The Basics of Trenchless Microtunneling Projects

By Denise Sullivan
Published: September 25, 2020 | Last updated: July 5, 2023
Key Takeaways

Microtunneling is an option for small diameter pipelines. This trenchless construction technique is excellent for pipes spanning long distances and have a rigid construction.

Boring into the ground to lay new pipe is a time-consuming project. There are many ways to run a new line in a place where no previous line existed. Traditional open trenches are hazardous to workers and the environment. Trenchless technology, such as microtunneling, is a viable solution to consider.


What is Microtunneling

As the name implies, microtunneling is a technique that uses the construction of small tunnels to lay pipe. These lines are tiny in comparison to traditionally used piping, running from 0.61 to 1.5 meters. Plumbing as little as 150 to 3000-millimeters in diameter is possible.

All microtunneling has four key attributes. It consists of a boring machine controlled by remote. The machinery uses a guidance system. Operators use pipe jacking to install the new pipeline. Finally, there is continuous pressure exerted at the excavation point to balance earth and groundwater pressure. (Read also: Balancing Soil Pressure During Microtunneling.)


An operator controls the microtunneling boring machine, or MTBM, remotely. Due to the small size of the bore and the installation process, personnel cannot enter the area. This means the control panel and operator remain on the surface during the procedure. This trenchless machine uses either vacuum soil removal, slurry or augers to install the new lines.

Microtunneling VS Traditional Trenchless Tunneling

While there are a variety of trenchless tunneling techniques, microtunneling stands apart from the rest. For starters, microtunneling is far more accurate than other traditional trenchless tunneling methods. Unlike other tunneling efforts, this version uses a guided system to ensure accurate installation of the pipes. This is due to the small diameter bore making it impossible for personnel to enter the excavation. (Read also: An Overview of Trenchless Tunneling.)

In addition to its high-end guidance system, microtunneling is a pit-launched tunneling technique. This means that workers dig a small pit next to the area the lines run for the machine to sit.

Other tunneling techniques, such as horizontal directional drilling (HDD), do not need a launch pit to work. Instead, HDD machines work from the surface and drill pipes into place. While this makes them quicker, HDD is not as accurate, and the pipes used need to be flexible as they must bend before reaching their gradient.

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When to Use Microtunneling

Microtunneling is a more expensive trenchless construction technique. Because of the cost and time it takes to dig the launch pit, this option is often left for projects that require a great deal of accuracy over a long distance.

There have been developments in technology that allows for significant bore pipelines to have curved drives. However, the traditional design and usage of microtunneling indicate the technique’s best use is on a smaller diameter, rigid construction pipelines, such as those used for sewage and gas lines.

When Not to Use Microtunneling

It is true that microtunneling technology has advanced to the point the technique is useful on larger diameter pipelines. However, use large bore lines are not the original use. Other, more efficient, technologies are available for pipes wider than 1.5 meters in diameter. (Read also: Planning a Microtunneling Project: What You Need to Know Before You Begin.)

It's worth noting that pipes that need a curved drive, or are flexible, do not work well with microtunneling. For these bores, using HDD or pipe jacking techniques might be a better solution.

For help with determining the best method for your project, be sure to visit our Trenchless Construction Methods Calculator for customized recommendations tailored to the needs of your upcoming project.

Final Thoughts

Trenchless construction projects come in all shapes and sizes. While traditional tunneling techniques are useful for many projects, especially those in need of curved drives, microtunneling is a viable option for small diameter pipelines. The accuracy driven by these machines allows operators to ensure the new lines are in place without risk to personnel. While Microtunneling may be a more expensive route, the minimal environmental impact can make a difference when laying new water, sewage and gas lines.

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Written by Denise Sullivan | Technical Writer @ Trenchlesspedia

Denise Sullivan

Denise Sullivan is an accomplished freelance writer from Louisiana, with a Associate's Degree in Journalism from Eastern Oklahoma State College. She also graduated from East Central University with a Bachelor's in Biology. Denise began her writing career writing operations and maintenance manuals and software utility manuals for flight simulators. Since, she has expanded her writing to a broad spectrum of topics.

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