A Quick How-to Guide for Underground HDD Steering and Tools

Horizontal directional drilling necessitates the use of underground steering (HDD). It is quite rare to have a project where no previous underground constructions, some of which may be unrecorded, are already in existence. You can get around these barriers by steering.

The tighter the steering control, the closer you can get to other installations without colliding with them.

The ability to maintain track of the actual underground route is another advantage of steering systems. Because of the known underground impediments at any given place, future trenchless projects in the area will be significantly easier with the help of these systems.

The Basic Principles Of Underground Steering

Access to the following is required to steer an HDD rig:

  • Knowing which way the drill is pointed.
  • The ability to change course.
  • Drilling position underground that has been calculated or externally validated.

A non-rotating drill string is used by an HDD rig when drilling the pilot hole. The leading edge of the drill bit is asymmetrical. The drill string is twisted so that the leading-edge faces in the new direction to alter the direction. The procedure is straightforward, and it allows operators to change the drill’s direction at any point during the process.

The more challenging task lies in determining the drill’s current position and how much the direction needs to change.

In general, a drill’s direction is determined by two variables: azimuth and inclination.

The azimuth specifies the drill’s orientation in relation to the North, whereas the inclination tells whether the drill is pointed up or down and how much.

What are the Different Types of Underground Steering Tools?

HDD steering tools are classified into two types. The magnetic tool that uses magnetic fields, and the gyro tool that uses accelerometers and fiber-optic gyroscopes to calculate drill location. Wires connect the steering tools to equipment on the ground that performs calculations and makes adjustments.

Gyro Steering Tools

These tools have the advantage of not requiring any magnetic field to function. This is useful in situations where there are external magnetic fields that would cause a magnetic steering tool to fail. Magnetic steering tools can be hampered by high-voltage cables, trains, and cathodic protection systems.

Gyro tools have their drawbacks too. The position of the gyro tool under the ground cannot be verified externally. Because they are magnetically insensitive, they are unable to detect other underground structures and may collide with them if the operator is unaware of their location.

Moreover, these steering tools are generally expensive, and their utilization necessitates trained operators. They are, however, faster to deploy because they do not require the installation of magnetic coils on the surface — making them an absolute must in every hdd contractor’s tool kit.

Magnetic Wireline Steering Tools

Magnetic fields are used to determine the position and direction of magnetic wireline steering equipment. The ability to track the drill from the surface using a coil and its magnetic field is a significant advantage. It’s critical that the actual steering tool is housed in a magnetic collar so that its measurements aren’t interfered with by other magnetic fields.

Tracking from the surface may be hampered by infrastructure or environmental elements such as lakes and rivers.

Magnetic steering systems are less expensive and easier to use than gyro systems. However, due to the surface tracking technology, the setup time is greater.


Steering precision is greatly enhanced by tracking a drill from the surface. Because it continuously monitors the drill’s actual position from the surface, the walkover system actually delivers the most accurate steering. However, most applications render this method infeasible due to the existence of infrastructure or bodies of water, making standing over the drill impossible.

A coil on the surface is used to generate a magnetic field in the next best tracking method. The drill’s magnetic sensors provide readings that enable operators to precisely locate the drill. After that, the steering calculations are updated using the current position.

These changes ensure that the steering system always uses the actual position to determine which steering adjustments should be made.

It’s worth noting that there’s no way to check the position of a gyro steering gadget from the outside. This steering approach relies solely on computations because magnetic fields have little effect on the gyro. Any faults that occur throughout the drill cannot be offset, and any errors that exist in the system will be compounded throughout the drill route.

As a result, some trenchless construction practitioners believe that the magnetic steering approach is the most precise tool.

The Future of Steering

Underground steering is critical to HDD success. As a result, gyro and magnetic steering technology are always developing. There is no one-size-fits-all answer for all applications. Engineers and hdd contractors must examine each job’s individual requirements and recommend the appropriate system.