In today’s age of infrastructure growth and rapid urbanisation, building tunnels for metro systems, highways, water supply, and sewage projects has become essential. Among the various methods of tunnel construction, the Tunnel Boring Machine (TBM) stands out as the most advanced and efficient method, especially for large-scale urban tunnelling projects in India.

This blog explains everything you need to know about TBMs—from their working to advantages and applications in Indian conditions.

What is a Tunnel Boring Machine (TBM)?

A Tunnel Boring Machine (TBM) is a heavy mechanical equipment used to excavate tunnels with a circular cross-section through various ground conditions, such as soil, rock, or mixed strata. Also known as a “mole”, a TBM can bore through the ground while simultaneously supporting the tunnel wall, thus making the tunnelling process safer and more efficient.

Components of a TBM

A TBM is a complex system made up of various parts that perform different functions during tunnelling:

• Cutterhead: The rotating front part that breaks the soil or rock.
• Thrust System: Pushes the TBM forward.
• Conveyor System: Transports the excavated material out of the tunnel.
• Shield: Protects the tunnel and workers.
• Grouting System: Fills the gap between the tunnel lining and soil.
• Lining Erector: Installs concrete segments to form the tunnel wall.

Types of Tunnel Boring Machines

TBMs are selected based on the geology of the tunnelling site. The common types include:

1. Earth Pressure Balance (EPB) TBM: Used in soft soils like clay, silt, or sand.
2. Slurry Shield TBM: Used in loose, water-bearing soils.
3. Hard Rock TBM: Ideal for tunnelling through solid rock formations.
4. Double Shield TBM: Suitable for mixed ground conditions.

In India, EPB and Slurry Shield TBMs are widely used in metro rail projects like Delhi Metro, Mumbai Metro, and Bangalore Metro.

How Does a TBM Work?

Here’s a simplified process of how a TBM functions:

1. The cutterhead at the front rotates and grinds the ground ahead.
2. Excavated material is collected and moved using a conveyor or muck car.
3. As the machine moves forward, precast concrete segments are placed behind it to line the tunnel.
4. The grouting system fills gaps between the soil and lining, preventing settlement.
5. The process continues until the tunnel is completed.

Advantages of Using TBM in Construction

• ✅ Speed: Faster than traditional drilling and blasting.
• ✅ Safety: Provides a safe working environment for workers.
• ✅ Minimal Surface Disruption: TBMs reduce disturbance to roads and buildings above.
• ✅ Precision: Tunnels are formed in precise shapes and alignments.
• ✅ Cost-effective for long tunnels: Though initial cost is high, it becomes economical for longer lengths.

Applications of TBM in India

TBMs have revolutionised tunnelling in India. Some prominent Indian projects where TBM has played a key role:

• Delhi Metro: One of the earliest adopters of TBM technology in India.
• Mumbai Metro Line 3: Used multiple Earth Pressure Balance TBMs for underground sections.
• Bangalore Metro (Namma Metro): Faced tough geological conditions but successfully used Slurry TBMs.
• Chennai Metro: Made extensive use of TBMs for coastal underground tunnelling.
• Mumbai Coastal Road Project: TBM named ‘Mavala’ was deployed for tunnelling under marine conditions.

How Much Does a Tunnel Boring Machine Cost?

The cost of a TBM varies depending on its size, type, and purpose. On average:

• A standard TBM can cost between ₹150 crore to ₹500 crore.
• Large-diameter machines, like those used for highway or river tunnels, may exceed ₹600 crore.
• Additionally, there are high operating and maintenance costs, including crew, power supply, lubrication, and spares.

Does India Have Tunnel Boring Machines?

Yes, India has adopted TBM technology on a large scale. While most TBMs used in India are imported from global manufacturers like Herrenknecht (Germany), Robbins (USA), and CRCHI (China), Indian companies now have growing capabilities in TBM operation, assembly, and maintenance.

