HDD Basics: Can your construction firm get in on this booming industry?

HDD was invented as an alternative to digging an open trench because it allows for miles of underground work to be done with minimal disruption to the surface and surrounding areas

Right now, across the United States, the horizontal directional drilling (HDD) industry is booming.

Among the growing need to expand the world’s high-speed fiber networks; upgrading existing infrastructure like electric, gas, water and sewer; and the need to relocate aboveground utilities underground, the demand for HDD is likely to continue growing.

HDDs and crews have become a common sight on the streets of communities across the nation. If you haven’t worked around these machines or been part of a utility construction crew, you may wonder why HDD is the preferred method for certain underground installations — and how HDD works.

What exactly is HDD, and why use it in place of open-cut methods?

HDD involves creating a tunnel, or bore, underground to install utilities with pipe, conduit or cables that place fiber, electrical, gas and water lines. This method was invented as an alternative to digging an open trench because it allows for miles of underground work to be done with minimal disruption to the surface and surrounding areas.

Experts explain that, although there are basic economics involved when deciding whether to use HDD or open-cut methods, such as equipment, labor and restoration costs, there are often additional factors contractors should consider. These factors include ground conditions, diameter of the product, grade requirements, underground and aboveground obstacles, and location.

Urban and rural locations present different challenges and opportunities

In countries like the U.S., which have more developed infrastructure, HDD is usually the preferred installation method for small-diameter utilities in urban and suburban locations. Minimizing restoration, avoiding traffic disruptions and keeping property owners happy are a few of the reasons why it is so often used in populated areas. Boring a utility line is generally more cost effective and takes less time because the bore goes under roads and sidewalks, not to mention other aboveground obstacles like fences and driveways.

In rural areas, since there is often less restoration and fewer obstacles to contend with, trenching and/or plowing is typically faster and more cost effective

Before any work can begin on the site, utility companies must be called in to locate their underground services

for a smaller-diameter product. However, the contractor still needs to account for existing utilities, type of soil, size of the product and required depth. For deeper installations or in rocky soil conditions, HDD may still be the best choice because less material must be removed during the installation process. And of course, trenchless technology should still be used for passing under roadways, rivers and other aboveground obstacles.

What equipment is used for directional drilling?

The success of the HDD method is based on certain key pieces of equipment. Understanding capabilities and limitations of the equipment is vital to a successful project. Brief general descriptions of the required equipment follow.

Drilling rig - The two main functions of a drill rig are rotational torque (turning force) and thrust (pushing-and-pulling force). Together, these two functions work to turn and push the drill head and drill bit through the ground to create an initial hole, or pilot bore.

As the drill is working, more drill rod is added so it can continue to create the bore. Once this pilot bore is made and the drill head is exposed above ground at the end of the bore, the product being installed is hooked up to the drill string and pulled back underground. Each drill can be equipped with different tooling based on ground conditions. There are various sizes of drills, depending on the size of the product being installed, ground conditions and distance of the bore.

Tooling - “Tooling” typically refers to the actual drill bit/drill head, transmitter housing and drill rod. The drill bit is a piece of solid, heavy metal that is angled appropriately to cut the ground and direct the installation. This drill head and bit move through the ground with twisting and pushing motions, cutting away at the soil to create the hole, or bore. Steering and pushing the drill head allows it to change direction and depth.

To accommodate drilling in harsh conditions, rock tooling — including air hammers, polycrystalline diamond compact (PDC) bits and economic rock tooling packages — are available along with a wide range of reamers, swivels, adapters and pulling eyes.

Drilling fluid - Drilling fluid is used to carry the soil cuttings out of the bore as the drill is working. Drilling fluid is mostly made up of water, but various drilling fluid products are generally added. The result is drilling fluid, usually referred to as “mud” by the crew. Adding different products gives the water certain desired properties such as gel strength and lubricity. Importantly, it also forms a thin layer of material to help strengthen the hole and keep the mud inside.

