An Overview of Trenchless Tunneling

By Tabitha Mishra
Published: May 26, 2017 | Last updated: July 20, 2023
Key Takeaways

Trenchless technology encompasses various methods of cnstruction like microtunneling, auger boring, moling and horizontal directional drilling.

Signs reading “Road Closed” have almost become a thing of the past, thanks to trenchless technology. There was a time when laying new pipelines or undertaking repair for leaking water or sewer pipes was a nightmare for neighborhood homes, offices, schools and businesses.


Not only did it involve digging up long stretches of roads and sidewalks, but sometimes, the excavation would run right through an immaculately maintained private property. Other than it being inconvenient, and an eyesore, there were other implications like higher cost, more time, safety concerns, storage issues and disruption of traffic that had to be dealt with.

Often repairing pipelines meant disrupting telephone cables, electric lines and other utility pipelines that run underground. Trenchless technology has dealt with all these problems and much more with its use of the latest technological advances that enable faster, cheaper and least disruptive methods to carry out installation and repair of underground pipelines. (Read Trenchless Rehabilitation Evaluation: How to Properly Inspect and Locate Damaged Pipelines.)


What is Trenchless Tunneling?

While the concept of trenchless tunneling is not new, it is a fairly new venture in the field of construction for the purposes of laying water and sewer pipelines. Tunnels that serve as passes for vehicles through mountains and underwater bodies are also constructed using trenchless technology and utilize entry and exit points.

It is one of the oldest forms of trenchless tunneling and employs huge tunnel boring machines (TBM) to dig underground or through mountains. The method is also widely adopted in the oil and gas industries.

However; using trenchless tunneling methods with TBMs to dig subsurface tunnels for installing new water and sewer pipelines in cities, is vastly different and more challenging owing to the extensive network of subsurface pipelines already crisscrossing through the city supplying water, oil, gas, etc., disposing sewage from homes, offices, and industries and telephone and electric cables reaching every home.

As early as 1930, pipe jacking was used to install reinforced concrete pipes. The 70’s and 80’s saw a surge in rehabilitating old pipelines using trenchless technology for upgrading and increasing the capacity of existing pipelines. By the 90’s, steerable horizontal drilling machines were introduced and remain one of the best methods for installing pipelines.

With the increasing need for speedy, accurate and economical remedies to the conventional digging methods that are disruptive, and an eyesore in landscaped areas, trenchless tunneling is fast becoming a top choice for pipeline laying and rehabilitation.


When and Why Trenchless Technology is Used

In an increasingly environment-conscious society, there is a rising demand for the use of methods that cause less or no disturbance to natural habitats like palustrine wetlands, swamps, streams, lands with dense foliage and water bodies teaming with aquatic life. A number of different plant, bird, animal and fish species inhabit these places, and human activities like trenching, dewatering, channeling, etc. has taken its toll on them, even to the point of some becoming nearly extinct.

Trenchless technology has not just shown a better way to tunnel, but has proven itself to be the most feasible, eco-friendly and quick way to get the job done.

Advancements in human lifestyle and technology have increased the demand for bigger, better and cleaner spaces for living, working, recreation and educational purposes. This has put a huge demand on utilities like water supply and sewer disposal. At the same time, better infrastructure is being built to make commuting faster and easier.

More ground area is being covered with roads, cycling and walking lanes, parks, etc. Not just public spaces, even private homes have driveways and gardens under which pipelines carrying water and sewage, electric cables, telephone lines and gas pipelines, crisscross.

The problem arises when underground utilities have to be repaired, upgraded or installed. Digging up roads, public spaces, driveways and gardens has been the traditional way of carrying out these jobs, which disrupts regular vehicular and pedestrian traffic. It also takes days to complete and usually leaves the place nothing like it used to be before it was dug up. The resulting chaos is costly in terms of fuel, time and manpower required to carry out open trenching.