For example, BEML (Bharat Earth Movers Limited), a public sector company, has started working towards domestic TBM development. Also, many TBMs are refurbished and reused by Indian construction firms such as Afcons, L&T, and ITD Cementation.

Examples of TBMs Used in India

1. Mavala – A massive Slurry TBM used in the Mumbai Coastal Road Project, with a diameter of over 12 metres.
2. Krishna 1 & 2 – EPB TBMs used for the Hyderabad Metro Rail.
3. Urja & Vindhya – TBMs used in Mumbai Metro Line 3, named after Indian rivers.
4. Godavari – Used in Chennai Metro, tailored for tunnelling through water-logged coastal soil.
5. Ava & Lavi – TBMs deployed for Bangalore Metro, designed to handle both granite and loose soil.

These machines are often named to honour local heritage, gods, rivers, or women engineers to reflect community pride and ownership.

Challenges in TBM Usage in India

Despite its advantages, using TBMs in India comes with some challenges:

• Complex geology: Varies from hard rock to soft soil within a short distance.
• High initial cost: TBMs are expensive to procure and operate.
• Logistics and space: Requires large launch and retrieval shafts.
• Water table issues: In coastal cities like Mumbai and Chennai, water seepage is a concern.

Indian Standards & Guidelines

In India, there are no exclusive IS codes for TBM operations yet, but some standards and guidelines are followed:

• IS 4756:1978 – Safety code for tunnelling work.
• MoHUA Guidelines – Used in metro and urban tunnelling.
• International Standards – Like BS EN and ASTM, are also referred for TBM machinery and lining systems.

Future of TBM in Indian Infrastructure

As India continues to invest in urban infrastructure, metros, high-speed rail, and water supply tunnels, the use of TBM will only grow. With advances in manufacturing and support systems, TBMs will become more affordable and adaptable to India’s challenging ground conditions.

Conclusion🎯

The Tunnel Boring Machine (TBM) has become a vital part of India’s construction landscape. Whether it’s expanding metros or improving coastal roads, TBMs ensure speed, safety, and quality in underground construction. While there are challenges, technological advancements and experience will continue to make TBM tunnelling more efficient and widespread across India.

Frequently Asked Questions (FAQs)

1. What does TBM stand for in construction?

TBM stands for Tunnel Boring Machine. It is a specialised machine used to excavate tunnels in various soil and rock conditions with high precision and safety.

2. How does a TBM work?

A TBM uses a rotating cutterhead to break and remove soil or rock. The debris is transported out of the tunnel using a conveyor system. Simultaneously, pre-cast concrete segments are installed to support the tunnel walls.

3. Is TBM used in India?

Yes, TBMs are widely used in India for major infrastructure projects like metro rail systems, highways, and sewer tunnels. Cities like Mumbai, Delhi, Bangalore, and Chennai use TBMs for urban tunnelling.

4. How much does a TBM cost in India?

A Tunnel Boring Machine in India can cost between ₹150 crore to ₹600 crore, depending on its type, size, and features. Operational and maintenance costs are also significant.

5. What are the types of TBMs?

The common types of Tunnel Boring Machines include:

• Earth Pressure Balance (EPB) TBM
  
• Slurry TBM
  
• Hard Rock TBM
  
• Double Shield TBM
  

Each type is chosen based on the ground conditions.

6. What are some examples of TBM machines used in India?

Notable TBMs in India include:

• Mavala (Mumbai Coastal Road)
• Urja and Vindhya (Mumbai Metro Line 3)
• Krishna (Hyderabad Metro)
• Ava and Lavi (Bangalore Metro)

7. Who manufactures TBMs?

TBMs are mainly manufactured by international companies such as Herrenknecht (Germany), Robbins (USA), and CRCHI (China). Indian companies like BEML are exploring indigenous TBM development.

8. Why is TBM preferred over traditional tunnelling?

TBMs offer faster excavation, higher safety, minimal disturbance to surface activities, and better finish quality. This makes them ideal for tunnelling in busy urban areas.