Horizontal directional drilling (HDD) has been around since the 1960s, and today is one of the most common ways of installing underground pipes and utilities.
Workers gravitate toward the drilling process because it doesn’t damage the landscape nearly as much and is less obtrusive than open trench digging. For companies, horizontal directional drilling offers several benefits, as it’s faster and safer than traditional installation methods, needs less equipment, and doesn’t require as many workers on the jobsite, making it a low-cost installation option.
You’ll often find HDD teams working in areas where pipes or conduit needs to be installed, but excavation isn’t the best option. It also works well for situations where tunnels need to be deep underground, under other utilities or in spots where there might already be other utilities installed.
Directional drilling takes place in several steps but starts with a pilot hole drilled at the entry point.
The pilot hole is a small tunnel created by a drill traveling along a pre-determined bore path. Workers guide the drill from above ground, and sensors in the drill head send data back in real time as the tunnel is formed. The information sent back to the workers helps them make sure the drill stays along the centerline of where the proposed utilities will be installed.
Once the pilot tunnel is drilled, a reamer is attached to the drill line and is pulled back through to the initial opening. The reamer helps open the tunnel so that it ends up being slightly larger than the pipe or conduit getting installed. At the same time, a slurry made of drilling fluid is also pumped into the borehole to remove cuttings, help clear the pathway for the reamer, and ensure a smooth boring process.
During the final pass through, the reamer will pack the soil around the edges of the borehole and make sure the path is completely clear for the pipe’s installation. Typically, when all is said and done, the borehole will be somewhere between 1.25 and 1.5 times larger than the installed pipe. This extra room offers enough space to install the pipe or conduit without damaging it, though it does mean there will be some settling later.
After the tunnel is drilled, aircraft cable is connected to the pipes or conduit that needs to be installed and is carefully pulled through the borehole. Any other wires, cables, or other assets are pulled through the piping or conduit and the project is finalized.
It’s important to always use the right tool for the job, and the same can be said for installing utilities.
There are several times where the HDD approach makes sense, including:
There are two wires commonly used in directional drilling:
Directional Drilling (HDD) Tracer Wire: This wire is like a traditional tracer wire but is made of a more durable insulation that can withstand the harsher environments associated with the drilling process. This guarantees your tracer will still be in one piece when you need to use it.
Horizontal Directional Drilling Wire (HDD): Often called the ‘wireline,’ HDD wire is used for directional drilling when a wireline monitoring system is needed, rather than an above-ground, or ‘walk-over,’ monitoring system.
This wire runs inside the drill string and transmits information about the angle, rotation, direction and temperature of the drilling head while it’s working underground, out of sight. It’s manufactured to withstand the harshness of the drilling process and delivers reliable electrical signals to the guidance control.
When done correctly, horizontal directional drilling can save your crew time, effort, and money over the course of an installation project.
Workers are safer because they don’t have to worry about falling into open trenches and cave-ins and can move more quickly because there isn’t a lot of landscape care or pavement fixing that needs to happen. Utility companies enjoy the smaller crews needed to complete the job, and not having to bring in as much heavy machinery in to get the job done.
Combined with a solid tracer wire system, it’s possible to install and maintain underground utilities safely without causing damage, issues, or delays.