Trenchless tunneling has brought a great solution to all of these issues with its range of tunneling methods that require excavation only at the entry and exit points of the proposed pipeline path. It’s even better when it comes to rehabilitation because most of it can be carried out from manholes and requires little to no excavation.

Methods and Machinery Used in Trenchless Technology

Trenchless tunneling utilizes a variety of tunneling methods like microtunneling, Directional Drilling, Auger Boring, Moling, etc. Horizontal earth boring methods do not need workers to enter the workspace, but some trenchless methods like pipe ramming and utility tunneling may require entry of workers inside the borehole.

There are different types of horizontal earth boring techniques used for installing new pipelines via trenchless construction. They are:

Horizontal Directional Drilling (HDD)

During horizontal directional drilling, a pilot hole is drilled along the proposed path. The drill bit is equipped with a survey tool to monitor the progress of the borehole. The hole is then enlarged using a reamer to accommodate the required pipe size. The pipes are then pulled through the prepared hole.

Check out The Tunneling Company’s crews in action and learn about their commitment to innovation, safety and results:

Horizontal Auger Boring (HAB)

During horizontal auger boring, a horizontal shaft is driven from the drive to the reception shaft using a rotating cutting head. The excavated material is brought back to the drive shaft where it is removed. As the bore advances, a casing is pushed into place using a hydraulic jack.

Pipe Ramming

During pipe ramming, air compressor is used to hammer the steel casing inside the earth. Using air pressure, the soil is pushed out of the pipe.

Microtunneling (MTM)

Microtunneling utilizes a number of independent systems like a microtunnel boring machine (MTBM), jacking system, lubrication system, spoil removal system, guidance and remote control system, working together.

Pilot Tube Microtunneling

Pilot tube microtunneling makes use of the characteristics of HDD, HAB, and MTM along with advanced survey system like a theodolite with cameras. This method is the most accurate in line and grade.

Impact Moling

Impact moling is done by compressing the soil and pulling or pushing the pipe through the borehole that is created. It is done for short length, non-precision, small diameter pipelines. It is also known as the Compression Method.

Pipe Jacking

Pipe jacking is the method that allows workers to access the borehole while the excavation and installation of pre-fabricated pipe sections are in progress. From the drive pit, the new pipes are jacked into place as the excavation proceeds.

For carrying out rehabilitation of existing pipelines, trenchless methods like the following are used:

Differences and Characteristics of Earth Boring Techniques


S. No. Type Boring Diameter (inches) Installation height (feet) Material Application
1. HDD 2 to 48 600 to 6000 PVC, clay, FRP, steel, ductile iron, HDPE Pressure pipe, cables
2. HAB 4 to 60 600 Steel Pressure pipe, gravity pipe, road and rail crossings
3. Pipe ramming Up to 120 400 Steel Rail and road crossing
4. Pilot tube Micro-tunneling 6-10 300 Vitrified CP, Ductile iron pipe, Steel, GRP, PCP Gravity pipes
5. Compaction methods 8 or lesser 250 All types Pipes and cables


The technological advances in the field of trenchless technology for carrying out underground surveys and excavation using computerized trenching equipment, have been monumental in a relatively short span of time. As more people are becoming aware of the advantages of trenchless tunneling over open excavation, there is a surge in demand for the use of trenchless technology for pipeline installing, repairing and everything in between. Keeping the environment green by minimizing carbon footprint from machinery used in traditional excavation is becoming increasingly necessary.

Trenchless technology is the perfect solution for this, as well as for carrying out pipeline projects in delicate ecosystems that can be greatly harmed by using the open trenching methods.

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Written by Tabitha Mishra | Civil Engineer, Technical Content Writer

Tabitha Mishra

Tabitha has a Bachelors Degree in Civil Engineering from Mumbai University, India, and is currently freelancing as a technical content writer. Prior to writing, she has worked as a site engineer and site manager for various building construction, building rehabilitation, and real estate evaluation projects.

Tabitha is also certified as a Primavera project management professional and is well versed with Auto CAD. In her spare time, she does private consultation for small-sized home builders and assists with plans and permissions.

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