Direct Buried Cable

Direct Buried Cable: Fibre That Goes Straight Into the Ground

Direct buried fibre cable is designed to be placed in a trench and backfilled, with no duct or conduit around it. It removes the cost of ducting and the labour of duct pulling, but only if the cable's mechanical and moisture protection are specified correctly for the soil and the traffic load above it.

What Makes a Cable Suitable for Direct Burial

• Armouring — a corrugated steel tape or steel wire layer resists crush pressure from soil and stone, and blocks rodent attack. GYTA53 (double sheath, steel tape) and GYTS are the common constructions.
• Radial water blocking — a flooding compound or water-swellable tape behind the armour stops water migrating along the cable if the jacket is nicked.
• Longitudinal water blocking — water-blocking yarn or gel inside the loose tubes prevents water travelling through the tube and reaching splice points tens of metres away.
• Thick outer sheath — a minimum 1.8-2.0 mm PE jacket resists abrasion during pulling and backfill.
• Rodent protection — glass yarn armour or a nylon outer jacket where gophers or termites are a known problem.

Burial Depth and Bedding

• Normal soil, no traffic — 0.8 m cover
• Under roads and driveways — 1.2 m cover, or a duct or concrete slab for additional protection
• Farmland under cultivation — 1.0-1.2 m, below the ploughing depth
• Rocky ground — sand or screened soil bedding at least 100 mm around the cable, plus a protective tile or tape

A warning tape laid 300 mm above the cable is inexpensive insurance against future excavation damage and is mandatory in many jurisdictions.

Installation Practice

• Pull through a straight trench where possible; minimise direction changes
• Never exceed the cable's short-term tensile rating — for a typical GYTA53 this is around 2700 N
• Respect the minimum bend radius: 20x cable diameter during installation, 10x after
• Leave a 5-10 m service loop at each jointing chamber
• Place jointing chambers at accessible locations, not in the middle of a carriageway

When Direct Burial Beats Duct

Direct burial wins where the route is long, straight and stable: rural backhaul, campus links, wind farm collector networks, pipeline monitoring routes and border or perimeter links. Duct wins where future expansion, frequent access or high traffic loading is expected, and in urban areas where the route will be shared with other utilities.

Available Constructions

• GYTA53 — loose tube, steel tape armour, double PE sheath. The default direct burial cable for general soil.
• GYTS — loose tube, corrugated steel tape, single sheath. Lighter and cheaper for protected trenches.
• GYTA33 — steel wire armour for river crossings and exceptionally high crush risk.
• GYFTY53 — non-metallic, for routes that must remain dielectric.

Testing After Backfill

The trench has barely been closed before the cable is out of sight for the next twenty-five years, so testing must be thorough. Run an OTDR trace on every fibre before backfill — while a fault can still be repaired by hand — and again after backfill to confirm nothing moved. Record both traces as the acceptance baseline. Measure end-to-end insertion loss against the calculated budget, and verify continuity on every core against the labelling record. Any fibre that fails should be repaired immediately; retro-excavation costs many times more than a splice made at the time.

Documentation to Keep

• As-built route drawing with the cable position offset from a permanent landmark
• Joint and chamber GPS coordinates and their unique identifiers
• OTDR trace files, before and after backfill
• Fibre allocation table showing which core serves which customer or circuit
• Cable drum and batch numbers for each section, for future warranty claims

Ordering

Huifiber supplies direct buried cable from 2 to 288 cores with steel tape, steel wire or dielectric armouring. Tell us the soil type, burial depth, expected traffic load and whether the route must be non-metallic, and we will specify the right construction and armouring grade.