What Is an Intersect Bore? The Hardest Trick in HDD

Picture two drill rigs on opposite banks of a river, each boring a hole underground, aimed at each other, trying to meet in the middle. Hundreds of feet down, thousands of feet apart, in the dark, through whatever the ground decides to throw at them.

That’s an intersect bore. And when it works, it’s the closest thing our industry has to a magic trick.

What an Intersect Bore Actually Is

Most horizontal directional drilling is done with one rig. It drills a pilot hole from entry to exit, reams it bigger, and pulls the pipe back through. One machine, one path, start to finish. (If that part’s new to you, start with What Is Horizontal Directional Drilling.)

An intersect bore uses two rigs instead of one. Each drills a pilot hole from its own side, and the two bores are steered to meet at a precise point underground, the intersect. Once they connect, the crews effectively have one continuous hole spanning the entire crossing, drilled from both ends at once.

Then it’s back to the usual program: ream the hole to size, pull the pipe through. The hard part is the meeting.

Why Anyone Would Do It This Way

Drilling from both ends sounds like twice the work, because it is. So why bother?

• Length. On the longest crossings, a single rig physically can’t push or pull a drill string the whole distance. Splitting it in half from two directions makes the impossible possible.
• Difficult ground or deep crossings. Under wide rivers, sounds, and bays, an intersect keeps each bore shorter, more controllable, and less likely to wander off course over a long run.
• Accuracy. Two shorter, well-steered bores can hold a tighter path than one giant one, which matters a lot when you’re threading a specific depth under a waterway.
• Risk. If something goes wrong, you’ve got two access points and two crews instead of one long shot you can’t reach the middle of.

In short: intersect bores are how you get the biggest, longest, most demanding crossings done when a standard bore simply runs out of road.

The Part That Makes It Hard

Here’s the catch. Those two bores have to actually meet, within inches, somewhere deep underground where nobody can see anything.

That’s done with specialized magnetic guidance systems that let each crew know exactly where the other drill head is, and steer toward it in real time. It takes precise surveying, constant communication between the two sides, and crews who’ve done it enough to trust the numbers when their gut is telling them they’re about to miss.

When the two bores connect, you can feel it on the rigs. When they don’t, you’re re-drilling. There’s not much room in between.

This is why intersect bores separate the contractors who say they do complex work from the ones who actually can. It’s not equipment you can just rent your way into. It’s reps.

We’ve Done the Hard Ones

This isn’t theory for us. NCDD has completed intersect crossings that the industry’s leading publication, Trenchless Technology, thought were worth writing about, including an intersect bore under the Roanoke Sound and a coordinated 10,000-foot intersect crossing. You can see that coverage on our media page.

Those are the jobs that don’t go to the lowest bidder with a big rig. They go to the crews who’ve stood on both banks before, watched two bores find each other in the dark, and know exactly what it takes to make it happen again.

So, Do You Need One?

If your crossing is long enough, deep enough, or under enough water that a standard single-rig bore is getting nervous, an intersect might be the answer, or it might be overkill. That’s a judgment call, and it’s one worth making with a contractor who’s actually executed them, not one reading about it for the first time on your project.

We’ve built our large diameter and complex crossing work around exactly these situations. If you’ve got a crossing that other people keep calling “impossible,” that’s usually our cue to get interested.

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Got a crossing that might need an intersect bore? Tell us about it. We’ll give you a straight read on whether it does, and what it’ll take to pull it off.