The Evolution of Tunnel Construction Methods in Asia: From TBM to NATM

Tunnel construction has become the most important part of Asia Pacific’s transport infrastructure development. As the region’s population density intensifies and urbanization accelerates at an unprecedented pace, underground spaces are increasingly viewed not as alternatives but as necessities.

From the bustling metropolises of Singapore and Mumbai to the mountainous terrains of the Himalayas and the high-speed rail corridors of China, tunnelling is reshaping how people and goods move across the continent.

Asia-Pacific dominates the Tunnel Construction Market with approximately 47% market share. This reflects the scale driving underground rail infrastructure in Asia, encompassing metro systems, railway tunnels, mountain crossings, and underground transport corridors that connect cities, countries, and communities.

Currently, the shift is towards two major methodologies: the Tunnel Boring Machine (TBM) and the New Austrian Tunnelling Method (NATM).

This guide explores the evolution of tunnel construction methods in Asia, comparing TBM and NATM, examining where each method performs best, and highlighting how modern infrastructure projects are increasingly combining both approaches to overcome complex geological and urban construction challenges.

Key Takeaways

• Asia Pacific leads global tunnel construction, driven by urbanization, metro rail expansion, and high-speed rail development.
• Tunnel Boring Machines (TBM) and the New Austrian Tunnelling Method (NATM) are the two primary tunnelling methods used across Asia, each suited to different geological and project requirements.
• Many of Asia’s largest infrastructure projects now combine TBM and NATM to improve construction efficiency while addressing complex ground conditions and dense urban environments.
• Advances in automation, digital monitoring, and tunnel engineering are making both methods safer, faster, and more adaptable for future transport infrastructure.

Why Tunnel Construction Is Accelerating Across Asia Pacific

Tunnel construction is accelerating across Asia Pacific as rapid urbanization, population growth, and rising transport demand reshape the region’s infrastructure priorities.

With cities becoming denser and surface land increasingly scarce, governments are investing heavily in underground transport networks that improve mobility without expanding the urban footprint.

The main factors driving this growth include:

1. Rapid Metro Rail Expansion

Countries including India, China, Singapore, Thailand, Indonesia, and Vietnam are expanding underground metro networks to ease congestion and improve public transport.

Mumbai Metro Line 3, a 33.5-kilometre fully underground corridor, deployed 17 tunnel boring machines, while Bangkok’s MRT Purple Line extension includes 3.12 kilometres of twin tunnels beneath the Chao Phraya River.

2. Growth of High-speed Rail

New high-speed rail corridors increasingly rely on tunnels to cross mountains and densely populated areas.

China’s Shenzhen-Shantou High-Speed Railway, for example, includes the 10.3-kilometre Longgang Tunnel, with bridges and tunnels accounting for more than 90% of the route.

3. Cross-border Infrastructure Development

International rail projects require advanced tunnelling to navigate diverse geological conditions.

The Mumbai-Ahmedabad High-Speed Rail corridor combines NATM and TBM construction within its 21-kilometre tunnel to maximise construction efficiency.

4. Smart City and Sustainable Transport Initiatives

Governments across the region are integrating underground transport into long-term urban development strategies, recognising tunnels as essential infrastructure for creating efficient, connected, and future-ready cities.

How Underground Infrastructure Supports APAC Transport Growth

Land constraints in Asia’s densely populated cities make underground infrastructure not merely preferable but essential. With surface space at a premium, tunnelling enables transport networks to expand without displacing communities or destroying valuable urban fabric.

Transport efficiency is dramatically improved through underground systems. Metro networks can move hundreds of thousands of passengers daily without interfering with surface traffic.

Multimodal mobility systems integrate underground rail with buses, cycling infrastructure, and pedestrian networks, creating seamless urban transport ecosystems.

Sustainable transport infrastructure benefits from tunnelling in multiple ways. Underground rail systems produce significantly lower emissions per passenger-kilometre than road transport.

