Microtunneling Explained: Trenchless Construction Guide

What is Microtunneling?

Microtunneling is a construction method that uses a small, remote-controlled Microtunnel Boring Machine (MTBM) to install pipes underground without digging long trenches. It employs a slurry system for soil removal and face support, laser guidance, and hydraulic jacking to achieve precise alignment in challenging conditions with minimal surface disruption.

What are the Advantages and Disadvantages of Microtunneling?

Pioneered by the Japanese company Iseki & Co., microtunneling addresses one of the most challenging constraints in underground construction: the inability to cause surface disruption in urban environments. Due to its increased precision and effectiveness, numerous companies utilize this technique worldwide; however, it also presents its share of challenges.

Equipment and Systems Used

Digging tunnels is complex, risky, and labor-intensive. Microtunneling projects have become much easier with the right technologies and engineered tools. Understanding what each does is foundational to excavation safety.

MTBM

The MTBM is the remote-controlled drilling machine that cuts through the ground. It manages the pressure at the tunnel face, handles the flow of the soil slurry, and keeps the tunnel stable while pushing the pipe forward with high accuracy.

Pipe jacking system

This powerful hydraulic system steadily pushes the pipeline behind the MTBM. It applies the necessary force to move the tunnel forward, maintain the correct position, and support the pipe segments as they are installed.

Bentonite slurry system

A closed-loop pumping system circulates a specialized fluid (bentonite slurry) to the front of the MTBM. Its job is to support the soil face, carry the excavated material out, and control the pressure to prevent the ground from collapsing.

Guidance and control systems

Laser targets, sensors, and computers constantly track and adjust the MTBM's position. It ensures the pipeline stays on the exact line and depth, allowing for precise tunneling even on deep or curved paths.

Launch and reception shafts

These are the vertical entry and exit points dug into the ground. They’re used to lower the MTBM and pipes into position, house the powerful jacking equipment, and allow workers to connect the new pipeline once the tunneling is complete.

What Types of Projects is Microtunneling Best Suited For?

Trenchless construction is an excellent solution for challenging underground work, but it isn't always the ideal method. Here are the specific instances where microtunneling techniques are best utilized:

• Urban utility installations: Installing water, sewer, gas, and telecom lines under busy city streets requires minimal surface disruption and traffic closures.

• River and water crossings: Laying pipelines beneath rivers, lakes, and drainage channels becomes easier despite high groundwater pressures. The technique also doesn’t disturb aquatic systems.

• Road and rail crossings: Utilities can pass beneath highways and railways without stopping traffic or affecting structural integrity.

• Contaminated or sensitive sites: The method is suited for unstable soils with hazardous materials, heritage zones, and protected ecosystems. Aside from reducing environmental impacts, this enhances worker safety.

How Does Microtunneling Work?

Microtunneling follows a strict, systematic process where each stage is essential for accuracy and safety. Consistently follow these steps to reduce risks, prevent ground issues, and ensure a smooth, controlled underground installation:

1. Prepare the site and conduct a geotechnical survey.

The project begins with soil investigations, utility mapping, shaft excavation, and site setup. A pre-start excavation checklist usually includes the following:

• Permit verification

• Soil stability investigation

• Equipment readiness checks

• Dewatering plans

• Personal Protective Equipment (PPE) needs

• Hazard controls

2. Assemble the MTBM and launch it from the shaft.

The MTBM, jacking frame, slurry pipes, and guidance systems are installed in the launch shaft. Crews connect power, hydraulics, and instrumentation before initiating the first push.

3. Excavate the tunnel and jack the pipes forward.

The cutterhead digs through the ground while hydraulic jacks push pipe segments behind it. This is done sequentially, the pipes forming the tunnel as the MTBM advances underground.

4. Manage slurry pressure and remove excavated spoil.

Bentonite slurry supports the tunnel face and transports material back to the separation plant. Spoil is screened, and clean slurry is recirculated to maintain safe pressure levels.

5. Monitor alignment and make real-time adjustments.

Laser guidance and sensors track the line and grade continuously. Operators adjust steering as needed. Having an excavation and trenching checklist can help workers track the process and flag issues by doing these:

• Monitoring ground movement

• Observing equipment pressures and alarms

• Keeping a watch on shaft stability

6. Receive and retrieve the MTBM at the exit shaft.

Once the breakthrough occurs, the MTBM enters the reception shaft. Crews disconnect utilities, lift the machine out, and remove slurry lines and guidance components.

7. Commission the pipeline and complete backfilling.

The deployed pipeline is tested for integrity, cleaned, and connected to the system. Shafts are then backfilled, compacted, and restored to original or required surface conditions.

A leading Australian mining and construction group, Byblos Constructions utilizes robust digital solutions to streamline safety, quality, and compliance across its remote projects. The resulting real-time communication and collaboration minimizes team "blind spots" and enables faster action—a critical advantage for complex projects like microtunneling.