lane closures, heavy restoration and friction with road owners. It has become a useful tool for city fibre laying: last-mile and FTTH builds, links between cabinets and towers, and short runs across campuses. It does not replace HDD at a major road, rail or canal crossing, and it does not suit every street, as the sections below explain.

How does micro trenching OFC installation work?

Cutting the slot

A saw or rock wheel on a compact machine cuts a continuous slot along the marked line. Duct makers' guidance describes cuts from about 12 mm to 75 mm wide and up to roughly 600 mm deep, with the actual size set by the number of micro-ducts and the road owner's permission. A vacuum unit follows to lift spoil and dust from the slot.

Placing the micro-ducts

Single micro-ducts or bundles are pushed to the bottom of the slot. Corners are cut as gradual curves so each duct keeps its minimum bend radius. Where the slot meets a handhole or chamber, the ducts are led in and sealed.

Backfill and reinstatement

The slot is backfilled in layers, often with sand or a flowable fill, then sealed at the surface with a bituminous, cement-based or resin material matched to the road. Reinstatement matters as much as the cut: a poorly sealed slot lets water in and breaks up the pavement edge.

Blowing the cable

Slim micro cable is blown into the micro-ducts once a section is finished, much as standard cable is blown into larger duct.

Where does micro trenching suit, and where does it not?

The road owner has the final word. Some agencies accept micro trenching on particular road classes with conditions on depth and reinstatement; others prefer conventional methods. Whatever the right of way permission states about cut size and finishing becomes the standard the work is inspected against.

Which micro trenching terms should planners know?

• Micro duct – a small HDPE tube, from about 5 mm to a little over 20 mm across, made to take slim blown micro cable.
• Micro cable – a reduced-diameter fibre cable designed for blowing into micro-ducts.
• Slot or kerf – the narrow cut the saw leaves in the pavement.
• Reinstatement – the backfill and surface seal that restore the road over the duct.
• Bend radius – the tightest curve a micro-duct can follow; corners are cut gradually to respect it.
• Cover – the depth of material above the duct, which decides its exposure to later road milling.

What are the utility risks of micro trenching?

A shallow cut sounds safe because it stays above most deep services, and that is precisely the trap. The upper layers of an Indian city road hold their own crowd of shallow services, laid over decades by different agencies:

• Street-light and signal cables, often just below the surface along kerbs and medians.
• Traffic detector loops cut into the carriageway at signalised junctions.
• LT service cables and house connections crossing the road to properties.
• Water service pipes and small plastic lines feeding buildings.
• Earlier micro-ducts and shallow telecom ducts belonging to other operators.

A saw blade travelling through these lines cuts power, water or data at once, and a live cable strike also endangers the operator. The longer-term risk is the road itself: when it is later milled or resurfaced, a micro-duct with too little cover can be shredded, so the owner's resurfacing plans belong in the design.

Why should the cut line get a GPR scan before micro trenching?

Scanning the planned slot before cutting is the practical answer to those shallow risks. Ground penetrating radar with a higher antenna frequency resolves small, shallow targets well, and that is exactly the zone a micro trench occupies. EM locating confirms live cables, and the crew paints each find on the road so the saw operator can steer around it or stop.

A survey also tests whether micro trenching is the right method at all. If a street proves full of shallow services, a trench in the verge, a different street or a short bore may be safer. Our pre-excavation utility scanning covers short cut lines and work zones, while longer alignments are surveyed under the OFC route GPR survey. Where a major crossing interrupts the route, see how an HDD machine handles it instead.

How should micro trenching be planned and recorded?

1. Check road class and plans. Confirm with the road owner that micro trenching is allowed and no milling or widening is due.
2. Scan the cut line. Survey and mark shallow services before the saw arrives.
3. Fix depth, width and reinstatement. Agree them in the permission, matched to the duct bundle.
4. Plan handholes and turns. Place access points at junctions and branches, with gentle curves at corners.
5. Cut, place and seal in short sections. Keep the open slot short so traffic and rain cannot damage it.
6. Record the as-built. Note the slot line, cover depth and micro-duct count, tied to coordinates, and share it with the road owner.

Shallow micro-ducts are easy for the next agency to cut, so a shared record is the main protection such a route will ever have. The utility mapping page for telecom operators explains how survey data feeds operator records. To have a micro trench line scanned, send the street list or KML through the quote form below.