Drilling fluid is mostly made up of water, but various drilling fluid products can be added to give the water certain desired properties such as gel strength and lubricity

Vacuum excavator - Another important piece of equipment used on an HDD jobsite is a vacuum excavator or hydro excavator. This machine uses high pressure water with a special nozzle to cut the ground while simultaneously using a high-flow vacuum to suction the loose ground up. A vacuum excavator can create a hole in the ground, uncovering existing utilities, while reducing the chances of a utility strike.

Vacuum excavation is used prior to the drilling process to expose any existing utilities along the intended installation path. Vacuum excavators are also used to remove spoils (used drilling fluid) from the site to be disposed of at an approved dump site.

Mixing system - A mixing system mixes the drilling fluid products mentioned above and supplies it to the drill so the drill can get through the ground efficiently. It also keeps the mixture agitated throughout the drilling process.

Locating system - A locator is used to help guide the drill head underground by following its path. It is critical that the drill head stays on the pre-determined path so it avoids utilities and other potential obstacles underground.

Once the drill and its transmitter are underground, the locator recognizes and communicates with the transmitter signal and displays a position, pitch or angle, temperature of the transmitter, downhole pressure, and drill head depth. This information is used to help steer the drill head along the correct path.

What is the HDD process?

Before any work can begin on the site, the utility companies must be called in to locate their underground services. Those locates may be done by the utility companies, municipalities or a third-party contractor. After those are completed, best practices require contractors to verify the locations of the utilities themselves.

Many contractors will use their own utility locators to confirm that the flags and paint on the ground are correct. However, to ensure they do everything possible to avoid striking an existing utility or, worse yet, a cross bore, the exact location and depth need to be confirmed by actually exposing those utilities. Some contractors use mini excavators or shovels, but those methods risk inadvertently striking and damaging the lines they are trying to uncover.

A better way to expose the utilities is to use a vacuum excavator to soft-dig, or “pothole,” an area above the underground utility. Vacuum excavators use water or air to break up surface material while a suction hose immediately removes the spoils. Once the utility locations have been confirmed, the drill is moved on site.

On a typical job site, there will be an operator running the HDD and a person using an above-ground receiver, called a locating system, tuned to recognize the transmitter, or sonde, in the transmitter housing connected to the drill string and drill bit.

The locating system shows the position, pitch or angle of the drill head, and depth of the drill head. The locator is held by a member of the crew who is walking the installation path. That person uses a radio to communicate with the operator of the drill, informing them of the position of the drill head.

The HDD itself is a machine that holds multiple rods (or pipes) that connect to each other and push through the ground to make a bore. From aboveground, the rods enter underground by poking into the soil or through a small dug-out pit. The drill head and bit move through the ground with twisting and pushing motions, cutting away at the soil to create a hole, or bore.

Once the tooling reaches the desired end location — in the case of installing conduit for fiberoptics, for example— a piece of tooling (usually a swivel) connects the conduit to the drill string and is pulled back to the entry side of the bore. Later, crews come back to blow fiber through the conduit and splice the lines together. This basic process applies to all kinds of pipe, conduit and other underground product.

To aid the bore, drilling fluid is used to carry the soil cuttings away. Besides the advantages mentioned earlier, the drilling fluid also helps provide coolant for the downhole transmitter (sonde) in the transmitter housing and reduces wear on tooling.

Why is horizontal directional drilling used?

Since its introduction, HDD has benefited communities and neighborhoods. For comfortable modern life, underground utilities are a necessity. And with HDD replacing open-cut methods, lawns and parks and other public places can retain their pristine condition.

Significantly fewer linear feet of paved roads and streets need to be torn up by utility workers, making upgrades to infrastructure much less intrusive. As fewer feet of roadways are disturbed, even traffic can flow almost normally, even during an install.

HDD is a growing industry with a high demand for skilled trade workers. Much like other sectors of the construction industry, HDD contractors are actively searching for the right people to train to become part of their teams.

Today the HDD industry is growing steadily with the high demand for fiber work, and for larger-diameter work as well. It’s no secret the Covid-19 pandemic has put a strain on global broadband capabilities, which is leading many governments, including those in North America, to launch infrastructure improvement initiatives that include all types of underground utilities.

HDD will be in high demand for many years to come.

Dan Vroom is industrial training manager at Vermeer Corporation.