Horizontal Directional Drilling (Boring)

Horizontal directional drilling (HDD) installs fiber, gas and water lines underground without open trenches. Because you can’t see where the drill head goes, striking existing utilities is the biggest risk.

• Construction
• Utilities
• Telecom

Hazards

• Utility strikes: gas lines (fire and explosion), power cables (electrocution), water and fiber
• Cross-bores: a new gas line bored right through a sewer lateral. Later, a plumber clearing the sewer can cut the gas line, causing an explosion, sometimes years later.
• Rotating drill rods and wrenches that can catch clothing and limbs
• High-pressure drilling fluid lines
• Traffic around street work

How a bore works

1. Pilot bore: a steerable drill head bores along a planned path while a locator on the surface tracks its depth and direction.
2. Reaming: the hole is enlarged by pulling a reamer back through it.
3. Pullback: the new pipe or conduit is pulled into the hole.

Drilling fluid (usually water and bentonite clay) cools the tool, carries cuttings out and holds the hole open. It’s pumped at high pressure.

Planning the bore

• 811 ticket and locate marks confirmed; private lines located
• Every utility crossing and parallel line within the tolerance zone potholed to confirm depth
• Bore plan with entry and exit pits, depths and required clearance from other utilities
• Sewer laterals identified and camera-inspected where the bore crosses them
• Strike system set up and tested; mats in place
• Traffic control set up for street work
• Plan for inadvertent returns (drilling fluid surfacing through cracks, into basements, streams or storm drains)

Safe practices

• Call 811, then pothole (expose by hand or vacuum excavation) every crossing utility to confirm its depth. See Hydro & Vacuum Excavation.
• Plan the bore path and track the drill head with a locator.
• Use the rig’s electrical strike system: grounding stake, voltage alarm, and operators standing on equipotential mats.
• Inspect sewer laterals with a camera before and after boring near them to check for cross-bores.
• Keep everyone away from rotating rods; stop rotation before handling rods.
• Use the rig’s interlocks and guards. Don’t stand in the rod loader or vise area while the rig can move.
• Check high-pressure fluid hoses and fittings daily, and never use your hand to find a leak.
• Record the bore path (depth and location) as you go, so accurate maps exist for the next crew.

• Don’t bore blind across a marked line without exposing it.
• Don’t rely on map depth or locate marks alone. Marks show approximate horizontal location, not depth.
• Don’t keep drilling if fluid pressure suddenly drops or the rig behaves strangely. Stop and investigate.

Last updated: October 1, 2026