Additionally, tunnels can reduce the environmental impact of mountain crossings by minimising surface disturbance and preserving natural landscapes.

Why Tunnel Engineering Is Critical for Modern Railway Infrastructure

The importance of tunnel engineering can be seen across several areas:

• Expanding urban rail networks: Underground metro systems allow cities to increase public transport capacity without acquiring expensive surface land or disrupting existing communities.
• Connecting challenging terrain: Mountain rail corridors rely on advanced tunnelling to overcome difficult geology. India’s Rishikesh-Karnaprayag railway includes the country’s longest railway tunnel (14.57 kilometres), built through the Himalayas using both TBM and NATM.
• Supporting transport hubs: Underground tunnels are increasingly used in airports and logistics facilities. Singapore’s Changi Airport Terminal 5, for example, includes passenger and baggage transfer tunnels that expand capacity while maintaining efficient surface operations.
• Building more resilient infrastructure: Underground rail systems are better protected from extreme weather, surface congestion, and other external disruptions, making them a key component of reliable, long-term transport infrastructure as cities adapt to climate and population pressures.

Understanding the Main Tunnel Construction Methods Used in Asia

Several tunnel excavation methods are employed across Asia Pacific, each suited to specific ground conditions, project scales, and urban contexts.

What Is Tunnel Boring Machine (TBM) Construction?

Tunnel Boring Machine construction represents the pinnacle of mechanized tunnelling technology. TBMs are massive cylindrical machines, typically 80 to 100 metres long, that excavate soil and rock while simultaneously installing tunnel lining segments.

The TBM process is highly automated. A rotating steel cutterhead at the front of the shield breaks through ground conditions ranging from soft soil to hard rock. Excavated material is removed through the machine, while precast concrete segments are erected behind the cutterhead to form the tunnel’s permanent lining.

Advantages of TBM Tunnel Construction in Urban Rail Projects

Key advantages of TBM tunnelling include:

• High precision: TBMs produce consistent tunnel dimensions and alignment, meeting the strict accuracy required for modern railway infrastructure.
• Minimal surface disruption: Because excavation takes place underground, TBMs reduce the impact on roads, businesses, utilities, and daily urban activities compared with cut-and-cover construction.
• Faster construction: TBMs can operate continuously, often advancing several metres each day, making them highly efficient for long railway and metro tunnels.
• Improved worker safety: The machine’s protective shield provides immediate ground support during excavation, reducing workers’ exposure to unstable ground conditions.
• Greater efficiency for large urban projects: Singapore’s Cross Island Line Phase 2 demonstrates this advantage with the country’s longest single TBM drive (5 kilometres), using a Semi-Continuous Advance system that allows tunnel lining installation and excavation to take place simultaneously, improving productivity.

Challenges of TBM Tunnel Construction in Asia Pacific

While TBMs offer significant advantages, they also present technical and financial challenges, particularly in Asia Pacific’s diverse geological and environmental conditions.

Some of the key challenges include:

• High capital costs: TBMs are expensive to design, manufacture, transport, and operate. For shorter tunnels or less complex projects, their cost can outweigh the benefits compared with methods such as NATM.
• Complex geological conditions: Mixed ground, fault zones, high in-situ stress, water-bearing formations, and the challenging geology of regions such as the Himalayas can reduce TBM performance and increase construction risks.
• Project-specific machine design: TBMs are typically customized for each project’s ground conditions, adding to procurement time, engineering complexity, and overall project costs.
• Maintenance requirements: Excavating through abrasive rock or difficult ground accelerates wear on cutters and other components, leading to frequent maintenance and potential downtime.
• Groundwater and flooding risks: High groundwater pressure and water ingress, particularly in monsoon-prone regions, can interrupt tunnelling operations, complicate excavation, and require extensive water management measures.

What Is the New Austrian Tunnelling Method (NATM)?

