HDD vs Microtunneling | Pros and Cons of Each Method

Today we are going to compare two common trenchless methods; horizontal directional drilling (HDD) vs microtunneling. Both are used for utility installation, such as pipelines, in urban areas and environmentally sensitive areas. This is because their trenchless technology allows for minimal to no disruption to the ground surface.

However, each method has its pros and cons, which we are going to explore in this blog. Find out which trenchless installation technique best suits your upcoming project.

Launch and retrieval

In horizontal directional drilling, the process begins at the launch point, where a drilling rig is positioned to drill a pilot hole along a predetermined path beneath the ground. Once the pilot hole reaches the retrieval point on the other side, the hole is enlarged using a reamer, which is pulled back to the launch point. The remaining process may be performed in several stages, depending on the required diameter of the hole. Once the hole is appropriately sized, the product pipe is attached to the drill string at the launch point and pulled back through the hole to the retrieval point.

In contrast, microtunneling launch and retrieval involve more specialised machinery. At the launch shaft, a microtunnel boring machine (MTBM) is introduced into the ground and remotely controlled by an operator at the surface. The MTBM excavates the tunnel and simultaneously pushes the pipeline sections into place behind it. The excavated soil is transported back to the launch shaft via a slurry transport system. Once the MTBM reaches the retrieval shaft at the end of its run, it is removed from the ground, often with a crane’s assistance.

Size and accuracy

HDD is typically used for smaller to mid-sized projects, with the capability to install pipes with diameters ranging from 2 inches to 48 inches, and over lengths from 600 feet to 1800 feet. Microtunneling, on the other hand, is generally used for installing pipelines of larger diameters, typically ranging from 12 inches to 48 inches. In terms of length, microtunneling can install pipelines over several thousand feet, with some projects exceeding a mile.

When it comes to accuracy, HDD depends mostly on the skill of the operator and the quality of the guidance system, with modern systems providing real-time feedback to ensure the drill head follows the planned path. Microtunneling, however, uses a laser guidance system and a hydraulic jacking system that maintains continuous support of the excavation face. This allows the operator to make fine adjustments and ensures the pipe is installed precisely as planned.

Soil compatibility

HDD is a versatile drilling method that can handle a wide variety of soil conditions, particularly soils made up of hard, medium, and soft rock, but also loam dirt and clay. However, certain soils can be problematic for HDD. For instance, loose or poorly consolidated soils, such as sand and gravel, can cause instability in the borehole. Similarly, in the case of hard rock, more specialised equipment and additional time might be needed to complete the project.

On the other hand, microtunneling is exceptionally well-suited for unstable soil conditions, including sandy, silty, or clayey soils. The process employs a slurry system, which maintains face pressure during excavation, thereby stabilising the tunnel face and preventing the borehole from collapsing. However, in mixed ground conditions or where boulders are present, microtunneling can face challenges.

Impact on the surroundings

HDD has a small footprint as it only requires entry and exit pits, reducing disruption to surface activities significantly. This makes it suitable for environmentally sensitive areas and urban settings. It also minimises soil displacement because the borehole diameter is typically only slightly larger than the pipe being installed.

Like HDD, microtunneling requires minimal surface space, limiting disruption to surface activities. However, it typically displaces a larger volume of soil compared to HDD because it usually involves installing a larger casing before the utility pipe. This leads to more waste generation that must be managed responsibly.

Overall costs

HDD generally requires fewer crew members than microtunneling, which can lead to lower labour costs. Additionally, equipment for HDD tends to be less complex and thus less expensive than for microtunneling. However, costs can vary depending on the complexity of the drill path and the type of ground conditions encountered. Maintenance costs are also generally lower compared to microtunneling and the cost-effectiveness of HDD is often seen in projects with long, straight bores in consistent ground conditions. The speed at which HDD can operate in these situations often results in lower costs in terms of time and labour.

Microtunneling equipment is generally more expensive due to its complexity and the advanced systems required for precise control. Additionally, it typically requires a larger crew to operate, contributing to higher labour costs. Maintenance is also more costly compared to HDD due to the complexity of the equipment and the abrasive nature of the cutting process. 

Which trenchless method is right for you?

Horizontal directional drilling:

• Ideal for small to mid-sized projects that require pipeline installation with diameters ranging from 2 inches to 48 inches, and over lengths from 600 feet to 1800 feet.
• Great for installing pressure pipelines such as gas, water mains, pump sewers, and cable pipes.
• Best suited for soils made up of hard, medium, and soft rock, but also loam dirt and clay.
• Smaller soil displacement because the borehole diameter is typically only slightly larger than the pipe being installed.
• Generally more cost-effective because it requires less labour and maintenance is cheaper.

Microtunneling:

• Ideal for installing pipelines of smaller diameters, typically ranging from 12 inches to 48 inches, over a distance of several thousand feet.
• Great for installations that require high accuracy and precision such as gravity sewers.
• Better suited for unstable soil conditions, including sandy, silty, or clayey soils.

Vermeer’s HDD solutions

At Vermeer WA & NT, we supply a wide range of horizontal drills ideal for trenchless construction and long crossings. For utility installation in highly urbanised areas, we recommend the compact D23x30 S3 and D24x40 S3. These models offer quiet HDD drilling, so the surrounding homes and offices are not disturbed.

For jobs that require larger-diameter pipeline installation over longer distances, we recommend our powerful D40x55DR S3 and D60x90S. These machines can easily drill through rock and offer great productivity rates. 

Today we only mentioned four of our HDD models, so be sure to check out our whole range of Vermeer directional drills to find the right one for your job. Contact us for more information or for a free quote. One of our friendly team members will be happy to assist you.