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How does a horizontal directional drill work?

Horizontal directional drills (HDD) are used for trenchless pipe, cable and duct underground installations (you can browse our range here).

Here we look into how a HDD actually works and what the top applications of these types of drills are within the underground sectors


What is a horizontal directional drill?


A horizontal directional drill is a type of drill used in the underground sector. The drills come with different attachments, including rods and fluid reamers, and are used as a guided, trenchless method of installing underground pipes, cables and duct.

The trenchless nature of their use means that horizontal directional drills use only a very small footprint compared to other traditional installation methods. Operations using HDDs also tend to be more cost-effective too.

The process is known as ‘horizontal’ directional drilling, as the pipes are installed horizontally under the ground and often involve directional changes.


How does a horizontal directional drill work?


The process involved in horizontal directional drilling can be summarised in three main steps:

1. Digging a pilot hole

To begin with, a borehole is drilled along a predetermined path in the ground by the horizontal directional drill. The drilling head is hollow and is pushed through the ground, steered by the driller who uses a transmitter to determine the precise location of the drilling head.

2. Pre-reaming

The pre-reaming stage involves using the horizontal directional drill to enlarge the pilot borehole. It is completed in stages and ensures that pullback pressure will be lower when the pipe is eventually installed. Completing it in stages also means that the structural integrity of the hole is maintained.

Drilling fluid is also pumped in to remove solids and enlarge the hole. The fluid also helps maintain the structural integrity of the hole.  

3. Pipe pullback

The final stage of pipe installation using a horizontal directional drill is pipe pullback. This is where the drill string is pulled back along the path of entry and the pipe is inserted in its place. Pipe pullback involves calculating the force required when pulling the drill string back as an incorrect force could damage the structure of the hole or product being installed.


What are the top applications of a horizontal directional drill?


Horizontal directional drills are used for a variety of applications where trenchless installation is preferred or required. The environments themselves include residential areas, urban areas, under roads, rivers or environments with unstable soil conditions. This is because of the lesser footprint offered by horizontal directional drills in comparison to trenching methods, which means minimised disruption to the site’s surroundings.

Horizontal directional drills are frequently used for all types of utility installation in urban and residential areas and all utility pipelines under obstructions.


Horizontal directional drills have a wide range of benefits for drillers that can be summarised by their efficient nature of installing pipes and cables, with less disruption than methods that involve trenches.

The process involved in horizontal drilling also requires calculating the precise tensile force needed to maintain the structural integrity of the hole before installing a pipe, and transmitters are used to determine the location of the drill head for precision.

To find out more about the range of horizontal directional drills offered by Vermeer, you can contact our team of experts on 01933 274400 or email us at Alternatively, fill out an enquiry form with details of your request and we’ll get back to you.

Vermeer Corporation delivers a real impact on the way important work gets done through the design, manufacture and support of high-quality industrial and agricultural equipment that helps connect people to the necessities of life, manage natural resources and feed and fuel communities. With a reputation for being built tough and built a better way, that equipment is backed by localized customer service and support provided by independent dealers around the world. To learn about Vermeer Corporation, products, the dealer network, financing options and careers, visit


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