The New Austrian Tunnelling Method (NATM) is a tunnelling approach that uses the surrounding ground as part of the tunnel’s support system.

Instead of relying on a rigid structure from the outset, NATM strengthens and stabilizes the excavated ground through staged excavation, continuous monitoring, and flexible support measures that can be adjusted as conditions change.

The method is based on several core principles:

• Sequential excavation: The tunnel is excavated in stages, with ground support installed immediately after each excavation cycle.
• Flexible ground support: Depending on site conditions, support systems typically include shotcrete (sprayed concrete), rock bolts, steel ribs, and other reinforcement measures.
• Ground stabilization: NATM mobilizes the natural strength of the surrounding rock or soil, allowing it to become an integral part of the tunnel’s load-bearing system.
• Continuous monitoring: Engineers use geotechnical instruments to monitor ground movement and stress in real time, enabling support systems to be adjusted as excavation progresses.

Moreover, NATM is widely used for mountain tunnels, variable rock formations, station caverns, cross passages, and other rail infrastructure where changing ground conditions make TBM construction less practical or economical.

Why NATM Is Commonly Used in Complex Geological Conditions

NATM is widely used in Asia’s mountain regions because it can adapt to changing ground conditions throughout the excavation process. Unlike TBMs, which perform best in relatively consistent geology, NATM allows engineers to modify excavation and support measures as rock quality, fault zones, or groundwater conditions change.

Its flexibility, lower equipment requirements, and ability to handle unpredictable terrain make it the preferred choice for many tunnel projects in the Himalayas, Southeast Asia, and western China, where geological conditions can vary significantly over short distances.

Advantages and Limitations of NATM Tunnel Construction

NATM offers several benefits, particularly for projects with complex geology, but it also comes with trade-offs that must be considered during project planning.

Key advantages include:

• Highly adaptable: NATM can accommodate changing rock conditions, mixed geology, and complex tunnel geometries.
• Flexible support design: Engineers can modify support systems during construction based on real-time ground behavior.
• Lower equipment costs: The method requires less specialized machinery than TBMs, reducing mobilization and equipment expenses.
• Suitable for complex tunnel layouts: NATM works well for station caverns, cross passages, transition tunnels, and irregular tunnel profiles.
• Cost-effective for shorter or variable-ground projects: It is often the more economical option where deploying a TBM is impractical.

Limitations of NATM are:

• Slower construction: Sequential excavation and support installation generally make NATM slower than TBM tunnelling.
• Requires experienced engineers: Successful implementation depends on continuous monitoring and skilled decision-making throughout construction.
• Higher worker exposure: Construction crews work closer to freshly excavated ground, increasing safety risks compared with enclosed TBM operations.
• Potential for delays: Unexpected ground instability, water ingress, or weak rock conditions can slow excavation and require additional support measures.

TBM vs NATM: Which Tunnel Construction Method Works Best in Asia?

The choice between TBM vs NATM depends on project-specific factors including geology, length, urban context, and budget.

Why APAC Geology Often Requires Hybrid Tunnel Construction Approaches

Asia Pacific’s diverse geology means that a single tunnelling method is rarely suitable for an entire project.

Common reasons for adopting hybrid construction include:

• Changing ground conditions: Projects often pass through soft soils, hard rock, fault zones, and water-bearing formations within the same tunnel alignment.
• Mountainous terrain: Regions such as the Himalayas, western China, and Southeast Asia experience highly variable geology that requires flexible construction methods.
• Complex urban construction: TBMs are typically used for long-running tunnels, while NATM is preferred for station caverns, cross passages, and transition sections.
• Seismic and environmental challenges: Earthquake-prone regions and monsoon climates require tunnelling methods that can adapt to ground movement and groundwater conditions.
• Proven success in major projects: The Rishikesh-Karnaprayag railway, China’s Longgang Tunnel, and Mumbai Metro Line 3 all combine TBM and NATM to optimize construction across varying geological conditions.

How Climate and Urban Density Affect Tunnel Engineering in Asia

Climate and urbanization significantly influence tunnel design and construction across Asia Pacific.

Key challenges include:

• Tropical climate and groundwater management: Heavy rainfall and high water tables increase the risk of water ingress, requiring advanced drainage and pressure control systems.
• Construction beneath rivers and aquifers: Projects such as Bangkok’s MRT Purple Line require precise TBM operations to safely tunnel through water-bearing ground.
• Growing underground congestion: Mature cities like Singapore and Tokyo must integrate new tunnels with existing metro lines, utilities, and pedestrian networks.
• Climate resilience: Modern tunnels are designed to withstand flooding, extreme weather, and other climate-related risks while providing reliable long-term transport infrastructure.

Engineers must account for heavy rainfall, high groundwater levels, and increasingly congested underground spaces while ensuring long-term infrastructure resilience.

Major Tunnel Construction Projects Shaping Asia Pacific

Major infrastructure projects across Asia Pacific demonstrate how TBM, NATM, and hybrid tunnelling methods are being applied to meet different geological and urban challenges.

• Singapore MRT expansions

The Cross Island Line Phase 2 includes a 5-kilometre single TBM drive, the longest in Singapore, using a Semi-Continuous Advance system to improve construction efficiency.

The Downtown Line Stage 2 combined TBM, NATM, and cut-and-cover methods to construct tunnels and underground stations beneath dense urban areas.

• Mumbai Metro Line 3 (India)

This 33.5-kilometre fully underground metro corridor deployed 17 Tunnel Boring Machines, making it one of India’s largest TBM operations. NATM was also used for station access tunnels and short tunnel sections where TBMs were less practical.

• Bangkok MRT Purple Line (Thailand)

The southern extension includes 3.12 kilometres of twin tunnels beneath the Chao Phraya River, excavated using Earth Pressure Balance (EPB) TBMs with an internal tunnel diameter of approximately 5.7 metres.

• Shenzhen-Shantou High-Speed Railway (China)

The Longgang Tunnel, measuring 10,307 metres, is designed for trains operating at 350 km/h. The project combines TBM and NATM to address varying geological conditions along the alignment.

• Rishikesh-Karnaprayag Railway (India)

The project includes India’s longest railway tunnel (14.57 kilometres). Approximately 10.4 kilometres are being excavated using a 9.11-metre-diameter TBM, while the remaining 4.11 kilometres are constructed using NATM, illustrating a hybrid tunnelling approach.

Underground Metro Expansion Projects Across Asia

Metro tunnel construction is accelerating across the region. India’s metro networks in Mumbai, Delhi, and other cities are expanding rapidly.

At the same time, Singapore continues to extend its world-class MRT system. Bangkok, Jakarta, and Ho Chi Minh City are developing or expanding underground metro lines to address severe urban congestion.

High-Speed Rail and Mountain Tunnel Projects in APAC

High-speed rail tunnel construction represents the cutting edge of the industry.

China’s Shenzhen-Shantou High-Speed Railway, with its 92.6% bridge-tunnel ratio, demonstrates how tunnelling enables high-speed rail through challenging terrain. Likewise, the Mumbai-Ahmedabad bullet train corridor’s 21-kilometre tunnel showcases India’s ambitions.

How Tunnel Construction Technology Is Evolving

Tunnel construction technology is advancing rapidly across multiple fronts:

• AI-assisted excavation: Artificial intelligence is being used to optimize TBM operating parameters, improving excavation efficiency while reducing ground settlement. Bangkok’s MRT Blue Line has demonstrated the use of AI for shield tunnelling optimization in soft ground.
• Digital twins: Virtual models are helping engineers simulate tunnel construction, monitor infrastructure performance, and support predictive maintenance. Bangkok has implemented a physics-based digital twin for tunnel rehabilitation, while China is expanding digital twin platforms for tunnel management.
• Smart monitoring systems: Sensors continuously track ground movement, groundwater conditions, and structural performance, allowing engineers to identify potential issues early and make informed construction decisions.
• Rail Automation and remote operations: Automated control systems and remote TBM operation are improving worker safety, reducing manual intervention, and increasing construction productivity.
• Sustainable construction practices: Contractors are adopting low-carbon construction methods, including recycling steel and concrete. Research shows that increasing recycling rates to 10-30% can reduce greenhouse gas emissions from tunnel construction by approximately 5.5-9.9%.

Smart Tunnel Infrastructure and Digital Engineering Systems

Smart tunnel infrastructure represents the future of tunnel engineering. Digital engineering systems integrate design, construction, and operation data into unified platforms that enable better decision-making throughout the project lifecycle.

These systems support intelligent supervision, predictive control, and data fusion that enhance tunnel performance, safety, and operational intelligence.

Sustainable Tunnel Construction and Environmental Considerations

Environmental considerations are increasingly central to tunnel construction. Underground transport systems reduce surface disruption and preserve natural landscapes.

However, tunnelling itself has environmental impacts, constructing one kilometre of subway shield tunnel can generate approximately 19,294 tonnes of CO₂ equivalent.

The industry is responding with green construction practices, material recycling, and energy-efficient equipment. The Shenzhen-Zhongshan Bridge and Tunnel project in China exemplifies efforts to quantify and reduce carbon emissions from large-scale infrastructure.

What Tunnel Construction Growth Means for Infrastructure and Railway Companies

The expansion of tunnel construction across Asia Pacific creates significant opportunities for:

• EPC firms (Engineering, Procurement, Construction) are securing major contracts across the region. Larsen & Toubro’s work on the Rishikesh-Karnaprayag project and Mumbai Metro demonstrates the scale of opportunity.
• Tunnel engineering companies are in high demand as projects multiply. Specialised expertise in TBM operation, NATM design, and hybrid methods is increasingly valuable.
• TBM manufacturers such as Herrenknecht, Terratec, and CRCHI are expanding their presence in Asia. CRCHI’s “Longgang No.2” TBM represents the latest generation of super-large diameter machines.
• Rail infrastructure suppliers benefit from the associated demand for track, signalling, ventilation, and other systems.
• Smart mobility companies are finding opportunities in digital twins, AI-assisted operations, and intelligent transport systems.
• APAC rail investment continues to grow, driven by urbanisation, population growth, and smart city development. Underground transport demand shows no signs of slowing.

Growing Demand for Tunnel Engineering Expertise in Asia Pacific

The scale of the project pipeline creates unprecedented demand for tunnel engineering expertise. Engineers with experience in TBM operations, NATM design, ground improvement, and hybrid methods are increasingly sought after.

Opportunities for Railway Infrastructure and Construction Companies

Railway infrastructure in Asia is expanding rapidly, creating opportunities across the supply chain. From consulting engineering to construction, from equipment manufacturing to operations and maintenance, the tunnel construction boom supports a broad ecosystem of companies and professionals.

How InnoTrans Asia Supports Tunnel Construction and Railway Infrastructure Innovation

InnoTrans Asia, taking place in Singapore from 7–9 September 2027, brings together the region’s rail and tunnel construction industry to showcase the latest technologies, exchange expertise, and support the future of railway infrastructure across Asia Pacific.

The event provides opportunities to:

• Connect railway authorities, infrastructure developers, and tunnel engineering companies.
• Discover innovations in railway technology, railway infrastructure, public transport, railway interiors, and tunnel construction.
• Share best practices for metro, high-speed rail, and underground infrastructure projects.
• Build partnerships that support future rail and tunnelling developments across the region.

As the regional edition of the globally recognized InnoTrans exhibition, the event strengthens collaboration between industry stakeholders and accelerates the adoption of innovative railway and tunnel construction solutions.